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A molecular dynamics deposition model has been used to simulate the growth of rare gas matrices doped with atoms of the group 12 elements zinc, cadmium and mercury. This study investigates the sites occupied by Zn, Cd and Hg metal atoms when isolated in the solid rare gases. To probe the results, the resonance 1 P 1 ← 1 S 0 transitions of the matrix-isolated metal atoms were calculated and compared with the recorded spectra of the M/RG solids. The theoretical spectroscopy obtained in this work was generated using the molecular dynamics with quantum transitions method. In Ne matrices the metal atoms preferably occupy tetra- and hexa-vacancy sites while in the case of Xe matrices, only the single vacancy site is formed. For Ar and Kr matrices Zn but especially Cd can be trapped in tetra- and hexa-vacancy sites in addition to single-vacancy sites, while Hg atoms show exclusive occupancy in single vacancy sites.A molecular dynamics deposition model has been used to simulate the growth of rare gas matrices doped with atoms of the group 12 elements zinc, cadmium and mercury. This study investigates the sites occupied by Zn, Cd and Hg metal atoms when isolated in the solid rare gases. To probe the results, the resonance 1 P 1 ← 1 S 0 transitions of the matrix-isolated metal atoms were calculated and compared with the recorded spectra of the M/RG solids. The theoretical spectroscopy obtained in this work was generated using the molecular dynamics with quantum transitions method. In Ne matrices the metal atoms preferably occupy tetra- and hexa-vacancy sites while in the case of Xe matrices, only the single vacancy site is formed. For Ar and Kr matrices Zn but especially Cd can be trapped in tetra- and hexa-vacancy sites in addition to single-vacancy sites, while Hg atoms show exclusive occupancy in single vacancy sites.

Molecular dynamics calculations, based on the diatomics-in-molecules method, have been used to probe the manifestations of spin-orbit (SO) coupling in the experimental absorption bands of atomic sodium isolated in solid xenon. Inclusion of SO coupling of –320 cm−1 in spectral simulations of the 3 p 2 P ← 3 s 2 S transition leads to unequal band spacings which very closely match the asymmetrical bandshape observed for blue single vacancy (SV) site occupancy. This SO value, extracted in a previous MCD study, reveals the dramatic change in the effective SO coupling constant of the Na atom (from the gas phase value of +17 cm−1) in solid Xe when it is close to the 12 xenon atoms in the first surrounding sphere. In contrast, the symmetrical three-fold split band of the red tetra vacancy (TV) site in Na/Xe is not affected nearly as much by SO coupling. This reflects a greatly reduced “external heavy atom” effect when the 24 Xe atoms surrounding the Na atom in TV are located at greater distances. The contrasting behavior of sodium in the SV and TV sites suggests a strong dependence of the SO coupling strength on the Na–Xe distance.Molecular dynamics calculations, based on the diatomics-in-molecules method, have been used to probe the manifestations of spin-orbit (SO) coupling in the experimental absorption bands of atomic sodium isolated in solid xenon. Inclusion of SO coupling of –320 cm−1 in spectral simulations of the 3 p 2 P ← 3 s 2 S transition leads to unequal band spacings which very closely match the asymmetrical bandshape observed for blue single vacancy (SV) site occupancy. This SO value, extracted in a previous MCD study, reveals the dramatic change in the effective SO coupling constant of the Na atom (from the gas phase value of +17 cm−1) in solid Xe when it is close to the 12 xenon atoms in the first surrounding sphere. In contrast, the symmetrical three-fold split band of the red tetra vacancy (TV) site in Na/Xe is not affected nearly as much by SO coupling. This reflects a greatly reduced “external heavy atom” effect when the 24 Xe atoms surrounding the Na atom in TV are located at greater distances. The contra...

International audience; A detailed characterisation of the luminescence recorded for the 6p 1P1–6s 1S0 transition of atomic barium isolated in annealed solid xenon has been undertaken using two-dimensional excitation–emission (2D-EE) spectroscopy. In the excitation spectra extracted from the 2D-EE scans, two dominant thermally stable sites were identified, consisting of a classic, three-fold split Jahn-Teller band, labeled the blue site, and an unusual asymmetric 2 + 1 split band, the violet site. A much weaker band has also been identified, whose emission is strongly overlapped by the violet site. The temperature dependence of the luminescence for these sites was monitored revealing that the blue site has a non-radiative channel competing effectively with the fluorescence even at 9.8 K. By contrast, the fluorescence decay time of the violet site was recorded to be 4.3 ns and independent of temperature up to 24 K. The nature of the dominant thermally stable trapping sites was investigated theoretically with Diatomics-in-Molecule (DIM) molecular dynamics simulations. The DIM model was parameterized with ab initio multi-reference configuration interaction calculations for the lowest energy excited states of the Ba⋅Xe pair. The simulated absorption spectra are compared with the experimental results obtained from site-resolved excitation spectroscopy. The simulations allow us to assign the experimental blue feature spectrum to a tetra-vacancy trapping site in the bulk xenon fcc crystal—a site often observed when trapping other metal atoms in rare gas matrices. By contrast, the violet site is assigned to a specific 5-atom vacancy trapping site located at a grain boundary.

A detailed characterization is made of the distinct sites occupied by atomic barium isolated in the three rare gas hosts Ar, Kr, and Xe in excitation scans extracted from the recorded total 6s6p 1 P1 → (6s)2 1S0 fluorescence. Extensive use has been made of twodimensional excitation/emission (2D-EE) spectroscopy to achieve a comprehensive characterization for the wide variety of sites present in the Ba/RG matrix systems. The 2D-EE technique has proved to be a very powerful method to probe the effects of strong intersite reabsorption when extensive spectral overlap occurs between emission and resonance 6s6p 1 P1 ← (6s)2 1S0 absorption of barium atoms occupying multiple sites. Two-dimensional excitation/emission scans have also been used in this study to monitor the effects of sample annealing and thereby identify the thermally stable sites of isolation. Sites of the same type occupied by atomic barium in the three host solids are identified in resolved excitation spectra and are associated on the basis of the observed matrix shift versus host polarizability. Following site associations, the photophysical properties of each matrix site were characterized revealing that the Stokes shift was greatest in the blue site, smallest for the violet site, and intermediate for the green site. The emission temperature dependences and excited state lifetimes were recorded, indicating that measured radiative lifetimes of 4−5 ns were in good agreement with the gas phase value of 8.4 ns when corrected for the effective field of the solids. The only exception to this was the blue site in Ba/Xe, where a nonradiative quenching channel exists even at 9.8 K that competes effectively with the nanosecond fluorescence. An unusual, asymmetric 2 + 1 excitation band has been recorded for atomic barium in the three rare gas hosts in addition to the threefold split, Jahn−Teller bands typically observed for P ← S absorptions of matrix-isolated metal atoms. Possible assignments of the sites responsible for these band shapes are made on the basis of recent spectral simulations obtained from molecular dynamics calculations on the Ba/Xe system.

