Isotope effects in the infrared spectrum of the OCS dimer

Infrared spectra of 34S and 13C isotopes of the OCS dimer are studied in the 2015–2075 cm−1 region using a tunable laser to probe a pulsed supersonic expansion. The spectrum of (16O12C34S)2 is similar to that of the normal isotope, but that of (16O13C32S)2 differs due to nuclear spin statistics and due to small (<0.01 cm−1) rotational perturbations whose nature is not entirely clear. The shift of the (16O13C32S)2 band origin relative to 16O13C32S is significantly smaller than predicted by scaling from the normal isotope. It was not possible to detect spectra of isotopically mixed dimers.