Vibrational, rotational, and tunneling dependence of vibrational predissociation in the HF dimer

Vibrational predissociation linewidths have been resolved in the two H–F stretching bands of the HF dimer using an optothermal (bolometer-detected) molecular-beam color-center laser spectrometer. In addition to the strong vibrational mode dependence reported earlier by several groups, we observe a substantial K-rotational and tunneling dependence to the longer-lived mode ν1, which is associated with the ‘‘free-H’’ stretch. The predissociation linewidths (FWHM in MHz) for this vibration are 6.4(5) for K=0+, 9.5(5) for K=0−, 10.2(5) for K=1+, and 11.8(5) for K=1−, where the +/− superscripts refer to the symmetric/antisymmetric tunneling states. The J dependence (at low J) is negligible compared to the K dependence. The K=0 levels of the ‘‘bound-H’’ stretch have tunneling-independent widths of 330(30) MHz. Extraneous broadening due to saturation effects was observed and corrected for in these measurements.