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Isolated mixed-ligand complexes provide tractable model systems in which to study competitive and cooperative binding effects as well as controlled energy flow. Here, we report spectroscopic and isotopologue-selective infrared photofragmentation dynamics of mixed gas-phase Au(12/13CO)n(N2O)m+ complexes. The rich infrared action spectra, which are reproduced well using simulations of calculated lowest energy structures, clarify previous ambiguities in the assignment of vibrational bands, especially accidental coincidence of CO and N2O bands. The fragmentation dynamics exhibit the same unexpected behaviour as reported previously in which, once CO loss channels are energetically accessible, these dominate the fragmentation branching ratios, despite the much lower binding energy of N2O. We have investigated the dynamics computationally by considering anharmonic couplings between a relevant subset of normal modes involving both ligand stretch and intermolecular modes. Discrepancies between correlated and uncorrelated model fit to the ab initio potential energy curves are quantified using a Boltzmann sampled root mean squared deviation providing insight into efficiency of vibrational energy transfer between high frequency ligand stretches and the softer intermolecular modes which break during fragmentation. [ABSTRACT FROM AUTHOR]

The article focuses on the discussion of scattering phenomena involving larger molecules, specifically addressing questions related to the phenylethynyl radical in the interstellar medium. Topics include the challenges in detecting the phenylethynyl radical due to its complex spectrum, potential formation mechanisms in space, and the role of experimental and computational methods in predicting its presence.

The article focuses on a general discussion of scattering phenomena at condensed-phase surfaces, particularly in relation to the challenges and techniques involved in measuring angular distributions of evaporating atoms. Topics include the difficulties of measuring angular distributions from cylindrical jets versus flat jets, the prediction of helium atom evaporation patterns, and the observation of surfactant segregation in microjets.

The article focuses on a general discussion about the scattering of larger molecules, particularly examining the differences in potential energy surfaces (PES) between HDO, H2O, and D2O. Topics include the reason for stronger back scattering in HDO compared to H2O and D2O, the role of symmetry and potential terms in scattering phenomena, and specific insights into the n10 term affecting back-scattering.

We report a combined experimental and computational study of carbon dioxide activation at gas-phase Ho+ and HoO+ centres. Infrared action spectra of Ho(CO2)n+ and [HoO(CO2)n]+ ion–molecule complexes have been recorded in the spectral region 1700–2400 cm−1 and assigned by comparison with simulated spectra of energetically low-lying structures determined by density functional theory. Little by way of activation is observed in Ho(CO2)n+ complexes with CO2 binding end-on to the Ho+ ion. By contrast, all [HoO(CO2)n]+ complexes n ≥ 3 show unambiguous evidence for formation of a carbonate radical anion moiety,. The signature of this structure, a new vibrational band observed around 1840 cm−1 for n = 3, continues to red-shift monotonically with each successive CO2 ligand binding with net charge transfer from the ligand rather than the metal centre. [ABSTRACT FROM AUTHOR]

Infrared multiple-photon dissociation spectroscopy has been applied to study Ptn(N2O)+ (n = 1–8) clusters which represent entrance-channel complexes on the reactive potential energy surface for nitrous oxide decomposition on platinum. Comparison of spectra recorded in the spectral region 950 cm−1 to 2400 cm−1 with those simulated for energetically low-lying structures from density functional theory shows a clear preference for molecular binding via the terminal N atom, though evidence of O-binding is observed for some cluster sizes. Enhanced reactivity of Ptn+n ≥ 6 clusters towards N2O is reflected in the calculated reactive potential energy surfaces and, uniquely in the size range studied, Pt6(N2O)+ proved impossible to form in significant number density even with cryogenic cooling of the cluster source. Infrared-driven N2O decomposition, resulting in the formation of cluster oxides, PtnO+, is observed following vibrational excitation of several Ptn(N2O)+ complexes. [ABSTRACT FROM AUTHOR]

