Knowledge Bank

As observed $previously1-3$, there is a marked vibrational dependence to the vibrational predissociation rate in the HF dimer with the free-H stretching mode, $\nu 1$, much longer lived than the bound-H stretching mode, $\nu 2$. Using an optothermal (bolometer-detected) crossed molecular-beam color-center laser spectrometer, we have achieved sufficient resolution to measure the narrow homogeneous linewidths for the $\nu 1$ band with high precision ($\pm 0.5MHz$). We observe a substantial K, but negligible J. dependence for the $\nu 1$ predissociation linewidths, and a smaller, but statistically significant, dependence on the tunneling state. For the symmetric lower tunneling level of $\nu 1$, the $K=1$ predissociation linewidths are almost twice as broad as the $K=0$. The widths for the antisymmetric tunneling level are roughly 50% greater than for the symmetric level for $K=0$ and about $20\%$ for $K=1$. We also report improved measurements of the broader $\nu 2$ band predissociation linewidths with reduced spectral congestion and $blending1-2$ afforded by the low effective temperatures of the adiabatic expansion.