Rotational spectrum and molecular structure of OCS–N2O

Abstract

The rotational spectra of four isotopomers of OCS–N2O, including nuclear quadrupole hyperfine structure in the N14-containing isotopomers, have been observed in the 6.5–19 GHz region with a Fourier transform microwave spectrometer and analyzed using the Watson A-reduced Hamiltonian with the inclusion of nuclear quadrupole coupling interactions where applicable. The effective structure of the complex, obtained by fitting the structural parameters to the moments of inertia of each isotopomer, is approximately slipped parallel, with oxygen in N2O and sulfur in OCS occupying the obtuse vertices of the quadrilateral formed by the two subunits. The intermolecular distance is 3.5166(2) Å, with N2O and OCS forming angles of 68.5(3)° and 99.6(2)° with the intermolecular axis, respectively. This structure is also supported by a Kraitchman analysis. Comparisons of the structure of OCS–N2O with those of OCS–CO2 and CO2–N2O show that the isoelectronic N2O and CO2 behave similarly in their intermolecular interactions with OCS while the difference between the isovalent OCS and CO2 in their interactions with N2O mainly arises from steric effects. The nuclear quadrupole coupling constants of the two nitrogen nuclei in OC32S–14N2O do not definitively indicate a perturbation of the electronic distribution of N2O in the complex. However, an electrostatic calculation of the electric fields at the N2O atomic positions due to OCS shows that the perturbation is small and is therefore rendered unobservable due to the large uncertainties in the nuclear quadrupole coupling constants of the central nitrogen.