Velocity map imaging has been employed to study multi-photon fragmentation of vanadium monoxide (VO) via the C 4Σ− state. The fragmentation dynamics are interpreted in terms of dissociation at the three-photon level, with the first photon weakly resonant with transitions to vibrational energy levels of the C 4Σ− state. The dissociation channels accessed are shown to depend strongly on the vibrational level via which excitation takes place. Analysis of the evolution of the kinetic energy release spectrum with photon energy leads to a refined value for the dissociation energy of ground state VO of D0(VO) = 53 126 ± 263 cm−1. [ABSTRACT FROM AUTHOR]

The structures of gas-phase group nine cation–nitrous oxide metal–ligand complexes, M+(N2O)n (M = Co, Rh, Ir; n = 2–7) have been determined by a combination of infrared photodissociation spectroscopy and density functional theory. The infrared spectra were recorded in the region of the N2O asymmetric (N=N) stretch using the inert messenger technique and show spectroscopically distinct features for N- and O-bound isomers. The evolution of the spectra with increasing ligand number is qualitatively different for each of the metal ions studied here with only Co+(N2O)n complexes behaving similarly to the coinage metal complexes studied previously. The rich variety of electronic and isomeric structures identified make these species attractive targets for infrared-driven, isomer selective intra-complex chemistry. [ABSTRACT FROM AUTHOR]

Magnetic field effect studies have been conducted on a variety of flavin-based radical pair systems chosen to model the magnetosensitivity of the photoinduced radical pairs found in cryptochrome flavoproteins. Cryptochromes are blue-light photoreceptor proteins which are thought to mediate avian magnetoreception, an hypothesis supported by recent in vitro observations of magnetic field-dependent reaction kinetics for a light-induced radical pair in a cryptochrome from the plant Arabidopsis thaliana. Many cryptochromes are difficult to express in large quantities or high concentrations and are easily photodegraded. Magnetic field effects are typically measured by spectroscopic detection of the transient radical (pair) concentrations. Due to its low sensitivity, single-pass transient absorption spectroscopy can be of limited use in such experiments and much recent work has involved development of other methodologies offering improved sensitivity. Here we explore the use of flavin fluorescence as the magnetosensitive probe and demonstrate the exceptional sensitivity of this technique which allows the detection of magnetic field effects in flavin samples at sub-nanomolar concentrations and in cryptochromes. [ABSTRACT FROM AUTHOR]

The spectroscopy and UV photodissociation dynamics of Cu2 and CuO have been studied using a combination of one- and two-colour excitation and velocity map imaging. Resonant excitation of Cu2via the J ← X 1Σg+ transition leads to significant fragmentation which is interpreted in terms of a combination of direct dissociation of Cu2+ 2Π produced in the resonant two-photon ionization process and dissociation of excited Cu2 states above the ionization threshold. By fitting of the kinetic energy release spectra obtained from the velocity map images, we determine a value for the dissociation energy of the cation of D0 (Cu2+, X 2Σg+) of 1.713 ± 0.025 eV, which, when combined with known ionization energies, yields D0 (Cu2, X 1Σg+) = 1.886 ± 0.026 eV. In other experiments, resonant two colour (1 + 1′) excitation of CuO via a range of excited states (C, D, F, H), yields unusually simple VMI images indicating fragmentation into a single dissociation channel which has been identified as Cu* 2D3/2 + O* 1D. Taken together, this data gives a CuO bond dissociation energy of 3.041 ± 0.030 eV. Finally, the production of Cu2+ with kinetic energy = 705 ± 75 cm−1 is tentatively interpreted as photolysis of Cu3 yielding Cu* + Cu2 X 1Σg+ from which a dissociation energy of Cu3 of 0.605 ± 0.030 eV is deduced. [ABSTRACT FROM AUTHOR]

