STRUCTURAL DEPENDENCE OF HF VIBRATIONAL RED SHIFTS IN ARNHF, N = 1-4, VIA HIGH-RESOLUTION SLIT JET INFRARED-SPECTROSCOPY

The rotationally resolved upsilon = 1 <-- 0 HF stretching spectra of Ar(n)HF, n = 1-4, have been observed by using a slit jet, difference frequency infrared laser spectrometer. The red shift of the HF vibrational frequency is seen to be sensitively dependent on the placement of the Ar with respect to the projection of the HF dipole moment; the largest incremental red shift is observed for the ArHF linear geometry. The n = 1-3 red shifts account for almost half (9.65-19.26 cm-1) of the shift observed for HF in an Ar matrix (42.4 cm-1), suggesting that only the nearest neighbors contribute significantly to the perturbation of the HF vibrational frequency. The geometry of the experimentally observed isomer of Ar4HF places the fourth Ar in what would be the second coordination layer from the HF where it has little effect (< 2%) on the observed red shift, supporting the proposed dominance of the nearest neighbors in determining the HF vibrational frequency. In all spectra, no evidence for vibrational predissociation is observed, indicating an extremely long excited state lifetime (greater-than-or-similar-to 16 ns).