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We have calculated electronic transitions for sulfuric acid in the ultraviolet region using a hierarchy of coupled cluster response functions and correlation consistent basis sets. Our calculations indicate that the lowest energy singlet transition occurs at 8.42 eV with an oscillator strength of 0.01. The lowest energy triplet state occurs at 8.24 eV. Thus, the cross section of sulfuric acid in the actinic region is likely to be very small and smaller than the upper limit put on this cross section by previous experimental investigations. We estimate the cross section of sulfuric acid in the atmospherically relevant Lyman-α region (∼10.2 eV) to be ∼6 × 10 −17cm 2molecule −1, a value approximately 30 times larger than the speculative value used in previous atmospheric simulations. We have calculated the Jvalues for photodissociation of sulfuric acid with absorption of visible, UV, and Lyman-α radiation, at altitudes between 30 and 100 km. We find that the dominant photodissociation mechanism of sulfuric acid below 70 km is absorption in the visible region by OH stretching overtone transitions, whereas above 70 km, absorption of Lyman-α radiation by high energy Rydberg excited states is the favored mechanism. The low lying electronic transitions of sulfuric acid in the UV region do not contribute significantly to its dissociation at any altitude. [ABSTRACT FROM AUTHOR]

We have calculated frequencies and intensities of fundamental and overtone vibrational transitions in water and water dimer with use of different vibrational methods. We have compared results obtained with correlation-corrected vibrational self-consistent-field theory and vibrational second-order perturbation theory both using normal modes and finally with a harmonically coupled anharmonic oscillator local mode model including OH-stretching and HOH-bending local modes. The coupled cluster with singles, doubles, and perturbative triples ab initio method with augmented correlation-consistent triple- Dunning and atomic natural orbital basis sets has been used to obtain the necessary potential energy and dipole moment surfaces. We identify the strengths and weaknesses of these different vibrational approaches and compare our results to the available experimental results. [ABSTRACT FROM AUTHOR]

We have calculated the stationary points and internal reaction coordinate pathway for the dissociation of fluorosulfonic acid (FSO3H) and chlorosulfonic acid (ClSO3H). These sulfonic acids dissociate to sulfur trioxide and hydrogen fluoride and chloride, respectively. We have calculated the frequencies and intensities of the OH-stretching transitions of FSO3H and ClSO3H with an anharmonic oscillator local mode model. We find that excitation of the fourth and third OH-stretching overtones provide adequate energy for photodissociation of FSO3H and ClSO3H, respectively. We propose that experimental detection of the products of OH-stretching overtone-induced photodissociation of FSO3H and ClSO3H would be easier than the sulfuric acid (H2SO4) equivalent. The photodissociation of H2SO4is thought to be important in the stratosphere. The FSO3H and ClSO3H experiment could be used in proxy to support the recently proposed OH-stretching overtone-induced photodissociation mechanism of H2SO4. [ABSTRACT FROM AUTHOR]

Vapor-phase OH-stretching overtone spectra of methanesulfonic acid and trifluoromethanesulfonic acid were recorded in the vOH4 and 5 regions using cavity ring-down spectroscopy. We compare these spectra to those of sulfuric acid to consider the effect on vibrational overtone spectra of replacing one of the OH groups with a more or less electronegative group. We complement our experimental work with anharmonic oscillator local mode calculations of the OH-stretching frequencies and intensities. The presence of a weak intramolecular interaction between the hydrogen atom of the OH group and the oxygen atom of the adjacent SO group in methanesulfonic acid lowers its OH-stretching frequency from what would otherwise be predicted based on the electronegativity of the methyl group. [ABSTRACT FROM AUTHOR]

Vapor-phase OH-stretching overtone spectra of 1,3-propanediol and 1,4-butanediol were recorded and compared to the spectra of ethylene glycol to investigate the effect of increased intramolecular hydrogen bond strength on OH-stretching overtone transitions. The spectra were recorded with laser photoacoustic spectroscopy in the second and third OH-stretching overtone regions. The room-temperature spectra of each molecule are dominated by two conformers that show intramolecular hydrogen bonding. Anharmonic oscillator local-mode calculations of the OH-stretching transitions have been performed to aid assignment of the different conformers in the spectra and to illustrate the effect of the intramolecular hydrogen bonding. The hydrogen bond strength increases in the order ethylene glycol, 1,3-propanediol, and 1,4-butanediol. The overtone transitions of the hydrogen-bonded hydroxyl groups are more difficult to observe with increasing intramolecular hydrogen bond strength. We suggest that the bandwidth of these transitions increases with increasing hydrogen bond strength and with increasing overtone and furthermore that these changes are in part responsible for the lack of observed overtone spectra for complexes. [ABSTRACT FROM AUTHOR]

The spectroscopy of the vapor phase hydrogen bonded complex formed between methanol and trimethylamine has been studied in the near-infrared region. A combination band involving one quantum of OH stretch and one quantum of COH bend has been observed for the complex. The much less intense first OH-stretching overtone transition has been tentatively assigned. This assignment is supported by anharmonic oscillator local mode calculations. [ABSTRACT FROM AUTHOR]