We report a combined experimental and computational study of carbon dioxide activation at gas-phase Ho + and HoO + centres. Infrared action spectra of Ho(CO 2 ) n + and [HoO(CO 2 ) n ] + ion-molecule complexes have been recorded in the spectral region 1700-2400 cm -1 and assigned by comparison with simulated spectra of energetically low-lying structures determined by density functional theory. Little by way of activation is observed in Ho(CO 2 ) n + complexes with CO 2 binding end-on to the Ho + ion. By contrast, all [HoO(CO 2 ) n ] + complexes n ≥ 3 show unambiguous evidence for formation of a carbonate radical anion moiety, . The signature of this structure, a new vibrational band observed around 1840 cm -1 for n = 3, continues to red-shift monotonically with each successive CO 2 ligand binding with net charge transfer from the ligand rather than the metal centre.

Understanding the catalytic decomposition of nitrous oxide on finely divided transition metals is an important environmental issue. In this study, we present the results of a combined infrared action spectroscopy and quantum chemical investigation of molecular N2O binding to isolated Aun+ (n ≤ 7) and Con+ (n ≤ 5) clusters. Infrared multiple-photon dissociation spectra have been recorded in the regions of both the N[double bond, length as m-dash]O (1000-1400 cm-1) and N[double bond, length as m-dash]N (2100-2450 cm-1) stretching modes of nitrous oxide. In the case of Aun+ clusters only the ground electronic state plays a role, while the involvement of energetically low-lying excited states in binding to the Con+ clusters cannot be ruled out. There is a clear preference for N-binding to clusters of both metals but some O-bound isomers are observed in the case of smaller Con(N2O)+ clusters.

Infrared multiple-photon dissociation spectroscopy has been applied to study Pt n (N 2 O) + (n = 1-8) clusters which represent entrance-channel complexes on the reactive potential energy surface for nitrous oxide decomposition on platinum. Comparison of spectra recorded in the spectral region 950 cm -1 to 2400 cm -1 with those simulated for energetically low-lying structures from density functional theory shows a clear preference for molecular binding via the terminal N atom, though evidence of O-binding is observed for some cluster sizes. Enhanced reactivity of Pt n + n≥ 6 clusters towards N 2 O is reflected in the calculated reactive potential energy surfaces and, uniquely in the size range studied, Pt 6 (N 2 O) + proved impossible to form in significant number density even with cryogenic cooling of the cluster source. Infrared-driven N 2 O decomposition, resulting in the formation of cluster oxides, Pt n O + , is observed following vibrational excitation of several Pt n (N 2 O) + complexes.

The structures of gas-phase group nine cation-nitrous oxide metal-ligand complexes, M + (N 2 O) n (M = Co, Rh, Ir; n = 2-7) have been determined by a combination of infrared photodissociation spectroscopy and density functional theory. The infrared spectra were recorded in the region of the N 2 O asymmetric (N[double bond, length as m-dash]N) stretch using the inert messenger technique and show spectroscopically distinct features for N- and O-bound isomers. The evolution of the spectra with increasing ligand number is qualitatively different for each of the metal ions studied here with only Co + (N 2 O) n complexes behaving similarly to the coinage metal complexes studied previously. The rich variety of electronic and isomeric structures identified make these species attractive targets for infrared-driven, isomer selective intra-complex chemistry.

