Experimental HR FTIR studies of the stability of the hydrogen chloride complexes with ethylene and acetylene

A high resolution FTIR study of intermolecular interactions in van der Waal s dimers, HCl-ethylene and HCl-acetylene, has been carried out. Partly reso lved vibration-rotation spectral bands of the complexes are observed in the spectral region 2795-2820 cm(-1). Assignments of the vibrational spectral bands are made combining ab initio data with the experimental results. It i s concluded that the very unsymmetrical shape of the P branches of A-type b ands is due to an increase of the rotational constants B and C in the first vibrationally excited state of the HCl stretch of the complexed HCl. The a b initio calculations predict the existence of low wavenumber intermolecula r fundamental vibrations whose first excited states have significant popula tions at the temperatures of the measurements. Hot bands due to these funda mentals have been observed in the spectra, (C) 2001 Elsevier Science B.V. A ll rights reserved.