New infrared bands of nonpolar OCS dimer and experimental frequencies for two intermolecular modes

摘要

Spectra of the nonpolar carbonyl sulfide dimer in the region of the OCS ν _1 fundamental band were observed in a slit-jet supersonic expansion. The jet was probed using radiation from a tunable diode laser employed in a rapid-scan signal averaging mode. Six new bands were observed and analyzed, all of which originate from the dimer ground vibrational state. Three were vibrational fundamentals involving the (~(18)OCS) _2 and ~(16)OCS- ~(18)OCS isotopologues. They enabled an estimate to be made of the frequency of the infrared-forbidden mode corresponding to in-phase vibration of the OCS monomers in the dimer, a value needed to obtain an intermolecular vibrational frequency from one of the observed combination bands. A relatively weak b-type dimer band centered at 2103.105 cm ~(-1) was assigned to the OCS 4ν _2 (l 0) bending overtone. Combination bands were observed involving the geared bend and van der Waals stretch intermolecular modes. The resulting experimental frequencies of 37.5(20) cm ~(-1) for the bend and 42.9727(1) cm ~(-1) for the stretch are in good agreement with a recent high level theoretical calculation.