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A photochemical study of water (H2 16O, H2 18O, D2 16O, and D2 18O) in solid Xe is described. The water–Xe samples were irradiated at 193 nm and then annealed at 40–50 K, which led to formation of various isotopomers of Xe-containing molecules, HXeOH and HXeH. This diffusion-controlled formation of HXeH and HXeOH consumes the main part of hydrogen atoms generated in the matrix during photolysis. Both photodecomposition profiles and ultraviolet (UV) absorption spectra of HXeOH and HXeH feature a broad absorption band of these species around 240 nm corresponding to the transition to the repulsive excited states. It is also found that HXeOH and HXeH molecules can be thermally destroyed in similar time scales of ∼10 min at about 54 and 66 K, respectively. This clear difference between the decomposition temperatures for HXeOH and HXeH suggests the intrinsic basis of the decomposition process, which possibly occurs over the barriers of the bending coordinates. The absence of strong H–D isotope effect in this thermal decomposition indicates that tunneling of hydrogen is not essentially involved in the process at these temperatures. However, the local disorder of a Xe matrix seems to produce inhomogeneous broadening of the activation energies of the decomposition as indicated by the observed nonexponential decay kinetics. Upon photolysis and annealing of the H2O–Xe samples, monomeric and complexed hydrogen peroxide is formed originating, at least partially, from water clusters stabilized in solid Xe. In addition, we report the vibrational data on various isotopomers of HXeH, HXeOH, H2O, OH, and OH⋯H2O isolated in solid Xe.

The high overtone‐induced isomerization of glycolic acid in a low‐temperature argon matrix was investigated using Raman spectroscopy. The Raman spectrum of glycolic acid is presented, and the spectral assignment is supported by vibrational anharmonic calculations. The high overtone excitation of the lowest energy conformer (SSC) at 532 nm induced direct conformational isomerization to higher energy conformers (GAC and AAT). Furthermore, upon excitation at 532 nm GAC and AAT isomerized back to SSC and photo‐induced equilibrium was observed between the conformers. Kinetic model was used to describe the observed isomerization and isomerization rate constants were obtained. No experimental evidence of isomerization between GAC and AAT nor other higher energy conformers were observed.

High-overtone induced chemistry of oxalic acid (OA) isolated in a low-temperature argon matrix was investigated using Raman spectroscopy. The Raman spectra of three conformers of OA are presented and discussed. Upon excitation of high overtone combination bands by 532 nm irradiation of the lowest energy cTc structure, the isomerization and unimolecular decomposition of OA were observed. Dissociation was induced presumably by absorption into the 5A(g) + B(u) vibrational state of the OH stretching mode of cTc. The photodecomposition leads to the formation of CO, CO(2), and H(2)O products. The experimental observations were supported by computational studies and vibrational anharmonic calculations.

Articles you may be interested inSystematic theoretical studies of the interaction of 1,4-diazabicyclo [2.2.2]octane (DABCO) with rare gases A combining rule calculation of the ground state van der Waals potentials of the mercury rare-gas complexes Global minima for rare gas clusters containing one alkali metal ion Accurate relativistic many-body calculations of van der Waals coefficients C 8 and C 10 for alkali-metal dimers Ab initio and molecular-dynamics studies on rare gas hydrides: Potential-energy curves, isotropic hyperfine properties, and matrix cage trapping of atomic hydrogenThe rare gas ͑Ne, Ar, Kr, Xe͒-alkali metal ͑Li, Na͒ ground-state pair interaction potentials and distance-dependent isotropic hyperfine coupling constants are evaluated by coupled-cluster approaches at the van der Waals region of the dimers. The computed properties are further utilized in classical molecular dynamics simulations of rare gas lattices doped with alkali atoms. Atomic trajectories and time averaged hyperfine constants are obtained from the simulations and exploited to provide theoretical insights into experimentally observed atomic trapping and dynamics of alkali metal atoms in rare gas matrices. The simulations support our previous electron paramagnetic resonance ͑EPR͒ data ͓Chem. Phys. Lett, 310, 245 ͑1999͔͒, suggesting that alkali metal atoms, while generated by laser vaporization, do trap in single substitutional sites, whereas thermal atom sources yield trapping in multiple substitutional sites. In order to theoretically reproduce the EPR spectra for the latter case, more than six neighboring vacancies had to be included in the model system. Based on the simulations, the trapped atoms are able to move rather freely within the extended cage.

Acetic acid (AA) monomer and its dimers were studied by means of Raman spectroscopy combined with the matrix isolation technique. All fundamental bands of CH 3 COOH monomer were identified, including the CH 3 torsional mode. Additionally, three overtone or combination modes were observed as a result of their enhanced intensities by Fermi resonance (FR). Twenty bands of the cyclic dimer (C 2h ) were identified and assigned, among which appear all intermolecular modes. Bands due to two different higher energy forms of the dimer were also identified. The experimental assignments are supported by ab initio calculations.

The electronic UV absorption spectra of thermal reaction products H−Xe−Y (Y= Cl, Br, I, or CN) have been measured in solid Xe at 12 K. The spectra are obtained after the annealing of an extensively irradiated matrix doped with an HCl, HBr, HI, or HCN precursor. The spectral assignment is based on the correlation between the UV spectra and the known infrared absorptions of these compounds. An analysis of the annealing behavior of the UV absorptions due to H−Xe−Y, Y/Xe and H/Xe yields a quantitative estimate that 20−30% of the photogenerated Y is converted to H−Xe−Y. Present multireference configuration interaction (MRCI) calculations provide strong support that the spectral observations are due to the A 1Σ ← X 1Σ transitions of H−Xe−Y. The spectral width of the absorptions indicate that the transitions are from a bound ground state to a repulsive excited state.

Raman spectroscopy combined with the matrix isolation technique was employed to study the 193-nm photodecomposition products of formic acid in an argon matrix. The Raman-active fundamentals belonging to the CO(2) + H(2) and CO + H(2)O photoproducts were assigned. Also, bands due to Fermi resonance between the stretching vibration (nu(1)) and the overtone of the bending mode (2nu(2)) of CO(2) were identified. Both ortho- and para-H(2) molecules were identified from their rotational lines S(0)(1) and S(0)(0), respectively. These bands appeared upon matrix annealing as well as after prolonged photolysis. Additionally, photolysis of FA dimers produces oxalic acid and its secondary photoproducts, CO(2) + CO + H(2)O. All experimental studies were supported by ab initio calculations.