Mutations in the human DJ-1/PARK7 gene are associated with familial Parkinson’s disease. DJ-1 belongs to a large, functionally diverse family with homologues in all biological kingdoms. Several activities have been demonstrated for DJ-1: an antioxidant protein, a redox-regulated molecular chaperone and a modulator of multiple cellular signalling pathways. The majority of functional studies have focussed on human DJ-1 (hDJ-1), but studies on DJ-1 homologues in Drosophila melanogaster, Caenorhabditis elegans, Dugesia japonica and Escherichia coli also provide evidence of a role for DJ-1 as an antioxidant. Here, we show that dehydration is a potent inducer of a dj-1 gene in the anhydrobiotic nematode Panagrolaimus superbus. Our secondary structure and homology modelling analyses shows that recombinant DJ-1 protein from P. superbus (PsuDJ-1.1) is a well-folded protein, which is similar in structure to the hDJ-1. PsuDJ-1.1 is a heat stable protein; with T1/2 unfolding transition values of 76 and 70 °C obtained from both circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) measurements respectively. We found that PsuDJ-1.1 is an efficient antioxidant that also functions as a ‘holdase’ molecular chaperone that can maintain its chaperone function in a reducing environment. In addition to its chaperone activity, PsuDJ-1.1 may also be an important non-enzymatic antioxidant, capable of providing protection to P. superbus from oxidative damage when the nematodes are in a desiccated, anhydrobiotic state.

Isolation of the heavier alkaline earth metals Ba and Sr in the solid rare gases (RGs) Ar, Kr, and Xe is analysed with absorption spectroscopy and interpreted partly with the assistance of ab initio calculations of the diatomic M ⋅ RG ground state interaction potentials. The y(1)P ← a(1)S resonance transitions in the visible spectral region are used to compare the isolation conditions of these two metal atom systems and calcium. Complex absorption bands were recorded in all three metal atom systems even after extensive sample annealing. Coupled cluster calculations conducted on the ground states of the nine M ⋅ RG diatomics (M = Ca, Sr, and Ba; RG = Ar, Kr, and Xe) at the coupled cluster single, double, and non-iterative triple level of theory revealed long bond lengths (5 Å) and shallow bound regions (130 cm(-1)). All of the M ⋅ RG diatomics have bond lengths considerably longer than those of the rare gas dimers, with the consequence that isolation of these metal atoms in a single substitutional site of the solid rare gas is unlikely, with the possible exception of Ca/Xe. The luminescence of metal dimer bands has been recorded for Ba and Sr revealing very different behaviours. Resonance fluorescence with a lifetime of 15 ns is observed for the lowest energy transition of Sr2 while this transition is quenched in Ba2. This behaviour is consistent with the absence of vibrational structure on the dimer absorption band in Ba2 indicating lifetime broadening arising from efficient relaxation to low-lying molecular states. More extensive 2D excitation-emission data recorded for the complex site structures present on the absorption bands of the atomic Ba and Sr systems will be presented in future publications.

Thin cryogenic samples of inert gas solids doped with free-base tetraazaporphine (H2TAP) were irradiated with a tunable pulsed laser. Under resonant electronic excitation of the guest, specific vibronic transitions of the fluorescence spectra were found to be strongly enhanced with only a moderate increase of the laser power. This enhancement is due to stimulated emission (SE). The characteristics of SE bands are described in the three hosts (Ar, N2, and Ne) explored, as well as their excitation spectra. SE is observed in transitions involving different vibrational modes of the guest, depending on the host and the electronic excitation. The results are discussed in comparison with previous works on other tetrapyrrolic molecules trapped in inert gas matrices. From this comparison the key features required to observe SE are deduced to be: (1) SE can be obtained with various tetrapyrrolic molecules; (2) free-base molecules are preferable to their metallo-counterparts; (3) the results highlight a specific molecular vibrational mode involved in the process; and (4) cryogenic crystal structures are also of importance in the detection of SE.

Pair-potentials calculations of the 3P1↔1S0 absorption and emission energies of atomic mercury isolated in solid Ar, Kr, and Xe are conducted and compared with the spectral bands recorded in Hg/RG matrices. The Hg⋅RG pair potentials used are derived from spectroscopic studies of the mercury atom–rare gas atom diatomics and are implemented in a localized Hg⋅RG18 cluster model to simulate the spectroscopy of Hg atoms isolated in substitutional sites of the solid rare gases. The calculated absorptions are all on the red wing of the observed matrix bands and from these favorable comparisons, substitutional site occupancy is identified for ground state atomic mercury. A pairwise sum of the Hg(3P1)⋅RG [A 30+(3Π)] and [B 31] state potentials is used to examine the vibronic modes of the excited 3P1 state Hg⋅RG18 clusters which lead to stabilization. The energetics of waist and body vibronic modes, involving motion of the lattice atoms with respect to the excited state mercury atom and motion of this atom in the solid, respectively, were calculated for the three symmetry poles of the cubo-octahedral substitutional sites. Excited state stabilization was found for the waist mode of all the Hg/RG systems in the three possible coordinate systems, i.e., based on the fourfold, threefold, and twofold symmetry systems. In contrast, the body modes were stabilized only in Hg/Xe. The difference between Hg/Xe and the other Hg/RG systems is related to the larger substitutional site size presented by the former system. The three components identified in the recorded emission bands are correlated with the existence of several vibronic modes leading to stabilization. Emission energies calculated for the three stabilized vibronic modes in Ar are centered on the observed emission but exhibit a larger splitting. In Kr they are red of the observed band maximum but occur within the observed band. A curve crossing mechanism is identified which can explain the lack of emission for the strongly stabilized, fourfold symmetry modes in Hg/Xe.

Luminescence of Hg((3)P1) atoms trapped in mixed Ar/Xe matrices containing a small amount of Xe is reported. Broad emission bands, strongly red-shifted from absorption are recorded which are assigned to strong complexes formed between the excited mercury Hg* and xenon atoms. Molecular dynamics calculations are performed on simulated Xe/Ar samples doped with Hg to follow the behavior of Hg* in the mixed rare gas matrices leading to exciplex formation. The role of Xe atoms in the first solvation shell (SS1) around Hg was investigated in detail, revealing the formation of two kinds of triatomic exciplexes; namely, Xe-Hg*-Xe and Ar-Hg*-Xe. The first species exists only when two xenon atoms are present in SS1 with specific geometries allowing the formation of a linear or quasi-linear exciplex. In the other geometries, or in the presence of only one Xe in SS1, a linear Ar-Hg*-Xe exciplex is formed. The two kinds of exciplexes have different emission bands, the most red-shifted being that involving two Xe atoms, whose emission is very close to that observed in pure Xe matrices. Simulations give a direct access to the analysis of the experimental absorption, emission, and excitation spectra, together with the dynamics of exciplexes formation.

