High resolution absorption spectrum of jet-cooled OCS between 64 000 and 91 000 cm−1

Abstract

The absorption spectrum of jet-cooled OCS was photographed from 190 to 110 nm at a resolution limit of 0.0008 nm. No band maximum was observed between 190 and 156 nm, i.e., below 64 000 cm−1. Ab initio calculations of the electronic energies and transition moments were carried out, including spin–orbit interaction, in the frozen core approximation. Rydberg states considered have ionic core X̃ 2Π and principal effective quantum number n*=2–5.5, electronic angular momentum l=0–5. Up to n*=3.5, l=0–2, calculations were also done in the coupled electron pair approximation. It is shown that in OCS, like in N2O, CO2 or CS2, npπ 1Σ+ states are at lower energy than npσ1,3Π. From the doublet structure shown by the corresponding transition origin bands, the rotational constant of the 4pσ1,3Π and 4pπ 3Σ− states was deduced to be B0′=0.1940(5) cm−1. Transitions involving excitation to ns or nd Rydberg orbitals, allowed in the less-symmetric molecules, were calculated to have relative intensities respectively two and three orders of magnitude greater in OCS than in N2O. The ns series could be assigned only to medium intensity or weak bands. In contrast, ndδ1Π transitions were assigned to relatively strong bands and could be followed up to n about 20. Previous low-resolution absorption and electron-impact spectra are reviewed. Most of the present assignments agree with those of resonance enhanced multiphoton ionization spectra and satisfactory assignments are obtained for the 15 unassigned electronic origins observed by Morgan et al. [J. Chem. Phys. 105, 2141 (1996)].