VIBRATIONAL SPECTROSCOPY OF SMALL (HF)(N) CLUSTERS (N=4-8) IN SIZE-SELECTED MOLECULAR-BEAMS

Molecular beam depletion and fragment spectroscopy has been employed t o study the absorption behavior of small hydrogen fluoride clusters [( HF)(n), n=4-8] in the spectral region between 3100 and 3700 cm(-1). As tunable infrared radiation source we used an IR-seeded optical parame tric oscillator (OPO) with a LiNbO3 crystal as nonlinear medium. Size- specific information has been obtained by scattering the cluster beam from a secondary rare gas beam. Ln this way all spectral features are assigned to specific cluster sizes. While the qualitative agreement wi th earlier experiments is good, the new assignments differ by one or m ore monomer units. In general, it is found that the absorption bands m ust be assigned to larger clusters. For some cluster sizes a doublet s tructure is observed. This observation is discussed in terms of combin ation bands involving intra- and intermolecular modes; but the possibi lity of isomeric structures is considered, too. (C) 1995 American Inst itute of Physics.