Luminescence in the vacuum UV/visible region has been recently recorded for atomic cadmium isolated in the rare gas solids Ne, Ar, Kr, and Xe, and because of the availability of diatomic Cd·RG and RG·RG pair potentials, theoretical calculations are now performed and compared to the recorded luminescence spectra. Calculations were first done for the gas-phase excited-state cluster species Cd(1P1)·RGn, where n is the number of rare gas atoms in the cluster. The Cd·RG4, Cd·RG5, and Cd·RG6 clusters showed energy minima for the Cd pz orbital situated at the center of the planar rare gas clusters. With the rare gas distances in the planar clusters fixed at the rare gas dimer bond lengths, the cluster showing the greatest stabilization was the Cd·RG5 species. The cluster calculations were then extended into the solid state for Cd occupying a single substitutional site of the solid rare gas lattice. Two vibronic modes lead to a preferential interaction between the guest and four rare gas atoms, thereby reducing the excited-state energy and leading to distinct minima. The modes are (a) the “body” mode (Q2), which involves the motion of the Cd atom toward an octahedral interstitial site and (b) the “waist” mode (Q3), which involves the in-phase contraction of four rare gas atoms in a single plane toward the Cd atom. Calculations based on single substitutional site occupancy of Cd in the rare gases indicate excited state stabilization for the waist mode for all hosts except neon. The body mode exhibits stabilization in Kr and Xe only. The pair of singlet emission bands observed in the Cd/Kr system is identified as originating from the stabilization of both vibronic modes in the excited state. The lack of stabilization for either mode in Ne, even though singlet emission exists in Cd/Ne, is indicative that a multivacancy site occupancy is likely here.

The excited Ca(4s4dδ 3DJ)RG[3Δ1,2] states (RG=Ar, Kr, Xe) have been characterized spectroscopically by R2PI (resonance-enhanced two-photon ionization) spectroscopy. The main vibrational progressions, assigned to Ca(4s4dδ 3D1)RG[3Δ1]←Ca(4s4pπ 3P0)⋅RG[3Π⎯0] transitions, have weak subbands 3.7±0.5 cm−1 to the blue which have been assigned to analogous transitions to the 3Δ2 upper states. For CaAr and CaKr, rotational analysis has confirmed this assignment. The 3Δ2/3Δ1 splitting is within experimental error the value expected if the molecular spin-orbit coupling constant is derived entirely from the Ca(4s4d 3DJ) atomic contribution. This indicates that there is no “heavy-atom” mixing of RG(ndδ) character into the wave functions of the CaRG(3Δ) states.

The Zn(4s 2 )·Ne[ 1 Σ + ] and the Zn(4s4pπ)·Ne[ 1 Π 1 ] states have been characterized by laser-induced fluorescence spectroscopy. Bond lengths were determined from simulations of the partially-resolved rotational structure of the 1 Π ← 1 Σ + transitions, while bond strengths were estimated from a Birge–Sponer extrapolation with allowance for consistent errors resulting from similar procedures in the analogous Cd·Ne and Hg·Ne transitions. The van der Waals bonding in these states is discussed briefly and compared to that in the analogous M·RG states, where M=Mg, Zn, Cd, Hg and RG=Ne, Ar, Kr, Xe.

The luminescence spectroscopy of atomic cadmium isolated in the solid rare gases is recorded using pulsed synchrotron radiation excitation of the 5p 1P1←5s 1S0 resonance transition. Steady-state and time-resolved analysis of the ultraviolet (UV) emission bands recorded in the Cd/Ne, Cd/Ar, and Cd/Kr systems allows identification of the associated 227.3, 233.4, and the 241/262 nm bands to the singlet fluorescence of atomic cadmium. The origin of the pair of singlet emission bands at 241 and 262 nm in the Cd/Kr system is ascribed to the coexistence of two nondegenerate minima on the 5p 1T1u surface. The weak band present in the Cd/Kr system at 326 nm and the intense pair at 324.4 and 329.6 nm in Cd/Xe all have decay times longer than 1 μs and are associated with the triplet transitions of atomic cadmium. Line shape analysis of the near-UV emission pair in Cd/Xe allows a tentative assignment of the narrow 329.6 nm band to the 5p 3P0→5s 1S0 transition. The intensity of the triplet state emission was observed to be enhanced in the heavier rare gases, being completely absent in Ne and Ar, weak in Kr, and the only emission observed in Xe. The efficiency of intersystem crossing in the Cd/RG systems is very similar to that exhibited by the Zn/RG matrix systems. However, the presence of the 5p 3P0→5s 1S0 emission in Cd/Xe resembles the Hg/RG matrix systems, a reflection of the larger spin-orbit splitting in atomic cadmium compared with zinc.

The unusual doubly excited van der Waal’s state, Mg(3pπ3pπ 3PJ)⋅Kr[3Σ−], has been characterized using a laser-vaporization, supersonic-jet source and R2PI (Resonance Two-Photon Ionization) spectroscopy. This state is very strongly bound (De=3966 cm−1) and has a short bond length (Re=2.45 A) compared to its singly excited analogue, Mg(3s3pπ 3PJ)⋅Kr[3Π0−], for which De=267 cm−1 and Re=3.48 A. In fact, this state is even more than twice as strongly bound as the ground-state Mg(3s)+⋅Kr ion, where De=1949 cm−1 and Re≈2.8 A. Possible reasons for the strong van der Waal’s bonding are discussed, and it is concluded that the lack of σ-σ repulsion because there is no Mg(3sσ) valence electron must be a major factor; the similar ionic van der Waal’s state Mg+(3pπ)⋅Kr[2Π], which would be obtained by removing one of the Mg(3pπ) electrons, is even more strongly bound, with De≈7200 cm−1 [J. S. Pilgrim, C. S. Yeh, K. R. Berry, and M. A. Duncan, J. Chem. Phys. 100, 7945 (1994)].

The pair-potentials calculations of McCaffrey and Kerins [J. Chem. Phys. 106, 7885 (1997)] used with success in simulating the emission spectroscopy of the Zn–RG matrix systems are extended to examine the different temporal decay characteristics exhibited at low temperature, T14 K) in which the intensity of the 219 nm band can reversibly be put into the 238 nm band, was examined by generating the (PES) potential-energy surface for coupled Q2×Q3 vibronic modes. The theoretically predicted activation energy barrier is 380 cm−1, which is only in qualitative agreement with the value of 130.6 cm−1 extracted in the kinetics study. Possible reasons for the overestimation in the theoretical value are discussed.

Absorption spectra of thin-film DMZ/Ar samples, prepared by condensing gaseous mixtures of dimethylzinc (DMZ) with argon at 12 K, were recorded in the region of the first dissociative absorptions of DMZ centered in the gas phase at 200 nm. Large blue shifts are observed in the matrix spectra which can be related to the Rydberg-like characteristics of these excited states of DMZ. The photochemistry of DMZ in an argon matrix was investigated either by subjecting samples to undispersed synchrotron irradiation using a quartz filter to select a wavelength range above 155 nm or to wavelength-specific irradiation. Steady-state and time-resolved luminescence spectroscopy of the dissociation products isolated in solid argon indicate the existence of atomic zinc strongly perturbed by a methyl radical in freshly photolyzed samples, which yields truly isolated atomic zinc upon annealing to 33 K. Dissociation threshold measurements indicate a barrier of 25 kcal/mol for direct cage escape of atomic zinc in the Ar lattice. The increased intensity of Zn(3P1)/Ar emission observed in photolyzed DMZ/Ar samples relative to pure Zn/Ar samples is explained in terms of the enhanced ISC of atomic zinc in the presence of hydrocarbon species in the former samples. This has been shown by co-deposition of atomic zinc with Ar doped with CH4 and C2H6.

