INFRARED-SPECTRUM OF C2H2-N2 AND C2H2-CO IN THE C-H STRETCHING REGION - EXAMPLES OF MULTIPLE COUPLING OF STATES IN A NEAR CONTINUUM OF STATES

The infrared spectra of the linear van der Waals molecules C2H2-N2 and C2H2-CO have been measured in a nozzle-beam apparatus with a rotational temperature of about 1.5 K. The spectrum consists of transitions from a single ground vibrational state to many different vibrational upper states. For both molecules a single vibrational transition, due to the CH stretching fundamental, is responsible for the transition moment. Interactions between that state and other nearby "dark" states gives rise to the observed multiline spectrum. Many of the extra lines seem to come from weak resonances that are active only for the one or two J-levels where the CH fundamental crosses another vibrational state. These van der Waals molecules, which have two or three fundamental vibrational modes below 50 cm-1, show the complicated spectrum that can be expected when a single vibrational state interacts with a few of the states that form a near-continuum at 3280 cm-1. From the analysis, the van der Waals stretching frequencies are estimated. © 1993 Academic Press, Inc.