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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.

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.

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.

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.

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)

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.

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.

The IR spectroscopy of matrix-isolated DMZ is presented as a precursor for the analysis of DMZ photochemistry in the solid rare gases. In agreement with gas-phase work, the present study reassigns the band observed at 1309.2 cm-1, currently assigned in the matrix literature to the bending mode of the impurity methane, to the ν10 + ν14 band combination mode of DMZ. From a combination of IR absorption and UV luminescence studies, atomic zinc and a pair of methyl radicals (Zn + 2CH3) are identified as the photochemical products formed with ArF excimer laser photolysis. A concerted dissociation pathway of DMZ in solid Ar is considered to be the only mechanism leading to the production of methyl radicals in the vicinity of ground-state atomic zinc. The lack of observation of the methylzinc (CH3Zn) and methyl radicals as products is explained in terms of the rapid geminate recombination of these radicals in the matrix cage, which in turn explains the poor efficiency of DMZ dissociation in the solid. Evidence exists for the formation of secondary products with ArF photolysis, namely, the production of ethylzinc hydride and acetylene. It is proposed that the former arises from the excited-state insertion of atomic zinc into the C−H bonds of the small amounts of ethane arising from the recombination of the methyl radicals. Acetylene is a product of ArF dissociation of ethylene which results from recombination of hot methyl radicals.

Steady-state and time-resolved emission spectroscopy of the A-X system of Cl2 is used to distinguish molecular chlorine isolated as monomers and clusters in solid argon samples. The lifetime of the metastable A' 3-PI-2u state is measured to be an order of magnitude less, when chlorine is present as clusters, than when it is truly isolated. Photodissociation of molecular chlorine clusters was found to be insignificant as monitored by the emission of Ar2Cl at 260 nm. Measurement of the dissociation threshold of molecular chlorine in the 9 eV region as a function of temperature showed little variation. Using spectroscopic data it is concluded that dissociation is occurring by an impulsive mechanism involving curve-crossing from the initially populated Ar+ (Cl2)- charge transfer state to repulsive potentials correlating with ground state atomic chlorine and not via a harpooning mechanism. A simple microscopic model, drawn from experimental data and pairwise addition of ArCl potential terms, is constructed to describe the steps involved in this dissociation process in the solid lattice.