Steady-state and time-resolved luminescence spectroscopy of atomic zinc isolated in thin film samples of the solid rare gases, prepared by the cocondensation of zinc vapor with argon, krypton, and xenon has been recorded at 6.3 K using synchrotron radiation. Pairs of emission bands result from photoexcitation of the singlet 4p 1P1←4s 1S0 resonance transition of atomic zinc, even in annealed samples. In Zn/Ar the pair of emission bands were observed in the uv at 218.9 and 238 nm and for Zn/Xe in the near-uv at 356 and 399 nm. For the Zn/Kr system two emission bands were observed in the uv region at 239.5 and 259 nm but in addition, a weaker band was present in the near-uv at 315.6 nm. In a given annealed rare-gas host, the excitation profiles recorded for all the emission bands are identical, exhibiting the threefold splitting characteristic of Jahn-Teller coupling in the triply degenerate excited 1P1 state. These excitation profiles are identified as the solid phase equivalent of the 4p 1P1←4s 1S0 resonance transition of atomic zinc occurring at 213.9 nm in the gas phase. Based on their spectral positions and temporal decay characteristics, the emission bands observed in the uv and near-uv spectral regions have been assigned as the singlet and triplet transitions, respectively, of atomic zinc. The origin of the pairs of emission bands is ascribed to the Jahn-Teller coupling between noncubic vibronic modes of the lattice and the excited 4p orbital of the 1P1 state of atomic zinc, resulting in the coexistence of two energy minima. In Zn/Ar, the effects of slow vibrational relaxation in the excited singlet state were evident in the relative intensities and temporal decay profiles of the pair of emission bands. Specifically, the lower energy emission band was favored with excitation of the highest energy component of the threefold split Jahn-Teller absorption band, while the higher-energy emission was favored with excitation of the lowest-energy component. The intensity of the triplet state emission was observed to be enhanced in the heavier rare gases, being completely absent in Ar, weak in Kr, and the only emission observed in Xe.

The luminescence spectroscopy of atomic zinc isolated in the solid rare gases (ZnRG) is compared with theoretical predictions obtained with the use of diatomic Zn·RG potentials. In particular, the existence of pairs of emission bands, both of which are assigned to the same gas-phase electronic transition, is examined with the use of diatomic pair potentials to simulate the potential-energy surfaces of the Jahn-Teller active vibrational modes of Zn in the solid. The close agreement found between theory and experiment indicates the validity of the use of pair potentials in the analysis of matrix zinc spectroscopy. Thus, it allows identification of the high-energy emission bands in the ZnRG systems as arising from motions of the rare-gas atoms surrounding the atomic zinc guest and the lower-energy bands as associated with the motion of the zinc atom into an octahedral interstitial site in the lattice.

This paper deals with our on-going work on the electronic spectroscopy of tetrapyrrole molecules embedded in cryogenic hosts. Under nanosecond laser excitation of free-base tetrabenzoporphin molecules in a nitrogen matrix at 8 K, increasing laser pulse energy results in essential enhancement of the intensity of one or several vibronic emission lines in the fine-structure fluorescence spectrum. Some characteristics of stimulated radiation are realized in the observed intense monochromatic radiation as a result of a transition from the purely electronic S1 level to a vibrational sublevel of the S0 state, corresponding to the excitation of C–C stretching vibrations of tetrapyrrole methane bridges. We also report on persistent spectral hole-burning effects. Hole and antihole formation analysis gives some insight on the photochemical properties of tetrabenzoporphin in a nitrogen matrix.

DFT/B3LYP calculations are used to analyse the occurrence of reverse isotope shift ratios (ISR) in H/D substitution of the free-base tetrapyrroles, in situations where the frequency ratio νH/νD is less than 1. The reverse ISR effect is found to be most evident in the out-of-plane bending modes (b2g and b3u symmetry) involving some N–H motion for the four molecules studied, viz., porphine (H2P), tetraaza-porphine (H2TAP), tetrabenzo-porphine (H2TBP), and phthalocyanine (H2Pc). It was analysed by following the evolution of the normal mode frequencies with incremental variation of the H atom masses from 1 to 2 amu. This method allows direct, unambiguous mode correlations to be established between the light and the heavy isotopologues. When the NH(D) motion is predominant, the H to D frequency evolution decreases in a continuous manner for a particular normal mode. In the case of two modes of the same symmetry and whose frequencies are similar, their frequency evolutions could cross, depending on the extent of NH(D) motion involved in them. The evolution diagrams may show avoided crossings of various extents, which thereby reflects the degree of the NH(D) motion in the modes. The reverse ISR effect is directly correlated to these avoided crossings. Because the isotope shifts are quite small (–1) and occur in the congested 1500–500 cm–1 spectral region, high-resolution methods yielding narrow line transitions are required for experimental analysis. The matrix isolation technique is particularly well suited for this work and is proposed for use in a search for this effect.

The I(2)(D'-A') luminescence in liquid C(7)F(16), C(8)F(18), C(9)F(20), and C(12)F(26) has been observed following irradiation with visible (within the I(2) X → B band region) and UV (λ < 300 nm) lasers. The band is shifted by ~2000 cm(-1) to the red relative to the gas phase and is significantly broader (fwhm ≈ 3000 cm(-1) vs 500 cm(-1) in the gas phase). Two-color excitation of other halogens in C(n)F(2n+2) solvents revealed similarly shifted and strongly broadened D'-A' bands of Br(2), IBr, and BrCl. The stability of the ion-pair states of halogens in room temperature liquids opens new experimental opportunities for condensed phase studies and may be of applied interest considering the increasing industrial applications of perfluorocarbons.

Luminescence spectroscopy of the metal atoms Mg, Zn and Cd isolated in solid neon is recorded using pulsed synchrotron radiation excitation of the ns1np1 1P1-ns2 1S0 resonance (n = 3, 4 and 5 respectively) transitions. Two features, a dominant band and a red-shoulder, are identified in the UV absorption spectra of Zn/Ne and Cd/Ne. Excitation of these features yields distinct emission bands with the red-shoulder absorption producing the smaller, Stokes-shifted emission. Nanosecond decaytime measurements, made with the time correlated single photon counting technique indicate the emission bands arise from the spin singlet 1P1→1S0 transition. Hence, it is concluded that the duplication of absorption and emission features in the Cd/Ne and Zn/Ne systems arises from metal atom occupancy in two distinct sites. In contrast, Mg/Ne luminescence consists of single excitation and emission bands, indicative of occupancy in just one site. The occurrence of distinct photophysical characteristics of the linewidths, Stokes shift and lifetimes in the Mg/Ne system, compared with those recorded for Zn/Ne and Cd/Ne, is rationalized in terms of a different site occupancy for atomic Mg. Accurate interaction potentials for the ground states of the M · Ne diatomics are used to analyse site occupancies and interpret this contrasting behavior.

Absorption and luminescence spectra have been recorded in the 200–700 nm range for atomic magnesium isolated in solid Ar and Kr at 12 K. Strong absorptions occurring in the near UV at 285 nm, showing a threefold splitting, are identified as the solid phase equivalent of the gas phase 3p 1P1←3s 1S0 Mg atom transition. Evidence of multiple site trapping of Mg atoms in Ar and Kr matrices formed at 12 K has been obtained from annealing studies in absorption, but especially in luminescence spectroscopy. The single emission band of Mg/Ar, centered at 297.6 nm, exhibits a radiative lifetime of 1.12 ns and is thereby assigned as singlet 3p 1P1→3s 1S0 Mg atom fluorescence. The luminescence exhibited by the Mg/Kr system is more complex than the Mg/Ar system in that a weak visible band at 472 nm occurs as well as several bands in the UV having nanosecond lifetimes. The richness of the Mg/Kr UV spectra has been examined with annealing and time‐resolved measurements and identified as arising from multiple trapping sit...

