Photolysis of HNCO at wavelengths between 266 and 193 nm is studied in solid Xe with FTIR and laserinduced fluorescence methods. The channels HNCO f H + NCO (a) and HNCO f NH + CO (b) are operative in a Xe matrix. Channel b produces both isolated fragments and NH‚‚‚CO complexes as characterized by the CO absorption. The MP2/6-311++G(3df,3pd) calculations are presented for the NH-CO complexes and compared with the experimental data. Photolysis of NCO produces mainly NO + C. A part of the carbon atoms form C 2 after which C 2 -is created in a photoinduced charge transfer reaction. For comparison, in solid Kr, photolysis of HNCO produces additionally HOCN but this channel is absent in a Xe matrix. Upon annealing of the partially photolyzed matrix at 50 K, hydrogen atoms are mobilized and a radical H 2 NCO is formed by a reaction of a hydrogen atom with a HNCO molecule. Four IR absorptions of H 2 NCO are observed and they agree well with the MP2/6-311++G(3df,3pd) calculations. The assignment is supported by experiments with DNCO. The threshold for the photodecomposition of H 2 NCO is between 365 and 405 nm.

UV photolysis of hydrogen peroxide (H2O2) in various rare-gas matrixes is comparatively studied. The photorecovery of H2O2 from the tight H2O⋯O complex is observed in Kr and Xe matrixes, in addition to this reaction in an Ar matrix found previously. The similarity of spectral position and efficiency of the photorecovery reaction in various rare-gas solids indicates its fundamental character, supports charge-transfer excitation of H2O⋯O as its origin, and preserves promises to find this photoreaction in media of environmental importance. In UV photolysis of H2O2, the relatively small concentration of isolated OH radicals is found in a Kr matrix, and no OH radicals appear in a Xe matrix, and this trend is discussed in terms of delayed cage exit. Moreover, additional species photogenerated from H2O2 in a Xe matrix as well as the absence of OH radicals might be connected with participation of some hidden intermediates (HOXeOH, HXeOOH, etc.) in the dynamics, thus, catalyzing new photodissociation channels. Among the photolysis products, the loose H2O//O complex is suggested to be stabilized in Kr and Xe matrixes. This loosely bound complex is quasistable and decomposes at relatively low temperatures (below 20 K) quantitatively forming the known tight H2O⋯O structure. This low-temperature process offers one additional example of short-range atomic mobility introduced recently in the literature.

The preparation and characterization of a novel rare-gas-containing compound HXeNCO in solid Xe is described. HXeNCO is formed in two ways. Photolysis of HNCO at 193 nm in solid Xe directly produces HXeNCO providing the first experimental evidence of direct photoinduced formation of a HXY-type rare-gas compound (X = Xe, Kr; Y is an electronegative fragment), which can be attributed to relatively high photostability of HXeNCO. This finding particularly shows that the HXY compounds can be intermediates in the photolysis of HY in the presence of X. The amount of HXeNCO produced initially in photolysis of HNCO remains small because HXeNCO decomposes under irradiation. More efficient production of HXeNCO is achieved in the thermal reaction H + Xe + NCO → HXeNCO after photolysis of HNCO. HXeNCO has two strong IR absorptions:  the asymmetric NCO stretch at 2148.3 cm-1 and the Xe−H stretch at 1788.1 cm-1. The assignment is supported by the deuteration experiments and the ab initio calculations. HXeNCO decomposes at 405 nm irradiation producing HNCO and (H + NCO).

The structure, energetics, and infrared spectrum of the H2O2-CO complex have been studied computationally with the use of ab initio calculations and experimentally by FTIR matrix isolation techniques. Computations predict two stable conformations for the H2O2-CO complex, both of which show almost linear hydrogen bonds between the subunits. The carbon-attached HOOH-CO complex is the lower-energy form, and it has an interaction energy of -9.0 kJmol(-1) at the CCSD(T)/6-311++G(3df,3pd)// MP2/6-311++G(3df,3pd) level. The higher-energy form, HOOH-OC, has an interaction energy of 4.7 kJmol(-1) at the same level of theory. Experimentally, only the lower-energy form, HOOH-CO, was observed in Ar, Kr, and Xe matrices, and the hydrogen bonding results in substantial perturbations of the observed vibrational modes of both complex subunits. UV photolysis of the complex species primarily produces a complex between water and carbon dioxide, but minor amounts of HCO and trans-HOCO were found as well.

Ab initio and molecular-dynamics studies on rare gas hydrides: Potential-energy curves, isotropic hyperfine properties, and matrix cage trapping of atomic hydrogenThe trapping sites of HArF and HKrF in crystalline Ar and Kr are investigated computationally. Ab initio calculations are used to evaluate interactions between the rare gas containing molecule and a single rare gas atom. Molecular mechanics and molecular dynamics are used to study the properties of HArF and HKrF in rare gas crystals. Three different trapping configurations have been found for both molecules. The lowest-energy site is a double-substitutional ͑DS͒ configuration and the second lowest energy site is a single-substitutional ͑SS͒ one. The DS site can be interpreted to involve a 1:1 Rg¯HRgF complex ͑RgϭAr, Kr͒. The energy difference between these sites is 10.4 and 9.8 kJ/mol for HArF and HKrF, respectively. All the computational evidence shows that the experimentally observed stable site of HArF ͓J. Am. Chem. Soc. 123, 8610 ͑2001͔͒ corresponds to a DS site and the unstable site corresponds to a SS site. Relaxation of the SS site to the DS site involves the motion of a vacancy in the lattice and this suggests that HArF and HKrF can be used to study the dynamics of vacancy motion in rare gas solids.