MOLECULAR BEAM INFRARED SPECTRUM OF THE HF STRETCHING FUNDAMENTAL BAND OF THE HF-$BF_{3}$ COMPLEX

$^{j}$. A. Philips, M Canagagar, H. Goodfriend, H. Grushow, J. Almlof and K.R Lepold J. Am. Chem. Soc. 117, 12459 (1995).Author Institution: Dept. of Chemistry, University of North Carolina; Optical Technology Division, NISTThe microwave spectrum of the anti hydrogen bonded $HF-BF_{3}$ complex has recently been reported by Philips at $al^{h}$. The spectrum reveals a near symmetric $F-BF_{3}$ heavy atom frame with the proton slightly off axis, and a small barrier to internal rotation of the H atom against the F atoms. HERE WE HAVE Investigated the H-F stretching fundamental band of this complex using a molecular beam optothermal spectrometer and a color center laser. Two subbands are expected: a parallel band with $\Delta m = 0$ selection rules and a perpendicular band with $\Delta m = \pm 1$ selection rules. At present, only the perpendicular band has bran observed. This band has the appearance of a perpendicular band of a symmetric rotor, but with anomalously strong R transitions and weak P transitions. Upper state constants are obtained fixing the ground-state constants to the microwave determined values. The band has a large positive $\zeta$ Coriolis constant from which an estimate of the barrier to internal rotation can be mode. A search is presently underlay to locate the expected weaker $\Delta m=0$ parallel component