Laser‐induced fluorescence (LIF) measurements of the Mg(3s3p 1P1)⋅Xe(1Π1) ←Mg(3s3s 1S0)⋅Xe(X 1Σ+) transition of the jet‐cooled MgXe complex have revealed that the ground X 1Σ+ state is quite weakly bound (De‘ ≊ 100 cm−1) compared to the 1Π1 excited state (De’ ≊ 1500 cm−1), and that the bond length in the 1Π1 excited state is some 1.5 A shorter. Here we report the observation of dispersed fluorescence spectra from single vibrational levels of the 1Π1 state, consisting mainly of oscillatory bound–free continua which extend over some 7500 cm−1. These spectra are analyzed using the semiclassical method of Child and LeRoy to determine the repulsive portion of the Mg⋅Xe(X 1Σ+) interaction potential up to nearly 1 eV in energy. Attempts were made to fit the experimental potential curves to several simple analytical functions, with a two‐term Buckingham‐type function yielding the best representation. A comparison of the repulsive portion of the Mg⋅Xe(X 1Σ) potential curve with that of the analogous Na⋅Xe(X 2Σ) cu...

Site-selective excitation has been used to simplify complex emission recorded in the visible spectral region for atomic europium isolated in the solid rare gases. In addition to y8P resonance fluorescence, excitation of the y8P state produces emission from the z6P state and the metastable a10D state. Very weak emission at 690 nm is tentatively assigned to the J = 9/2 level of the z10P state. Eu atoms isolated in the red and blue sites exhibit very different temperature dependence both spectrally and temporally. For the y8P state emission the red site atoms exhibit small Stokes shifts and yield radiative lifetimes while the emission from the blue site loses intensity and the temporal profiles shorten dramatically between 10 and 16 K indicating very efficient non-radiative relaxation in this site. An analysis of the Stokes shifts exhibited for the y8P state in each site supports the attributions made in a previous publication [O. Byrne and J.G. McCaffrey, J. Chem. Phys. 134, 124501 (2011)]10.1063/1.3564947 that the smaller blue tetravacancy site has a greater repulsive interaction with the guest. With the exception of the y8P state resonance fluorescence, the recorded decay profiles of all the other emissions exhibit multiple components. This behaviour has been attributed to the existence of multiple crystal field levels arising from the splitting of the distinct spin-orbit levels from which emission occurs.

Laser induced fluorescence (LIF) excitation spectra recorded for the vibrational bands in the Mg(3s3p 1P1)⋅Xe(1Π1)←Mg(3s3s 1S0)⋅Xe (X 1Σ+) system have been analyzed, yielding absolute vibrational assignments and values of ωexe=1.585±0.02 and ωe=97.5±1.0 cm−1 for the 1Π1 state of 24Mg132Xe. From a Birge–Sponer extrapolation, the well depth of this state is estimated to be 1500 cm−1. Simulations of rotationally structured spectra of three of the most intense vibrational bands are consistent with R‘e=4.56±0.12 A for the X 1Σ+ state. From Morse function extrapolation of the excited state rotational constants from the simulations, and Franck–Condon intensity simulations of the 1Π1←X 1Σ+ vibrational progressions, R’e for the 1Π1 state is estimated to be 3.07±0.10 A. The 1Π1 state of MgXe fluoresces strongly. The corresponding 1Π1 states of ZnXe and CdXe do not fluoresce, but ‘‘action’’ spectra from the production (via predissociation) of metal atom 3PJ states are observed. Possible reasons for these differences...

A structureless band observed at 180 nm in the absorption and excitation spectra of Cl2/Ar matrices is tentatively assigned as the spin forbidden 3Σ+u ← X 1Σ+g transition of molecular chlorine. Having an absorption cross section of approximately 10−18 cm2 in the solid, a twofold order of magnitude increase in the transition probability is observed relative to the gas phase. Wavelength specific measurements of the photodissociation of molecular chlorine in crystalline argon samples showed that a dominant threshold exists in the 130 nm band at 9.2 eV corresponding to absorption into the bound 1 1Σ+u state. The maximum quantum yield for permanent dissociation in the 130 nm band was found to be 0.3. Luminescence evidence indicates that this dissociation does not involve a charge‐transfer mechanism but a crossing from the bound 1 1Σ+u state to a repulsive potential on which an impulsive cage escape occurs. Photoexcitation in the 180 nm band also results in the permanent dissociation of chlorine as well as the ...

Narrow excitation features present on the [Ar]3d64s1a6D(J = 9/2−1/2)←[Ar]3d54s2a6S1/2 transitions of manganese atoms isolated in solid Kr are analyzed within the framework of weak crystal field splitting. Use of the Wp optical lineshape function allowed identification of multiple zero-phonon lines for individual spin-orbit J states of the a a6D←a6S transition recorded with laser-induced excitation spectroscopy. Excellent agreement exists between the predicted crystal field splitting patterns for the J levels of the a6D state isolated in the «red» tetravacancy site of solid Kr. The tetrahedral crystal field of the «red» trapping site splits J>3/2 levels of the a6DJ and a4D7/2 states by approximately 30 cm−1. This report represents the first definitive evidence of crystal field splitting, induced by the weak van der Waals interactions between a neutral metal atom and the rare gas atoms surrounding it in a well-defined solid-state site.

Narrow linewidth emission features observed in the near-UV following y (6)P state excitation of atomic manganese isolated in the solid rare gases are assigned to b (4)D and a (4)P states. These states arise from the 3d(5)4s(2) electronic configuration, identical to that of the (6)S ground state, and the origin of the narrow linewidths. Two thermally stable sites, labeled blue and red on the basis of their position in absorption spectra, are occupied by atomic Mn in Ar and Kr while a single site is present in Xe. The red site produces a single, narrow line emission for the b (4)D state at 329 nm. In contrast, a lineshape analysis of the complex blue site b (4)D state emission between 331 and 332 nm reveals the occurrence of three zero phonon lines (ZPLs). Millisecond emission decay curves recorded for these features are found to be complex, requiring double and triple exponential fit functions. The origins of the complex decays and multiple ZPLs are shown to arise from weak crystal field splitting (CFS) of the J=7/2 spin-orbit level of the b (4)D state of atomic Mn isolated in the blue site of the solid rare gases. Fields of cubic symmetry are capable of inducing splitting for J>3/2 so atoms isolated in both single vacancy and tetravacancy sites in the fcc lattices of the solid rare gases are prone to this effect. b (4)D state emission is also produced following y (6)P excitation for Mn atoms occupying the red sites in Ar and Kr. However, Mn atoms isolated in the larger tetravacancy sites have small matrix shifts and do not exhibit any CFS. The magnitudes of the weak CF splittings are shown to depend on both the excited state electronic configurations 3d(5)4s(2) b (4)D and 3d(6)4s(1) a (4)D states and the size of the matrix site occupied by atomic Mn.