The spectroscopy and UV photodissociation dynamics of Cu2 and CuO have been studied using a combination of one- and two-colour excitation and velocity map imaging. Resonant excitation of Cu2 via the J ← X (1)Σg(+) transition leads to significant fragmentation which is interpreted in terms of a combination of direct dissociation of Cu2(+ 2)Π produced in the resonant two-photon ionization process and dissociation of excited Cu2 states above the ionization threshold. By fitting of the kinetic energy release spectra obtained from the velocity map images, we determine a value for the dissociation energy of the cation of D0 (Cu2(+), X (2)Σg(+)) of 1.713 ± 0.025 eV, which, when combined with known ionization energies, yields D0 (Cu2, X (1)Σg(+)) = 1.886 ± 0.026 eV. In other experiments, resonant two colour (1 + 1') excitation of CuO via a range of excited states (C, D, F, H), yields unusually simple VMI images indicating fragmentation into a single dissociation channel which has been identified as Cu* (2)D3/2 + O* (1)D. Taken together, this data gives a CuO bond dissociation energy of 3.041 ± 0.030 eV. Finally, the production of Cu2(+) with kinetic energy = 705 ± 75 cm(-1) is tentatively interpreted as photolysis of Cu3 yielding Cu* + Cu2 X (1)Σg(+) from which a dissociation energy of Cu3 of 0.605 ± 0.030 eV is deduced.

Broadband cavity-enhanced absorption spectroscopy has been used to record, in real time, the absorption spectrum of microlitre volume aqueous phase droplets within a microfluidic chip assembly. Using supercontinuum radiation and broadband coated external mirrors, the full visible spectrum (430 nm < λ < 700 nm) of each passing droplet is acquired in situ at high repetition rates (273 Hz/3.66 ms acquisition time) and high sensitivity (α(min) < 10(-2) cm(-1)). The possibilities for further improvements in sensitivity and acquisition rate using custom designed chips are discussed.

A white light-emitting diode (LED) with emission between 420 and 700 nm and a supercontinuum (SC) source with emission between 450 and 2500 nm have been compared for use in evanescent wave broadband cavity-enhanced absorption spectroscopy (EW-BB-CEAS). The method is calibrated using a dye with known absorbance. While the LED is more economic as an excitation source, the SC source is superior both in terms of baseline noise (noise equivalent absorbances lower than 10(-5) compared to 10(-4) absorbance units (a.u.)) and accuracy of the measurement; these baseline noise levels are comparable to evanescent wave cavity ringdown spectroscopy (EW-CRDS) studies while the accessible spectral region of EW-BB-CEAS is much larger (420-750 nm in this study, compared to several tens of nanometres for EW-CRDS). The improvements afforded by the use of an SC source in combination with a high sensitivity detector are demonstrated in the broadband detection of electrogenerated Ir(IV) complexes in a thin-layer electrochemical cell arrangement. Excellent signal to noise is achieved with 10 micros signal accumulation times at a repetition rate of 600 Hz, easily fast enough to follow, in real time, solution kinetics and interfacial processes.

The reactions of gas phase rhodium clusters, Rhn+/- (n<30), with nitrous oxide, N2O, have been investigated under single collision conditions by Fourier transform ion cyclotron resonance mass spectrometry. The only significant reaction observed is the sequential generation of oxides. Absolute rate constants for the reactions of all clusters have been determined and, in the case of the cationic clusters especially, they exhibit large fluctuations as a function of cluster size with local minima observed for n=5, 19, 28. Striking similarities are observed with the variation in rate constants for these clusters in reactions with small hydrocarbons (C. Adlhart and E. Uggerud, J. Chem. Phys., 2005, 123, 214709). Corresponding size effects are also observed but are less marked in the reactions of the anionic clusters. The reactions of several clusters exhibit marked deviations from simple pseudo-first-order kinetics suggesting the presence of multiple isomeric forms: Rh11+, Rh12+ and Rh8- exhibit characteristic biexponential decays which are interpreted in terms of the existence of different structural forms of the cluster which have markedly different reactivity. By contrast, Rh6+, Rh7+ and Rh8+ show rates which apparently increase with time, probably due to collisional activation. Thermalisation of the clusters prior to reaction by exposure to pulses of argon results in changes to the kinetics of these anomalous systems which can be explained in terms of collision induced isomerisation.

The rate of propagation in the free-radical polymerization of methyl methacrylate in an ionic liquid has been determined and shows unprecedented solvent-induced acceleration, partially explaining the surprising increase in overall rates of polymerization and molecular weights in these solvents.