The performance of the Hartree-Fock method and the three density functionals B3LYP, PBE0, and CAM-B3LYP is compared to results based on the coupled cluster singles and doubles model in predictions of the solvatochromic effects on the vertical n → * and → * electronic excitation energies of acrolein. All electronic structure methods employed the same solvent model, which is based on the combined quantum mechanics/molecular mechanics approach together with a dynamical averaging scheme. In addition to the predicted solvatochromic effects, we have also performed spectroscopic UV measurements of acrolein in vapor phase and aqueous solution. The gas-to-aqueous solution shift of the n → * excitation energy is well reproduced by using all density functional methods considered. However, the B3LYP and PBE0 functionals completely fail to describe the → * electronic transition in solution, whereas the recent CAM-B3LYP functional performs well also in this case. The → * excitation energy of acrolein in water solution is found to be very dependent on intermolecular induction and nonelectrostatic interactions. The computed excitation energies of acrolein in vacuum and solution compare well to experimental data.

SO 2 and natural abundance samples were obtained from commercial manufacturers. The spectrum of the natural abundance sample is in agreement with previously published spectra. The spectra of the isotopically pure species were retrieved using the isotopic composition of the samples. The 32 SO 2 , 33 SO 2 , and 34 SO 2 absorption spectra show rich vibrational structure, and the positions and widths of the peaks change with isotopic substitution in a complex fashion. The results imply that large wavelength-dependent and broadband isotopic fractionations are associated with the UV photolysis of SO 2 .

Nitrous oxide (N 2 O) plays an important role in greenhouse warming and ozone depletion. Yung and Miller's zero point energy (ZPE) model for the photolysis of N 2 O isotopomers was able to explain atmospheric isotopomer distributions without invoking in situ chemical sources. Subsequent experiments showed enrichment factors twice those predicted by the ZPE model. In this article we calculate the UV spectrum of the key N 2 O isotopomers to quantify the influence of factors not included in the ZPE model, namely, the transition dipole surface, bending vibrational excitation, dynamics on the excited state potential surface, and factors related to isotopic substitution itself. The relative cross-sections are calculated as the Fourier transform of the correlation function of the initial vibrational wave function and the time-propagated wave function, using a Hermite expansion of the time evolution operator. The model uses the electronic structure data recently published by Balint-Kurti and co-workers and makes several predictions. (a) The absolute values of the enrichment factors decrease with increasing temperature. (b) Photolysis of N 2 O will produce "mass-independent" enrichment in the remaining sample. (c) Much of the enrichment is due to decreased heavy isotopomer cross-section over the entire absorption band, in contrast to the wavelength shift predicted by the ZPE model. Consequently, to within the error of the calculation, we predict only minor enrichments at λ < 182 nm. The smaller bending excursion of heavy isotopomers combines with the transition dipole surface to produce a smaller integrated cross-section. This effect is partially countered by the larger fraction of heavy isotopomers in excited bending states; the first three bending states have an integrated intensity ratio of ca. 1:3:6. The model agrees with available experimental enrichment factors and stratospheric balloon infrared remote sensing data to within the estimated error.