We have observed the time dependence of the motion of the atoms in a van der Waals complex (HgAr). This motion leads to direct dissociation or corresponds to vibrations in the potential well. The time evolution is similar to that observed in the femto-second domain for chemically bound molecules, i.e. it leads to appearance of transients and vibrational recurrences. In softening the potentials, the characteristic time for the movements of the atoms is slowed down to the picosecond. We have observed and analyzed the direct dissociation and the vibrational recurrences in the B potential well.

The photodissociation of Cl2 in crystalline Xe is examined using synchrotron radiation for all state of Cl2 from the C 1Π1u state to the region of Xe exciton absorption. Isolation of atomic chlorine in two dominant trapping sites is observed following photodissociation throughout the spectral region studied. The production efficiency of the thermally stable trapping site was found to increase significantly with temperature and was most pronounced in the region of the onset of the Xe2Cl excitation feature. Correlation between these two processes is explained in terms of a charge‐transfer‐induced dissociation mechanism involving the formation of a Xe+(Cl2)− intermediate. In contrast to Ar and Kr matrices, photodissociation of Cl2 in Xe appears to occur without a pronounced cage effect. This observation is rationalized in terms of the larger lattice parameters of Xe which allows isolation of Cl2 and Cl at single substitutional and octahedral interstitial sites, respectively. From this structural information,...

A simple spreadsheet program is presented that can be used by undergraduate students to calculate the lattice-site distributions in solids. A major strength of the method is the natural way in which the correct number of ions or atoms are present, or absent, at specific lattice distances. The expanding-cube method utilized is straightforward to set up in a spreadsheet and is easily adapted for the prediction of highly accurate Madelung constants. Calculations performed out to the 10th cube return a value for the Madelung constant exact to 5 decimal places. From an educational point of view, the method presents students the possibility of directly observing the difference between doing a "crude" lattice-sum calculation compared to what results under the "zero-net charge" condition. Caveats, such as truncation errors that must be considered by students when comparing the results of their limited cube calculations with literature pair-distribution functions, are also encountered. The pair distribution function of the van der Waals solid formed by condensed krypton atoms is selected for comparison with that of NaCl since the unit cells of these two solids have the same lattice parameters.

Rydberg series observed in the excitation spectra of Cl and H atoms isolated in the rare gas (Rg) crystals Kr and Xe are associated with the charge transfer species Cl−Rg+ and H−Rg+. The progressions originate from hole states of Rg+ which converge to the top of the rare gas valence band in an analogous manner to the convergence of conventional exciton states to the bottom of the conduction band. A model based on the effective mass approximation and a quantum defect concept predicted such progressions in Xe and Kr crystals and it is supported by the present results.

A structureless band observed at 180 nm in the absorption and excitation spectra of Cl2/Ar matrices is tentatively assigned as the spin forbidden 3Σ+u ← X 1Σ+g transition of molecular chlorine. Having an absorption cross section of approximately 10−18 cm2 in the solid, a twofold order of magnitude increase in the transition probability is observed relative to the gas phase. Wavelength specific measurements of the photodissociation of molecular chlorine in crystalline argon samples showed that a dominant threshold exists in the 130 nm band at 9.2 eV corresponding to absorption into the bound 1 1Σ+u state. The maximum quantum yield for permanent dissociation in the 130 nm band was found to be 0.3. Luminescence evidence indicates that this dissociation does not involve a charge‐transfer mechanism but a crossing from the bound 1 1Σ+u state to a repulsive potential on which an impulsive cage escape occurs. Photoexcitation in the 180 nm band also results in the permanent dissociation of chlorine as well as the ...

Structured progressions, assocd. with the Cl-Rg+ and H-Rg+ charge transfer species, are obsd. for Cl and H atoms isolated in Kr and Xe (Rg) crystals and are assigned as transitions to Rydberg states. The Rydberg levels correspond to delocalized pos. hole states in the rare gas solid (Rg+) orbiting a neg. center (Cl- or H-). For OH in Ar and Kr matrixes, transitions to static charge transfer states are identified. For both of these rather extreme situations, simple model are used successfully to predict the transition energies. For the former, an exciton model based on the effective mass approxn. and utilizing quantum defect nos. is used, while in the latter, a Coulombic potential screened by the medium is used. [on SciFinder (R)]

Laser induced fluorescence spectroscopy of free-base (H(2)Pc) and zinc (ZnPc) phthalocyanines trapped in rare gas and nitrogen matrices reveals a quite unexpected phenomenon with a moderate increase in the laser intensity. In all matrices except Xe, a huge increase occurs in the intensity of an emission band near 755 nm when pumping the S(1)

The metastable a(3Π0−) and A(3Π0+) states of the Mg(3s3p)Ar molecule were synthesized in a free‐jet expansion of metastable Mg(3PJ) atoms, produced by the laser vaporization of a magnesium rod, in pure Ar. The a(3Π0−), A(3Π0+), and E(3∑+) states were characterized spectroscopically by laser‐induced fluorescence. The 3Π(v=0) states were found to be very near the Hund’s case (a) limit, with only 0.31 cm−1 separating the 3Π0+ and 3Π0− levels. The internuclear separations, re, were found to be 3.63 A and the dissociation energies 316 and 296 cm−1, respectively. The E(3∑+) state is quite deeply bound (1128 cm−1) with a much smaller re, 2.83 A, and it is postulated that the Ar atom has substantially penetrated the outer lobe of the 4s Rydberg orbital of the Mg(3s4s 3S1) atomic state to which this state correlates. Despite large populations of both Mg(3P1) and Mg(3P2), neither the 3Π1 nor 3Π2 states of MgAr were observed, apparently because the molecular 3Π1,2 states are collisionally quenched to the lower‐ene...

Rab11-FIP3 is an endosomal recycling compartment (ERC) protein that is implicated in the process of membrane delivery from the ERC to sites of membrane insertion during cell division. Here we report that Rab11-FIP3 is critical for the structural integrity of the ERC during interphase. We demonstrate that knockdown of Rab11-FIP3 and expression of a mutant of Rab11-FIP3 that is Rab11-binding deficient cause loss of all ERC-marker protein staining from the pericentrosomal region of A431 cells. Furthermore, we find that fluorophore-labelled transferrin cannot access the pericentrosomal region of cells in which Rab11-FIP3 function has been perturbed. We find that this Rab11-FIP3 function appears to be specific because expression of the equivalent Rab11-binding deficient mutant of Rab-coupling protein does not perturb ERC morphology. In addition, we find that other organelles such as sorting and late endosomes are unaffected by loss of Rab11-FIP3 function. Finally, we demonstrate the presence of an extensive coiled-coil region between residues 463 and 692 of Rab11-FIP3, which exists as a dimer in solution and is critical to support its function on the ERC. Together, these data indicate that Rab11-FIP3 is necessary for the structural integrity of the pericentrosomal ERC.

