Tunable diode laser study of the (nu)3 band of oxirane

Theoretical values of vibrational frequencies and rotational constants for all the isotopomers of nitrous oxide are reported. The calculations are carried out variationally using an empirical Morse-cosine potential energy surface previously determined for N2O, and a set of optimal internal vibrational coordinates. The spectroscopic constants obtained are compared to those extracted from spectroscopic measurements for the ..., and 14N218O isotopomers. The agreement between calculated and observed values for these isotopomers is shown to be excellent, especially for the rotational constants. As a result, an unidentified band recently recorded is properly assigned. The spectroscopic constants computed for the rest of the isotopomers, for which observed information is much scarcer, have therefore a predictive character. The vibrational zero point energies for all the N2O isotopomers are also given.