Infrared Spectra of Products of the Reaction of H Atoms with O2 Trapped in Solid Neon: HO2, HO2+, HOHOH–, and H2O(HO)

Cryogenic Vibrationally Resolved Photoelectron Spectroscopy of OH-(H2O): Confirmation of Multidimensional Franck-Condon Simulation Results for the Transition State of the OH + H2O Reaction

We present a transition state spectroscopic study of the OH + H₂O reaction using the experimental technique of cryogenic negative ion photoelectron spectroscopy (NIPES). The recorded NIPE spectrum at 193 nm exhibits multiple vibrational progressions that include excitations to the shared H atom antisymmetric stretching mode with an interval of 0.32 eV as well as other progressions, mainly involving the H bending and O···O symmetric stretching modes. The vertical detachment energy (VDE) was measured at 3.53 eV, whereas an upper limit for the adiabatic detachment energy (ADE) was estimated at 2.90 eV. These values are in excellent agreement with the theoretically computed values of 3.51 and 2.87 eV, respectively, obtained at the CCSD(T)/aug-cc-pV5Z level of theory. The recorded NIPE spectrum is in very good agreement when compared to the one recently reported from four-dimensional Franck-Condon simulations, in which a similar spectral profile was predicted. Besides observing the ground state, we identified a charge-transfer excited state in the form of [OH^-(H₂O)⁺] with a relative energy of 1.39 eV, well matching the previous prediction of 1.36 eV.

Threshold photoelectron spectroscopy of the HO2 radical

We report a synchrotron radiation vacuum ultraviolet photoionization study of the hydroperoxyl radical (HO₂), a key reaction intermediate in combustion and atmospheric chemistry as well as astrochemistry, using double imaging photoelectron photoion coincidence spectroscopy. The HO₂ radical is formed in a microwave discharge flow tube reactor through a set of reactions initiated by F atoms in a CH₄/O₂/He gas mixture. The high-resolution threshold photoelectron spectrum of HO₂ in the 11 eV-12 eV energy range is acquired without interferences from other species and assigned with the aid of theoretically calculated adiabatic ionization energies (AIEs) and Franck-Condon factors. The three vibrational modes of the radical cation HO₂ ⁺, the H-O stretch, the H-O-O bend, and the O-O stretch, have been identified, and their individual frequencies are measured. In addition, the AIEs of the X³A″ ground state and the a¹A' first excited electronic state of HO₂ ⁺ are experimentally determined at 11.359 ± 0.003 eV and 11.639 ± 0.005 eV, respectively, in agreement with high-level theoretically computed results. Furthermore, the former AIE value provides validation of thermochemical networks used to extract the enthalpy of formation of the HO₂ radical.

Global Potential Energy Surface for HO2+ Using the CHIPR Method

An analytical potential energy function for the title ion based on the combined hyperbolic inverse power representation (CHIPR) method and its characteristics are discussed at length in the present work. The curves of two diatomic ions, O₂⁺ and OH⁺, are also obtained within the same approach. The model PES so obtained exhibits extraordinary flexibility in describing with subchemical accuracy even the weak topological features near the higher energy regions. Thus, structural properties predicted by the model may help spectroscopists who want to compare their experimental values with the ones from theory. The relaxed PESs in various coordinates have been calculated by relaxing the O₂ bond distance using the present model, thus throwing light on all the possible isomers and their interconversions. The latest estimates of IR frequencies for three vibrational modes have been compared with the computed frequencies using the present model, and the agreement seems encouraging.

First multi-tool exploration of a gas-condensate-pyrolysate system from the environment of burning coal mine heaps: An in situ FTIR and laboratory GC and PXRD study based on Upper Silesian materials

A methodological approach to the complex geochemical analysis of the coal fire in burning coal mine heaps (BCMH) of Upper Silesian Coal Basin has been developed. The other approach used is gas chromatography and indicatory tubes. Powder X-Ray Diffraction is applied for phase analysis to determine the species composition of mineral condensates present within and around gas flues. The gas compositions are proved to be extremely variable, when comparing both different BCMH and flues or flue zones of the same heaps. One outstanding determination concerns GeCl₄, found in most samples often in large quantities. No evident dependence between the gas and mineral condensate compositions is found: N-rich condensates may but do not have to be associated with NH₃-, pyridine-, or NO_x-rich gases. This is also true for S-rich and Cl-rich mineralization in connection with gases of SO₂, H₂S, OCS, CS₂, thiophene, dimethyl sulfide, dimethyl disulfide, HCl, and various halogenated hydrocarbons. Fluorine is rarely present as HF, whereas SiF₄ occurs more frequently and in much larger quantities. AsH₃ is mainly a trace gas but may locally be enriched. Besides the common gases, a number of trace gases is also determined based on residual FTIR spectra. Those with the highest presence chance include cyanogen isocyanate, cyanogen N-oxide, (iso)cyanic acid, c-cyanomethanimine (ethylenediimine), isocyanatomethane, iodocyanoacetylene, acetonitrile, acetaldehyde, m-hydroxybenzonitrile (m-cyanophenol), isonitrosyl chloride, nitrosyl isocyanide, difluorosilane, pentacene, triphenylene, thiazolidine, cyclohexane, and a trinitrenetriazine. The occurrence of some metals and semimetals (e.g., Al, Mg, Ga) as neutral hydroxides, suggested by other authors to occur in natural gases, is possibly confirmed. The presence of trace metal carbonyls, nitrosyls and hydrides is also possible.

