The emission spectroscopy of acrolein ͑C 3 H 4 O͒, acrylic acid ͑C 2 H 3 COOH͒, and acryloyl chloride ͑C 2 H 3 COCl͒ excited at 199 nm elucidates the dominant electronic character of the excited state reached by the optical transition at this wavelength. Progressions in the CvC and CvO stretching overtones and various combination bands suggest the antibonding orbital has mixed *͑CvC͒/*͑CvO͒ character. We interpret the results in conjunction with ab initio calculations at the configuration interaction singles level to identify the influence of resonance in the excited state of these conjugated molecules. The results on acrylic acid are of particular interest as excitation in this absorption band produces the HOCO intermediate of the OHϩCO→HϩCO 2 reaction that is important in combustion.

This work investigates the predissociative C̃(11B2) state of SO2 by cooling the SO2 in a pulsed molecular beam and dispersing the emission upon resonant excitation into several different vibronic absorption features in the C̃ state between 197 and 212 nm. Unlike at the lower excitation energies, the dispersed emission spectra at the higher excitation energies are dominated by progressions with odd quanta in the antisymmetric stretch mode ν3 and combination bands with up to six quanta in the bending mode ν2. The formidable intensity for emission into vibrational states with odd quanta in the antisymmetric stretch of the jet-cooled molecule suggests that the intermediate state at high energies in the excited state is of mixed electronic character at nonsymmetric geometries, so the operative components of the transition moment for excitation and emission may be different. We discuss our results by considering the avoided crossing seam and coupling between the C̃(11B2) state and two dissociative states potentially involved in the electronic predissociation, the 3 1A1 and the 1 3A1 states.

We report the emission spectra of dissociating vinyl, allyl, and propargyl chloride upon photoexcitation at 199 nm. To provide a better understanding of the mixed electronic character in the Franck-Condon region of the excited states accessed, we also present ab initio calculations at the configuration interaction level for these three molecules. These experimental and theoretical results indicate large differences in the contribution of nσ* C-Cl and πσ* C-Cl character to these predominantly ππ* CdC/CtC transitions. We present arguments based on the symmetry of the pertinent molecular orbitals to explain this observed variation. We conclude by considering how the differing electronic character of the excited state in these molecules may influence the branching ratios to C-Cl fission and HCl elimination products observed in the photodissociation of vinyl, allyl, and propargyl chloride.

Articles you may be interested inGlobal threedimensional potential energy surfaces of H2S from the ab initio effective valence shell Hamiltonian method Electron spin resonance matrix isolation and ab initio theoretical investigations of 69,71GaH2, 69,71GaD2, H69,71GaCH3, and D69,71GaCD3 Solvent effects on DielsAlder reactions: ab initio versus density functional theory AIP Conf. Proc. 330, 76 (1995); 10.1063/1.47855On the role of conical intersections of two potential energy surfaces of the same symmetry in photodissociation. I. CH3SH→CH3S+H and CH3+SHThe ground and first and second I A" potential surfaces of methyl mercaptan (CH 3 SH) are calculated as a function of the C-S and S-H bond coordinates using the ab initio effective valence shell Hamiltonian (HV) method. The computations for this highly nontrivial system provide the first serious tests for choosing restricted valence spaces and for computing global potential energy surfaces with the H V methods. The quasidegeneracy constraints on the H V method suggest choosing a valence space which consists of the two (3a" and lOa') highest energy occupied orbitals in the ground state and the three lowest a' unoccupied orbitals. The global potential surfaces are computed with a modest basis, but larger basis set computations at selected geometries test convergence for vertical excitation energies, ionization potentials, and C-S and S-H bond energies. The calculations are compared to both experiment and other calculations for this system. The computations assist in the interpretation of CH 3 SH photodissociation dynamics observed by Butler and co-workers.4832

Resonance enhanced multiphoton ionization spectroscopy of jet cooled 12 C 32 S 2 and 12 C 34 S 32 S from 45 500 to 48000 cm−1