Molecular beam photoionization study of OCS, (OCS)2, (OCS)3, and OCS⋅CS2

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Abstract
Photoionization efficiency (PIE) data for OCS+ near the threshold (1080–1111 Å) were obtained with a resolution of 0.14 Å (FWHM) using the molecular beam method. The ionization energies (IE) for the 2Π3/2 and 2Π1/2 states of OCS were determined to be 11.1736±0.0015 eV (1109.62±0.15 Å) and 11.2204±0.0015 eV (1104.95±0.15 Å), respectively. These values are found to be in agreement with those obtained in previous photoionization experiments. PIE data for (OCS)2, (OCS)3, and OCS⋅CS2 have also been obtained in the wavelength region 750–1270 Å. The observed IE’s for (OCS)2, (OCS)3, and OCS⋅CS2 are 10.456±0.026, 10.408±0.026, and 9.858±0.024 eV, respectively. From the measured IE’s and the estimated dissociation energies of (OCS)2 and OCS⋅CS2, the binding energies for OCS+⋅OCS and CS+2⋅OCS are deduced to be 17.2±1 and 5.8±1 kcal/mol, respectively. From the shifts in energy of the Rydberg series of CS2 and OCS in the OCS⋅CS2 and (OCS)2 dimers, and from the symmetry of the Rydberg orbitals, possible geometries for OCS⋅CS2 and (OCS)2 are discussed.