Microwave spectrum of the N2O-SO2 dimer: Evidence for tunneling and an asymmetric structure

The microwave spectrum of the nitrous oxide-sulfur dioxide complex has been investigated. The dimer differs from similar complexes of SO2 with a linea r molecule in that it lacks a symmetry plane. A tunneling motion splits the transitions into doublers. This is attributed to an interconversion betwee n mirror-image conformations in which the oxygen atoms on the SO2 are inequ ivalent. The rotational constants for the normal species are A = 6126.9781( 15) MHz, B = 1494.537(37) MHz, and C = 1435.474(36) MHz fur the higher freq uency component of the doublets and A = 5500 MHz (fixed), B = 1463.483(33) MHz, and C = 1420.953(23) MHz for the lower frequency component. Spectra fo r four isotopomers in addition to the normal species have been measured, an d the dipole moment of the complex has been determined to he 1.212 D. A sem iempirical model with atom-atom interaction terms is consistent with an asy mmetric equilibrium structure.