Knowledge Bank

The inversion-rotation spectrum of HF---HF has been investigated with the RAD-3 spectrometer at Gorky (1) in the frequency range 180-380 GHz at 210 K and pressures from 0.5 to 1.5 Torr. The spectrum was reexamined in the range 60-125 GHz with a conventional Stark spectrometer at pressures of 0.1 to 0.2 Torr and at temperatures near 195 K at NIST. Altogether 19 P-, Q-, and R-branch lines of the $K=3$ a-type inversion-rotation subband have been observed. The rotational constants of this subband are somewhat anomalous as compared with the previously observed lower K subbands (2). For example, B'-B'' for this subband is positive while this difference is negative for the lower K transitions, and the Q-branch degrades to lower frequencies. The assignment, however, is well established by the missing lines in the Q- and P-branches. The inversion frequency for $K=3$ is 114 307.04(46) MHz which is in good agreement with the value of 114 790(150) MHz obtained by von Puttkamer et al. (3) from far IR studies. High J R-branch lines of the $K=O$ through $K=2$ subbands which fall in the higher frequency region have also been identified and improved rotational constants for these states obtained. (1) S.P. Belov and M.Yu. Tretyakov, IX Int. Conf. on High Res. IR Spectrosc., Prague, 68 (1986). (2) W.J. Lafferty, R.D. Suenram, and F.J. Lovas, J. Mol. Spectrosc. 123, 434 (1987). (3) K. von Puttkamer, M. Quack, and M.A. Suhm, Mol. Phys., in press.