Free-jet infrared absorption spectroscopy of rare gas–11BF3 complexes in the 7 μm region

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Abstract
High-resolution infrared absorption spectra of the van der Waals complexes of BF3 with a rare gas atom (Ne, Ar, and Kr) are obtained near the ν3 band of BF3 monomer in a supersonic free jet. Each spectrum shows a characteristic perpendicular band of a symmetric-top molecule with C3v symmetry. The bands are shifted toward the red with respect to the monomer band by 0.3933(4), 1.7609(1), and 2.4059(4) cm−1 for NeBF3, ArBF3, and KrBF3, respectively. The Coriolis coupling constants of the complexes are almost identical to that of the monomer. These results show that complexing with a rare gas atom does not strongly influence the ν3 vibrational motion in BF3. The observed red shifts correlate well with the polarizabilities of the rare gas atoms. This finding is explained in terms of the instantaneous dipole–induced dipole interaction. The observed full widths of the Doppler-limited spectral lines, typically 70 MHz, indicate that the lower limit of the vibrational predissociation lifetime is 2 ns.