Knowledge Bank

The weakly bound complex NeHF is observed for the first time. Infrared absorption spectra are obtained and analyzed for the HF stretching fundamental and for the $\Pi$ bend combination band. The combination band is approximately an order of magnitude more intense than the fundamental, signalling nearly free internal rotation of the HF subunit within the complex. There are three bending states which correlate with J-1 HF rotation in the free molecule limit; the three states have widely different rotational prediasociacion rates. Prediseociation of the $\Pi 1$ levels of the perpendicular bend is symeetry forbidden at these vibrational energies. and indeed the Q branch transitions which access those states exhibit lifetimes of $\ge 25$ nsec. i.e. in excess of the instrument resolution. In contrast, J-depandent life-time broadening is observed for the P and R branch transitions which access the 1e levels of the perpendicular bend; predissociation lifetimes range from 2.7 nsec for $J\prime -1$ to 0.3 nsec for $J\prime -5$. This is discussed in terms of Corfolis mixing of the $\Pi e$ levels with the $\Sigma$ bend, which is not directly observed but which is inferred to have a predissociation lifetime of $\le 8$ psec. Scattering $calculations1$ on a recently obtained ab initio potential energy $surface2$ predict the observed results nearly quantitatively.