Millimeter-wave detection of doubly excited bending mode in the CO–N2 van der Waals complex

Abstract

A millimeter-wave intracavity OROTRON spectrometer in combination with a pulsed supersonic pin-hole jet expansion has been used to record a new subband of the CO–N2 weakly bound van der Waals complex in the 100–150 GHz region. Seven lines were assigned to the K = 0–0, (jCO, jN2) = (2, 0)–(1, 0) “hot band” transitions to a thus far unobserved K = 0 state at 9.336 cm−1 above the ground state. This is the highest in energy van der Waals mode detected so far, and this mode may be interpreted as a doubly excited bending vibration of the CO–orthoN2 nuclear spin isomer. Hyperfine structure caused by two 14N nuclei was partly resolved for the measured lines, and the quadrupole coupling constant, associated with the N2 subunit, together with rotational and centrifugal distortion parameters were precisely determined for the new K = 0, (jCO, jN2) = (2,0) state. The high lying energy levels of this state provided a sensitive test for the recent ab initio potential energy surfaces.