RESONANCE-ENHANCED MULTIPHOTON IONIZATION SPECTROSCOPY OF CARBONYL SULFIDE

Rydberg excited states of the OCS molecule in the energy range 70500-8 6000 cm(-1) have been investigated via the two and three photon resona nce enhancements they provide in the mass resolved multiphoton ionizat ion (MPI) spectrum of a jet-cooled sample of the parent molecule. Spec tral interpretation has been assisted by companion measurements of the kinetic energies of the photoelectrons that accompany the various MPI resonances. The present study supports the earlier conclusions of Wei nkauf and Boesl [J. Chem. Phys. 98, 4459 (1993)] regarding five Rydber g origins in the 70500-73000 cm(-1) energy range, attributable to, res pectively, states of (II)-I-3, (II)-I-1, (3) Delta, (1) Delta and (1) Sigma(+) symmetry arising from the 4p lambda <-- 3 pi orbital promotio n. We also identify a further 21 Rydberg origins at higher energies. T hese partition into clumps with quantum defects ca. 3.5 and 4.5, which we associate with the orbital promotions np lambda <-- 3 pi (n = 5,6) , and others with near integer quantum defect which are interpretable in terms of excitation to s,d and (possibly) f Rydberg orbitals. We al so identify MPI resonances attributable to CO(X (1) Sigma(+)) fragment s and to S atoms in both their ground ((3)p) and excited (D-1) electro nic states. Analysis of the former resonances confirms that the CO(X) fragments resulting from one photon dissociation of OCS at excitation wavelengths ca. 230 nm are formed with a highly inverted, bimodal rota tional state population distribution, whilst the latter are consistent with previous reports of the wavelength dependence for forming ground and excited state S atoms in the near uv photolysis of OCS. (C) 1996 American Institute of Physics.