OBSERVATION AND ASSIGNMENT OF THE HYDROGEN-BOND EXCHANGE DISROTATORY INPLANE BENDING VIBRATION-NU-5 IN (HF)2

We report far-infrared spectra between 100 and 300 cm-1 for (HF)2 under equilibrium conditions in hydrogen fluoride vapour (243 K, 1.2-1.7 kPa). The spectra were obtained by high-resolution interferometric Fourier transform techniques (resolution 0.007 to 0.012 cm-1 fwhm unapodised) using a new 2.6 m high transmission light pipe cell and a 10 m long path cell. The K = 3, A+ sublevel of the large-amplitude disrotatory in-plane bending fundamental v5 of (HF)2 is assigned at 393.550 cm-1 by analysis of the perpendicular K = 3 ← 2 subband near 275.4 cm-1 and the parallel K = 3 ← 3 subband near 157.1 cm-1. The results are compared with recent theoretical predictions. © 1990.