High-resolution infrared spectroscopy of O2H+ in a cryogenic ion trap

The protonated oxygen molecule, O₂H⁺, and its helium complex, He-O₂H⁺, have been investigated by vibrational action spectroscopy in a cryogenic 22-pole ion trap. For the He-O₂H⁺ complex, the frequencies of three vibrational bands have been determined by predissociation spectroscopy. The elusive O₂H⁺ has been characterized for the first time by high-resolution rovibrational spectroscopy via its ν₁ OH-stretching band. Thirty-eight rovibrational fine structure transitions with partly resolved hyperfine satellites were measured (56 resolved lines in total). Spectroscopic parameters were determined by fitting the observed lines with an effective Hamiltonian for an asymmetric rotor in a triplet electronic ground state, X̃³A^'', yielding a band origin at 3016.73 cm^-1. Based on these spectroscopic parameters, the rotational spectrum is predicted, but not yet detected.

Quasi-classical trajectory studies on the full-dimensional accurate potential energy surface for the OH + H2O = H2O + OH reaction

The first accurate PES for the OH + H₂O reaction is developed by using the permutation invariant polynomial-neural network method to fit ∼48 000 CCSD(T)-F12a/AVTZ calculated points.

An Evaluation of Gas Phase Enthalpies of Formation for Hydrogen-Oxygen (HxOy) Species

We have compiled gas phase enthalpies of formation for nine hydrogen-oxygen species (HxOy) and selected recommended values for H, O, OH, H2O, HO2, H2O2, O3, HO3, and H2O3. The compilation consists of values derived from experimental measurements, quantum chemical calculations, and prior evaluations. This work updates the recommended values in the NIST-JANAF (1985) and Gurvich et al. (1989) thermochemical tables for seven species. For two species, HO3 and H2O3 (important in atmospheric chemistry) and not found in prior thermochemical evaluations, we also provide supplementary data consisting of molecular geometries, vibrational frequencies, and torsional potentials which can be used to compute thermochemical functions. For all species, we also provide supplementary data consisting of zero point energies, vibrational frequencies, and ion reaction energetics.

I + (H2O)2 → HI + (H2O)OH Forward and Reverse Reactions. CCSD(T) Studies Including Spin-Orbit Coupling

The potential energy profile for the atomic iodine plus water dimer reaction I + (H2O)2 → HI + (H2O)OH has been explored using the "Gold Standard" CCSD(T) method with quadruple-ζ correlation-consistent basis sets. The corresponding information for the reverse reaction HI + (H2O)OH → I + (H2O)2 is also derived. Both zero-point vibrational energies (ZPVEs) and spin-orbit (SO) coupling are considered, and these notably alter the classical energetics. On the basis of the CCSD(T)/cc-pVQZ-PP results, including ZPVE and SO coupling, the forward reaction is found to be endothermic by 47.4 kcal/mol, implying a significant exothermicity for the reverse reaction. The entrance complex I···(H2O)2 is bound by 1.8 kcal/mol, and this dissociation energy is significantly affected by SO coupling. The reaction barrier lies 45.1 kcal/mol higher than the reactants. The exit complex HI···(H2O)OH is bound by 3.0 kcal/mol relative to the asymptotic limit. At every level of theory, the reverse reaction HI + (H2O)OH → I + (H2O)2 proceeds without a barrier. Compared with the analogous water monomer reaction I + H2O → HI + OH, the additional water molecule reduces the relative energies of the entrance stationary point, transition state, and exit complex by 3-5 kcal/mol. The I + (H2O)2 reaction is related to the valence isoelectronic bromine and chlorine reactions but is distinctly different from the F + (H2O)2 system.

Cold condensation of dust in the ISM

The condensation of complex silicates with pyroxene and olivine composition under conditions prevailing in molecular clouds has been experimentally studied. For this purpose, molecular species comprising refractory elements were forced to accrete on cold substrates representing the cold surfaces of surviving dust grains in the interstellar medium. The efficient formation of amorphous and homogeneous magnesium iron silicates at temperatures of about 12 K has been monitored by IR spectroscopy. The gaseous precursors of such condensation processes in the interstellar medium are formed by erosion of dust grains in supernova shock waves. In the laboratory, we have evaporated glassy silicate dust analogs and embedded the released species in neon ice matrices that have been studied spectroscopically to identify the molecular precursors of the condensing solid silicates. A sound coincidence between the 10 microm band of the interstellar silicates and the 10 microm band of the low-temperature siliceous condensates can be noted.

The exothermic HCl + OH·(H2O) reaction: removal of the HCl + OH barrier by a single water molecule

The entrance complex, transition state, and exit complex for the title reaction have been investigated using the CCSD(T) method with correlation consistent basis sets up to cc-pVQZ. The stationary point geometries for the reaction are related to but different from those for the water monomer reaction HCl + OH → Cl + H2O. Our most important conclusion is that the hydrogen-bonded water molecule removes the classical barrier entirely. For the endothermic reverse reaction Cl + (H2O)2, the second water molecule lowers the relative energies of the entrance complex, transition state, and exit complex by about 4 kcal/mol. The title reaction is exothermic by 17.7 kcal/mol. The entrance complex HCl⋯OH·(H2O) is bound by 6.9 kcal/mol relative to the separated reactants. The classical barrier height for the reverse reaction is predicted to be 16.5 kcal/mol. The exit complex Cl⋯(H2O)2 is found to lie 6.8 kcal/mol below the separated products. The potential energy surface for the Cl + (H2O)2 reaction is radically different from that for the valence isoelectronic F + (H2O)2 system.