On photochemistry of water in solid Xe: Thermal and light-induced decomposition of HXeOH and HXeH and formation of H2O2

Terahertz and mid-infrared spectroscopy of matrix-isolated clusters and matrix-sublimation ice of D2O

We have established an apparatus for terahertz and mid-infrared spectroscopy in an ultrahigh vacuum and have measured absorption spectra of D₂O clusters trapped in solid Ar. To assign terahertz absorption peaks due to the D₂O dimer, trimer, and tetramer, the dependence of the spectrum on the annealing temperature and D₂O dilution was analyzed. The assignment was also examined by ab initio calculations with the use of the "our own N-layered integrated molecular orbital and molecular mechanics" method, where the flexibility of surrounding Ar atoms was systematically incorporated. We identified all the intermolecular fundamentals of the dimer and those with significant intensities of the trimer and tetramer, whose structural symmetries were revealed to be broken down. After isolating the D₂O clusters in solid Ar, we sublimated only Ar atoms to leave behind matrix-sublimation ice, which was found to be amorphous- or crystal-like depending on the formation conditions: the dilution and sublimation temperature. The crystallinity of matrix-sublimation ice was determined by decomposing its terahertz spectrum into the spectra of amorphous and crystalline ices. Since the crystallinity got higher by raising the dilution and sublimation temperature, the diffusion of the D₂O monomer on the surface of sublimating solid Ar was found to be crucial to the crystallization of the sublimation ice.

Intriguing structural, bonding and reactivity features in some beryllium containing complexes

We highlighted our contributions to Be chemistry which include bond-stretch isomerism in Be₃²⁻ species, Be complexes bound with noble gas, CO, and N₂, Be based nanorotors, and intriguing bonding situations in some Be complexes.

Noble gas bound beryllium chromate and beryllium hydrogen phosphate: a comparison with noble gas bound beryllium oxide

Two new beryllium based compounds, beryllium hydrogen phosphate and beryllium chromate are found to have remarkable noble gas binding ability, particularly for Ar–Rn atoms.

Noble gas supported B3+ cluster: formation of strong covalent noble gas–boron bonds

Ar to Rn atoms formed exceptionally strong bonds with B₃⁺, where the Ng (HOMO) → B₃Ng₂⁺ (LUMO) σ-donation is the key term to stabilize the complexes.

Quantum chemical study on HKrC₅N, HXeC₅N, and related rare gas compounds

The recent identification of HRgC5N (Rg = Kr, Xe) in a cryogenic matrix calls for an in-depth theoretical study on these compounds. Here we present the results of CCSD(T), MP2, and DFT calculations concerning the molecular structure, stability, and vibrational spectroscopy. The procedure combining CCSD(T) calculations for variable H-Rg distances with the anharmonic description of the corresponding stretching vibration, based on a Morse-type potential energy function, was proposed and has led to good agreement between computational and experimental values for H-Rg stretching frequencies, at relatively low computational costs. High Raman scattering activity of HRgC5N and of its isomers, predicted at the DFT level, gives some prospects for the detection of these molecules with a method alternative to the IR absorption spectroscopy.

Metastable behavior of noble gas inserted tin and lead fluorides

The metastable FNgEF and FNgEF₃ (E = Sn, Pb; Ng = Kr–Rn) are the first reported neutral compounds possessing Ng–Sn and Ng–Pb covalent bonds.

On the stability of noble gas bound 1-tris(pyrazolyl)borate beryllium and magnesium complexes

1-Tris(pyrazolyl)borate beryllium and magnesium cationic complexes are found to bind Ar–Rn atoms quite effectively.

Photolabile xenon hydrides: a case study of HXeSH and HXeH

The photo-induced transformations of HXeSH and HXeH under the action of IR and visible light have been studied using FTIR spectroscopy. The xenon hydrides were produced by the X-ray induced decomposition of H2S and its isotopomers in a solid xenon matrix at 7.5 K followed by thermal annealing at the temperatures up to 45 K. Selective IR-induced photodissociation of HXeSH at 3500-2500 cm(-1) was attributed to vibrational excitation of the 3ν(H-Xe) mode. The IR-photodecomposed HXeSH molecules can be almost quantitative recovered below 22 K with very small effective activation energy (~20 meV) indicating local character of this process. Analysis of the photoactivity of xenon hydrides in the visible region revealed previously unknown absorptions for HXeSH (in the region of 400-700 nm) and HXeH (above 700 nm). The decomposition of HXeH occurs due to both direct photolysis and reactions of "hot" H atoms produced from the photodissociation of HXeSH. The efficiency of thermal recovery for both xenon hydrides after photolysis with visible light was found to be dependent on the excitation wavelength, which was explained by the effect of photon energy on spatial distribution of the dissociation fragments.

