Knowledge Bank

An infrared absorption spectrum of jet-cooled (3K) 1-butyne is recorded by monitoring the attenuation of a scanned single-mode F-center laser beam. Rigorous are made by comparison of combination-differences with microwave data on this near-prolate asymmetric top. Levels with $K-1=0$ are heavily mixed for all J and appear as a clump of 4 or more. The density of coupled states approximates the calculated total density of vibrational states $(-60percm-1)$. The $K-1=1$ levels are apparently unperturbed for $J\le 3$ but heavily mixed for higher $J(\ge 7)$. The little information available on $K-1=2$ indicates that it is strongly mixed even for low J. As compared to $K-1=0,2,K-1=1$ is anomolously noninteractive with the bath of vibrational levels. From a kinetic point of view, the data provide a detailed picture of collisionless intramolecular vibrational redistribution (IVR) in the energy region where it is ``turning on''.