Observation of strong hidden lines in the infrared spectrum of the CO–He complex

Abstract

In the only previous observation of spectra of the weakly bound complex CO–He [C. E. Chuaqui, R. J. Le Roy, and A. R. W. McKellar, J. Chem. Phys. 101, 39 (1994)], only 6 out of the 21 strongest transitions were observed, and much of the analysis therefore relied on relatively weak transitions. These strong ‘‘hidden’’ transitions are located very close to, and were obscured by, pressure-broadened transitions of the CO monomer. In the present paper, the measurement of all but one of the 15 hidden transitions has been achieved by using a sensitive tunable diode laser probe which allows much lower sample pressures. The results fully confirm the previous analysis, and provide additional precise data on the bound energy levels of this fundamental molecular system, especially for the CO–3He isotope.