A theoretical study of stabilities, reactivities and bonding properties of XKrOH (X = F, Cl, Br and I) as potential new krypton compounds using coupled cluster, MP2 and DFT calculations

DFT andAb initiocalculations were employed to disclose the conceivable existence of new noble gas molecules, XKrOH.

A combined matrix isolation spectroscopy and cryosolid positron moderation apparatus

We describe the design, construction, and operation of a novel apparatus for investigating efficiency improvements in thin-film cryogenic solid positron moderators. We report results from solid neon, argon, krypton, and xenon positron moderators which illustrate the capabilities and limitations of our apparatus. We integrate a matrix isolation spectroscopy diagnostic within a reflection-geometry positron moderation system. We report the optical thickness, impurity content, and impurity trapping site structures within our moderators determined from infrared absorption spectra. We use a retarding potential analyzer to modulate the flow of slow positrons, and report positron currents vs. retarding potential for the different moderators. We identify vacuum ultraviolet emissions from irradiated Ne moderators as the source of spurious signals in our channel electron multiplier slow positron detection channel. Our design is also unusual in that it employs a sealed radioactive Na-22 positron source which can be translated relative to, and isolated from, the cryogenic moderator deposition substrate. This allows us to separate the influences on moderator efficiency of surface contamination by residual gases from those of accumulated radiation damage.

Insertion of noble gas atoms into cyanoacetylene: an ab initio and matrix isolation study

A computational and experimental matrix isolation study of insertion of noble gas atoms into cyanoacetylene (HCCCN) is presented. Twelve novel noble gas insertion compounds are found to be kinetically stable at the MP2 level of theory, including four molecules with argon. The first group of the computationally studied molecules belongs to noble gas hydrides (HNgCCCN and HNgCCNC), and we found their stability for Ng = Ar, Kr, and Xe. The HNgCCCN compounds with Kr and Xe have similar stability to that of previously reported HKrCN and HXeCN. The HArCCCN molecule seems to have a weaker H-Ar bond than in the previously identified HArF molecule. The HNgCCNC molecules are less stable than the HNgCCCN isomers for all noble gas atoms. The second group of the computational insertion compounds, HCCNgCN and HCCNgNC, are of a different type, and they also are kinetically stable for Ng = Ar, Kr, and Xe. Our photolysis and annealing experiments with low-temperature cyanoacetylene/Ng (Ng = Ar, Kr, and Xe) matrixes evidence the formation of two noble gas hydrides for Ng = Kr and Xe, with the strongest IR absorption bands at 1492.1 and 1624.5 cm(-1), and two additional absorption modes for each species are found. The computational spectra of HKrCCCN and HXeCCCN fit most closely the experimental data, which is the basis for our assignment. The obtained species absorb at quite similar frequencies as the known HKrCN and HXeCN molecules, which is in agreement with the theoretical predictions. No strong candidates for an Ar compound are observed in the IR absorption spectra. As an important side product of this work, the data obtained in long-term decay of KrHKr+ cations suggest a tentative assignment for the CCCN radical.

UV Photolysis Products of Propiolic Acid in Noble-Gas Solids

Photolysis (193 nm) of propiolic acid (HCCCOOH) was studied with Fourier transform infrared spectroscopy in noble-gas (Ar, Kr, and Xe) solid matrixes. The photolysis products were assigned using ab initio quantum chemistry calculations. The novel higher-energy conformer of propiolic acid was efficiently formed upon UV irradiation, and it decayed back to the ground-state conformer on a time scale of approximately 10 min by tunneling of the hydrogen atom through the torsional energy barrier. In addition, the photolysis produced a number of matrix-isolated 1:1 molecular complexes such as HCCH...CO2, HCCOH...CO, and H2O...C3O. The HCCH...CO2 complex dominated among the photolysis products, and the computations suggested a parallel geometry of this complex characterized by an interaction energy of -9.6 kJ/mol. The HCCOH...CO complex also formed efficiently, but its concentration was strongly limited by its light-induced decomposition. In this complex, the most probable geometry was found to feature the interaction of carbon monoxide with the OH group via the carbon atom, and the computational interaction energy was determined to be -18.3 kJ/mol. The formation of the strong H2O...C3O complex (interaction energy -21 kJ/mol) was less efficient, which might be due to the inefficiency of the involved radical reaction.

