Abstract
Five distinct species of OCS–hydrogen van der Waals complexes (OCS–orthoH2,–paraH2,–paraD2,–orthoD2, and –HD) have been observed by infrared spectroscopy in the region of the OCS ν1 vibration (≈2062 cm−1) in a pulsed supersonic jet expansion using a tunable diode laser probe. The spectra are those of prolate asymmetric rotors, with observed a-type transitions (ΔK=0), but no b-type transitions (ΔK=±1). The fitted rotational parameters are consistent with structures having intermolecular separations in the range of 3.6–3.8 Å and angles of about 70° between the OCS axis and the hydrogen center of mass. The band origins are slightly red-shifted (−0.05 to −0.20 cm−1) relative to that of the free OCS molecule. The results are of interest due to recent observations of the same complexes trapped in ultracold helium droplets; there is a remarkably close correspondence of the vibrational band origins of the free and trapped species.
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