THE INFRARED-SPECTRUM OF NE-CO ANALYSIS OF COMBINED JET AND STATIC CELL DATA FOR NE-20 AND NE-22

The rotation-vibration spectrum of the weakly bound complex Ne-CO has been studied in the 2140 cm-1 region of the fundamental stretching vibration of carbon monoxide. Spectra were obtained using two different and complementary techniques: first, a pulsed supersonic jet expansion and a tunable infrared diode laser source; and, second, a long-path, low-temperature. static gas cell and a Fourier transform infrared spectrometer. The spectrum of Ne-CO is approximately that of a T-shaped asymmetric rotor, but the complex undergoes very large amplitude intermolecular bending and stretching motions. About 106 transitions Ne-20-(CO)-C-12-O-16, and 88 for Ne-22-(CO)-C-12-O-16, were assigned to the perpendicular subbands with K = 1 <-- 0 and 0 <-- 1 and to the parallel subband with K = 0 <-- 0. Tentative observations were also made of the K = 2 <-- 1 and 1 <-- 2 subband centres, and of a bending combination band of the Ne-20 isotope. The observed BBAR rotational constant in the K = 0 ground state was 0-10873 cm-1 for Ne-20-CO, which corresponds to an effective intermolecular separation of 3.646 angstrom. The observed A rotational constant of about 3.57 cm-1 approaches the value that would be expected in the limit of free CO internal rotation, namely 2B for CO or 3.84 cm-1.