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To facilitate direct spectroscopic observation of hydrogen chloride anions (HCl-), electron bombardment of CH3Cl diluted in excess Ar during matrix deposition was used to generate this anion. Subsequent characterization were performed by IR spectroscopy and quantum chemical calculations. Moreover the band intensity of HCl- decays slowly when the matrix sample is maintained in the dark for a prolonged time. High-level ab inito calculation suggested that HCl- is only weakly bound. Atom-in-molecule charge analysis indicated that both atoms of HCl- are negatively charged and the Cl atom is hypervalent. [ABSTRACT FROM AUTHOR]

Three-center two-electron bonds are important for understanding electron-deficient molecules. To examine such a molecule, we produced a diborane(5) anion with a single-bridged structure upon electron bombardment during matrix deposition of Ar containing a small proportion of diborane(6). The diborane(5) anion was destroyed upon photolysis at 180, 220, 385, and 450 nm, but not at 532 nm. Moreover, the possible formation of neutral diborane(5) was observed upon photolysis at 385 and 450 nm, whereas neutral diborane(3) was observed upon photolysis at 180 and 220 nm. The observed line wavenumbers, relative intensities, and isotopic ratios of the diborane(5) anion agreed satisfactorily with those predicted by density functional theory calculations at the B3LYP/aug-cc-pVTZ level of theory. Thus, this method produced the boron hydride anion of interest with few other fragments, which enabled us to clearly identify the IR spectrum of the diborane(5) anion. [ABSTRACT FROM AUTHOR]

Irradiation of samples of solid Ne near 3.0 K containing ethene (C2H4) with vacuum ultraviolet radiation at 120 nm from synchrotron yielded new spectral lines at 3141.0, 2953.6, 2911.5, 1357.4, 677.1, 895.3, and 857.0 cm-1. These features are assigned to α-CH stretching (ν1), CH2 antisymmetric stretching (ν2), CH2 symmetric stretching (ν3), CH2-bending (ν5), HCCH cis bending (ν7), CH2 out-of-plane bending (ν8), and α-CH out-of-plane bending (ν9) modes of C2H3, respectively, based on results of 13C- and D-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP and PW91PW91/aug-cc-pVTZ) predict vibrational wavenumbers, IR intensities, and isotopic ratios of vinyl radical that agree satisfactorily with our experimental results. [ABSTRACT FROM AUTHOR]

Following the photodissociation of o-fluorotoluene [o-C6H4(CH3)F] at 193 nm, rotationally resolved emission spectra of HF(1≤=v≥=4) in the spectral region of 2800–4000 cm-1 are detected with a step-scan Fourier transform spectrometer. HF(v≤=4) shows nearly Boltzmann-type rotational distributions corresponding to a temperature ∼1080 K; a short extrapolation from data in the period of 0.5–4.5 μs leads to a nascent rotational temperature of 1130±100 K with an average rotational energy of 9±2 kJ mol-1. The observed vibrational distribution of (v=1):(v=2):(v=3)=67.6: 23.2: 9.2 corresponds to a vibrational temperature of 5330±270 K. An average vibrational energy of 25±312 kJ mol-1 is derived based on the observed population of HF(1≤=v≤=3) and estimates of the population of HF (v=0 and 4) by extrapolation. Experiments performed on p-fluorotoluene [p-C6H4(CH3)F] yielded similar results with an average rotational energy of 9±2 kJ mol-1 and vibrational energy of 26±312 kJ mol-1 for HF. The observed distributions of internal energy of HF in both cases are consistent with that expected for four-center elimination. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF. An observed vibrational energy of HF produced from fluorotoluene slightly smaller than that from fluorobenzene might indicate the involvement of seven-membered-ring isomers upon photolysis. [ABSTRACT FROM AUTHOR]

Irradiation of an Ar matrix sample containing H[sub 2]S and CO (or OCS) with an ArF excimer laser at 193 nm yields trans-HSCO (denoted t-HSCO). New lines at 1823.3, 931.6, and 553.3 cm-1 appear after photolysis and their intensity enhances after annealing; secondary photolysis at 248 nm diminishes these lines and produces OCS and CO. These lines are assigned to C–O stretching, HSC-bending, and C–S stretching modes of t-HSCO, respectively, based on results of [sup 13]C-isotopic experiments and theoretical calculations. Theoretical calculations using density-functional theories (B3LYP and PW91PW91) predict four stable isomers of HSCO: t-HSCO, c-HSCO, HC(O)S, and c-HOCS, listed in increasing order of energy. According to calculations with B3LYP/aug-cc-pVTZ, t-HSCO is planar, with bond lengths of 1.34 Å (H–S), 1.81 Å (S–C), and 1.17 Å (C–O), and angles /_ HSC≅93.4° and /_ SCO≅128.3°; it is more stable than c-HSCO and HC(O)S by ∼9 kJ mol-1 and more stable than c-HOCS by ∼65 kJ mol-1. Calculated vibrational wave numbers, IR intensities, and [sup 13]C-isotopic shifts for t-HSCO fit satisfactorily with experimental results. This new spectral identification of t-HSCO provides information for future investigations of its roles in atmospheric chemistry. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]