Infrared spectra of water clusters in krypton and xenon matrices

The infrared absorption spectra of the water molecules and small water clusters, (H(2)O)(n) with n = 2-6, trapped in solid argon, krypton, and xenon matrices have been investigated. The infrared bands of the water clusters with n = 5 and 6 in krypton and n = 3, 4, 5, and 6 in xenon matrices have been identified for the first time in the bonded OH stretching region. The frequency shifts in the bonded OH stretching band of the water dimer and trimer in xenon matrices show fairly large deviations to the red from the empirical correlation between the matrix shifts and the square root of the critical temperatures of the matrix material. The observed anomalous shifts suggest that the water dimer and trimer in solid xenon are trapped in multiple sites, and that the structures of the preferential trapping sites are different from those in argon and krypton matrices.

Chemical Compounds Formed from Diacetylene and Rare-Gas Atoms: HKrC4H and HXeC4H

New organic rare-gas compounds, HRgC4H (Rg = Kr or Xe), are identified in matrix-isolation experiments supported by ab initio calculations. These compounds are the largest molecules among the known rare-gas hydrides. They are prepared in low-temperature rare-gas matrixes via UV photolysis of diacetylene and subsequent thermal mobilization of H atoms at approximately 30 and 45 K for Kr and Xe, respectively. The strongest IR absorption bands of the HRgC4H molecules are the H-Rg stretches with the most intense components at 1290 cm(-1) for HKrC4H and at 1532 cm(-1) for HXeC4H, and a number of weaker absorptions (C-H stretching, C-C-C bending, and C-C-H bending modes) are also found in agreement with the theoretical predictions. As probably the most important result, the IR absorption spectra indicate some further stabilization of the HRgC4H molecules as compared with the corresponding HRgC2H species identified recently (Khriachtchev et al. J. Am. Chem. Soc. 2003, 125, 4696 and Khriachtchev et al. J. Am. Chem. Soc. 2003, 125, 6876). The computational energetic results support this trend. HXeC4H is predicted to be 2.5 eV lower in energy than H + Xe + C4H, which is approximately 1 eV larger than the corresponding value for HXeC2H. We expect that the larger molecules HRgC6H and HRgC8H are even more stable and the HRgC2nH species are good candidates for bulk organic rare-gas material.

Intermolecular complexes of HXeOH with water: stabilization and destabilization effects

Theoretical and matrix-isolation studies of intermolecular complexes of HXeOH with water molecules are presented. The structures and possible decomposition routes of the HXeOH-(H(2)O)(n)(n = 0, 1, 2, 3) complexes are analyzed theoretically. It is concluded that the decay of these metastable species may proceed through the bent transition states (TSs), leading to the global minima on the respective potential energy surfaces, Xe + (H(2)O)(n+1). The respective barrier heights are 39.6, 26.6, 11.2, and 0.4 kcal/mol for n = 0, 1, 2, and 3. HXeOH in larger water clusters is computationally unstable with respect to the bending coordinate, representing the destabilization effect. Another decomposition channel of HXeOH-(H(2)O)(n), via a linear TS, leads to a direct break of the H-Xe bond of HXeOH. In this case, the attached water molecules stabilize HXeOH by strengthening the H-Xe bond. Due to the stabilization, a large blue shift of the H-Xe stretching mode upon complexation of HXeOH with water molecules is featured in calculations. On the basis of this computational result, the IR absorption bands at 1681 and 1742 cm(-1) observed after UV photolysis and annealing of multimeric H(2)O/Xe matrixes are assigned to the HXeOH-H(2)O and HXeOH-(H(2)O)(2) complexes. These bands are blue-shifted by 103 and 164 cm(-1) from the known monomeric HXeOH absorption.