International audience; Laser-induced excitation spectra recorded for the electric-quadrupole 3d(6)4s a(6)D(J) a(6)S(5/2) transition at 585.75 nm. The identified matrix-shift of +20 cm(-1) allows an assessment of the extent of the ground state stabilization in the red (2 degrees) site of atomic Mn isolation in solid Kr. Emission produced with direct a(6)D state excitation yielded both the 585.75 and 626 nm features. The former band arises for Mn atoms occupying the red site-the latter from blue site occupancy in solid Kr. The excitation linewidths recorded for these two sites differ greatly, with the blue site yielding a broad featureless profile, in contrast to the narrow, structured features of the red site. The corresponding red site a(6)D(J) a(6)S(5/2) transitions in Ar and Xe matrices are broader than in Kr-a difference considered to originate from the site sizes available in these hosts and the interatomic Mn center dot RG potentials. The millisecond decay times recorded for the red emission bands in the Mn/RG systems are all much shorter than the 3 s value predicted for the gas phase a(6)D(9/2)-> a(6)S(5/2) transition. This enhancement allows optical pumping of the forbidden a(6)D(J) a(6)S transitions with low laser powers when atomic manganese is isolated in the solid state. However all the emission decays are complex, exhibiting triple exponential decays. This behavior may be related to the dependence of the excitation linewidths on the J value, indicating removal of the J degeneracy due to weak matrix-induced, crystal field splitting.

International audience; The relaxation of electronically excited atomic manganese isolated in solid rare gas matrices is observed from recorded emission spectra, to be strongly site specific. z P-6 state excitation of Mn atoms isolated in the red absorption site in Ar and Kr produces narrow a D-4 and a D-6 state emissions while blue-site excitation produces z P-6 state fluorescence and broadened a D-4 and a D-6 emissions. Mn/Xe exhibits only a single thermally stable site whose emission at 620 nm is similar to the broad a D-6 bands produced with blue-site excitation in Ar and Kr. Thus in Ar(Kr), excitation of the red site at 393 (400) nm produces narrow line emissions at 427.5 (427.8) and 590 (585.7) nm. From their spectral positions, linewidths, and long decay times, these emission bands are assigned to the a D-4(7/2) and a D-6(9/2) states, respectively. Excitation of the blue site at 380 (385.5) nm produces broad emission at 413 (416) nm which, because of its nanosecond radiative lifetime, is assigned to resonance z P-6 -> a S-6 fluorescence. Emission bands at 438 (440) and 625 (626.8) nm, also produced with blue-site excitation, are broader than their red-site equivalents at 427.5 and 590 nm (427.8 and 585.7 nm in Kr) but from their millisecond and microsecond decay times are assigned to the a D-4 and a D-6 states. The line features observed in high resolution scans of the red-site emission at 427.5 and 427.8 nm in Mn/Ar and Mn/Kr, respectively, have been analyzed with the W-p optical line shape function and identified as resolved phonon structure originating from very weak (S=0.4) electron-phonon coupling. The presence of considerable hot-phonon emission (even in 12 K spectra) and the existence of crystal field splittings of 35 and 45 cm(-1) on the excited a D-4(7/2) level in Ar and Kr matrices have been identified in W-p line shape fits. The measured matrix lifetimes for the narrow red-site a D-6 state emissions (0.29 and 0.65 ms) in Ar and Kr are much shorter than the calculated (3 s) gas phase value. With the lifetime of the metastable a D-6(9/2) state shortened by four orders of magnitude in the solid rare gases, it is clear that the probability of the "forbidden" a D-6 -> a S-6 atomic transition is greatly enhanced in the solid state. A novel feature identified in the present work is the large width and shifted D-4 and D-6 emissions produced for Mn atoms isolated in the blue sites of Ar and Kr. In contrast, these states produce narrow, unshifted (gas-phase-like) D-4 and D-6 state emissions from the red site.

International audience; This study collects information from absorption and luminescence excitation spectra recorded for Mn atoms isolated in the solid rare gases Ar, Kr, and Xe and presents an analysis of the site occupancy, based on the polarizabilities of the rare gases and the observed spectral shifts. Two thermally stable sites of isolation exist for atomic Mn in solid Ar and Kr, while a single thermally stable site is present in Mn/Xe. Site occupancy assignments are based on the application of a polarizability model to the z P-6(5/2)

Multicomponent emission bands are recorded for the 3P1→1S0 transition of atomic mercury isolated at single sites in solid Ar, Kr, and Xe matrices. A blueshift observed at elevated temperatures on the 273 nm emission of Hg/Xe is identified in line shape analysis as arising from decreasing intensity of the central component in the band profile. The origin of the multiple components in the emission bands is ascribed to the existence of several vibronic modes which lead to excited state stabilization in the Hg(3P1)/RG matrix systems. A detailed description of these modes and their energetics is presented in the paper directly following. Photoexcitation of the 3P1 state also yields small amounts of 3P0 state emission. Hg atom 3P1 to 3P0 state intramultiplet relaxation (IMR) is most efficient in Hg/Xe where the ratio of this relaxation channel to 3P1 state radiative decay is 1/200 as established in time-integrated emission spectra. Despite the weakness of IMR, pulsed laser excitation combined with photon counting detection provide time-gated 3P0 state emission spectra largely free of the more intense 3P1 state emission. Such emission spectra recorded under high resolution for the 3P0→1S0 transition of atomic mercury isolated in solid Xe provide the first example of the occurrence of a zero-phonon lines for a metal atom isolated in a rare gas matrix. Wp line shape analysis conducted on the emission bands recorded at specific temperatures, confirm this assignment. The electron–phonon coupling strength (Huang-Rhys, S factor) extracted in the line shape fits for the Hg/Xe transition is 1.3. Slightly stronger coupling is identified in Kr (S=2.2) and stronger still in Ar (S=3.3). Analysis of the diatomic Hg⋅RG potential energy curves reveal that the origin of the weak electron–phonon coupling lies primarily in the similarity in the ground and excited states, but also indicates the site size offered by the host solid plays a role.

Irradiation of atomic europium isolated in the solid rare gases, with low intensity laser excitation of the y(8)P←a(8)S resonance transition at ca. 465 nm, is found to produce singly charged europium cations (Eu(+)) in large amounts in xenon and in smaller amounts in argon. Confirmation of the formation of matrix-isolated Eu(+) is obtained from characteristic absorption bands in the UV and in the visible spectral regions. The luminescence produced with excitation of the cation bands is presented in greatest detail for Eu/Xe and assigned. Excitation of the 4f(7)((8)S7/2)6p3/2 absorption bands of Eu(+) between 390 and 410 nm produces emission which is quite distinct from that resulting from excitation of the 4f(7)((8)S7/2)6p1/2 absorption (430 to 450 nm) features. The latter consists of narrow, resolved emission bands with Stokes shifts ten times smaller than the former. The observed spectral differences are discussed in relation to the different spatial symmetries of the p3/2 and p1/2 orbitals in these j-j coupled (7/2, 3/2)J and the (7/2, 1/2)J levels. Møller-Plesset calculations are conducted to obtain the molecular parameters of the neutral Eu-RG and cationic Eu(+)-RG diatomics (RG = Ar, Kr, Xe). From the short bond lengths and the strong binding energies obtained for the Eu(+)-RG species, these values suggest the isolation of the ion in small, possibly interstitial sites especially in xenon. In contrast, but consistent with previous work [O. Byrne and J. G. McCaffrey, J. Chem. Phys. 134, 124501 (2011)], the interaction potentials calculated herein for the Eu-RG diatomics suggest that the neutral Eu atom occupies tetra-vacancy (tv) and hexa-vacancy (hv) sites in the solid rare gas hosts. Possible reasons for the facile production of Eu(+) in the solid rare gases are discussed. The mechanism proposed is that atomic europium is also acting as an electron acceptor, providing a temporary trap for the ionised electron in the matrices.

