15min:

CHENG-CHI CHUANG, SUSY N. TSANG AND WILLIAM KLEMPERER, Department of Chemistry, Harvard University, Cambridge, MA 02138; HUAN-CHEN CHANG, Institute of Atomic and Molecular Sciences, Academica Sinica, P.O.Box 23-166, Taipei, Taiwan 10764, Republic of China.

%TEXT OF YOUR ABSTRACT We report a high resolution re-examination of K=1 subband of 3₂+₆ and the 3₁+₄ (K=0) combination mode of (HF)₂ by intracavity laser induced fluorescence. The fluorescence is monitored with a germanium detector which collects only first overtone emission (2-> 0) of HF fragments. The band centered at 11537 cm^-1 is shown to be K=1 of 3₂+₆ [previously assigned to K=1 of ₁+2₂, J. Chem. Phys. 100, 1 (1994)]. Hydrogen interchange tunneling is almost completely quenched ( _t=0.6 GHz). Vibrational predissociation rate is rapid (4.5 GHz) but half that of 10 GHz observed in 3₂. The combination mode 3₁+₄ is recorded with band origins of 11402.889(4) and 11402.868(8) cm^-1 and rotational constants of 0.21639(17) and 0.21704(15) cm^-1 for the two tunneling components A⁺ and B⁺, respectively. The frequency of this intermolecular vibration, ₄, upon 3₁ excitation is 129.36 cm^-1, quite similar to that at the fundamental, suggesting only a minor dependence of the hydrogen bond vibration on the free-HF bond length. The predissociaton linewidth for 3₁+₄ mode is 2.5(2) GHz, which is one order of magnitude larger than the 0.24(2) GHz of the 3₁ state. The coupling of this state to the dark state of 3₂+₄+₅ is suggested for the origin of the observed linewidth increase.