VIRATIONAL, ROTATIONAL, AND TUNNELING DEPENDENCE OF VIBRATIONAL PREDISSOCIATION IN THE HF DIMER

$^{1}$ A. S. Pine and W.J. Lafferty, J. Chem. Phys. 28, 2154 (1983). $^{2}$ A. S. Pine, W. J. Lafferty. and B. J. Howard, J. Chem. Phys. 81, 2939 (1984). $^{3}$ Z. S. Huang. K. W. Jucks and R. E. Miller. J. Chem. Phys. 85, 3338 (1986).Author Institution: Molecular Spectroscopy Division, National Bureau of StandardsAs observed $previously^{1-3}$, 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 ($\pm 0.5 MHz$). 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 $blending^{1-2}$ afforded by the low effective temperatures of the adiabatic expansion