A concentration study is used to identify the optical absorption of zinc atoms isolated in solid nitrogen. Photoexcitation of the threefold-split, atomic 4p 1P1 singlet absorption band did not produce any emission from either the singlet or triplet states. Hartree–Fock (relativistic effective core potentials) plus variational and multireference perturbational configuration-interaction calculations are performed to analyze this very efficient quenching of excited state atomic zinc by molecular nitrogen. Of the two geometries considered in energy calculations of the approach of Zn(1P1) to N2, the collinear exhibited a slightly greater stabilization than the perpendicular approach. However, the collinear is identified as of no significance in the excited state quenching due to the absence of low energy crossings with the ground state. In contrast, for the perpendicular approach a crossing between the repulsive ground 1A1(1S0) state and the strongly attractive 1B2(1P1) state occurs close to the energy minimum of the 1B2 state. The efficiency of crossing between these states is analyzed in the framework of one-dimensional Landau–Zener (LZ) theory. A hopping probability of 0.07 is obtained for a single crossing, considered important in a rapidly relaxing solid state system, such as present in a low temperature matrix. Crossings found between the repulsive 3B1(3P1) and 3A1(3P1) states with the strongly bound 1B2(1P1) state are expected to play a role in gas phase Zn(1P1) quenching leading to the production of Zn(3PJ) states. LZ calculations indicate a small hopping probability for these crossings, consistent with the small 1P1→3PJ quenching cross sections observed in the gas phase work.

Previous steady-state and time-resolved luminescence spectroscopy of 3p ¹P₁ atomic magnesium, isolated in thin film samples of the solid rare gases, has been extended to include the higher energy 4p ¹P₁ excitation. Well resolved site splittings have been recorded in Mg/Ar samples for excitation to the 4p ¹P₁ level. A small red shift in the absorption energy to the 4p ¹P₁ level for Mg/Ar contrasts with a small blue shift on absorption to the 3p ¹P1 level. Direct emission from the 4p ¹P1 level is not observed in any of the rare gas matrices, instead intense emission from the low energy 3p ¹P1 level is. Measurements of the emission decay curves in Mg/Ar have revealed slow rates in the steps feeding the 3p ¹P₁ level following 4p ¹P₁ excitation. The reason for the differential shifting of the 4 p ¹P₁ and 3p ¹P₁ levels as well as the lack of direct 4p ¹P₁ emission is thought to be related to the strong binding interaction between Mg in the 4p ¹P₁ state and the rare gases.

The weakly bound Ca(4s4dσ 3D3)⋅Ar[3Σ+] state has been characterized by means of R2PI (Resonant Two-Photon Ionization) spectroscopy, using transitions from the Ca(4s4pπ 3P0)⋅Ar[3Π0−] metastable state prepared in a laser-vaporization/supersonic jet source. Because several of the vibrational levels are above the dissociation limit [to Ca(4s4d 3D3)+Ar(1S0)], it is concluded that there must be a substantial maximum in the Ca(4s4dσ 3D3)⋅Ar[3Σ+] potential curve (>200 cm−1) at large R (>4.0 A). This is discussed, and shown to be consistent with our earlier ideas of “penetration” of outerlobes of electron density of metal atom excited states by RG (rare-gas) atoms. Perturbations observed, due to possible potential curve crossings with states of different electronic symmetry, are also discussed.

The photodissociation of dimethylmercury, Hg(CH3)2, in dilute argon matrixes is induced efficiently by ArF (193 nm) and inefficiently by KrF (248 nm) laser irradiation. The reaction products are identified by their IR absorption and UV absorption and luminescence spectra. Upon ArF photolysis, ethane remaining in close proximity of a Hg atom (Hg‚C2H6) is the main reaction product. The Hg‚C2H6 complex is destroyed by KrF radiation with formation of HHgC2H5, which is photolyzed, giving HgH2 and ethylene. Unidentified near UV emission bands recorded during irradiation are tentatively assigned to an unstable Hg‚CH3 complex.

The mechanism of 4p 1P1→4p 3PJ intersystem crossing (ISC) following excitation of the 4p 1P1 level of matrix-isolated atomic zinc is investigated using a pair potentials approach. This is achieved by extending earlier ISC calculations on the Zn⋅RG2 and Zn⋅RG3 complexes to the square planar Zn⋅RG4 and square pyramidal Zn⋅RG5 species which are the building blocks of the Zn⋅RG18 cluster used to represent the isolation of atomic zinc in the substitutional site of a solid rare-gas host. ISC predictions in these clusters are based on whether crossing of the strongly bound 1A1 states, having a 4p 1P1 atomic asymptote, occurs with the repulsive 3E states correlating with the 4p 3PJ atomic level of atomic zinc. Predictions based on 1A1/3E curve crossings for 3E states generated with the calculated ab initio points for the Zn⋅RG 3Σ(pz) states do not agree with matrix observations. Based on similar overestimation of ISC in the Zn⋅RG diatomics, less repulsive Zn⋅RG 3Σ(pz) potential curves are used resulting in excellent agreement between theory and observations in the Zn–RG matrix systems. 1A1/3E curve crossings do not occur in the Zn–Ar system which shows only singlet emission. Curve crossings are found for the Zn–Xe system which exhibits only triplet emission. The Zn–Kr system does not show a crossing of the body mode Q2, which exhibits a strong singlet emission at 258 nm while the waist mode Q3, does have a crossing, resulting in a weak singlet emission at 239 nm and a stronger triplet emission at 312 nm. The efficiency of ISC is determined from Landau–Zener estimates of the surface hopping probabilities between the 1A1 and the 3E states. Differences in the application of this theory in the gas and solid phase are highlighted, indicating that the rapid dissipation of the excited-state energy which occurs in the solid must be included to obtain agreement with observations.

The temperature dependence of the pairs of emission bands present for atomic zinc isolated in annealed solid argon, krypton, and xenon samples is examined in steady-state and time-resolved luminescence spectroscopy. The pairs of emission bands in all the Zn/RG systems exhibited a reversible temperature dependence whereby the intensity of the high-energy band decreased, while the low-energy band gained in intensity with increasing temperature. In the Zn/Ar system, the decrease in the intensity of the 218.9 nm emission band observed between 9 and 28 K was coupled with a concomitant increase in the intensity of the band at 238 nm. In this temperature range the decay times of the 218.9 nm band decreased while the 238 nm band exhibited a constant decay time of 1.41 ns and a rise time correlated with the decay of the 218.9 nm band. The interdependence exhibited by the intensities and decay times of the two emission bands is modeled by an activated nonradiative process with a barrier height of 130.6 cm−1 for population interconversion between the pairs of emitting levels on of the spin singlet adiabatic potential energy surface. Similar behavior was observed in Zn/Kr between 6.3 to 20 K, but at higher temperatures this system also exhibited enhanced intersystem crossing. Likewise, for Zn/Xe, the low-energy 399 nm emission increased in intensity at the expense of the high-energy 356 nm emission up to a temperature of 40 K. For the Zn/Kr pair of singlet emissions and the Zn/Xe pair of triplet emissions, barrier heights of 78.1 and 42.6 cm−1 were evaluated, respectively.