The i.r. spectra of benzotriazole have been measured from 4000 to 60 cm-1: polarized spectra of single crystals have been also obtained. The Raman spectra of polycrystalline samples and solutions have been investigated. The structural parameters and vibrational frequencies have been detennined from ab-inirio Hartree-Fock gradient calculations using the 6-31G* basis set. A detailed assignment of most of the observed bands has been proposed on the basis of the i.r. dichroism, Raman polarization data and frequency calculations.

The bond and molecular polarizabilities are studied for the gas-phase metal halides using delta-function potential model of chemical binding on the basis of quantum mechanical approach. The applicability of the model is demonstrated. The contribution of the polarity corrections for the metal halides is thoroughly investigated and it has been found that it plays a significant role for fluorides. Our polarizability calculations resolve the discrepancy about the conformation of the barium dichloride and mercury dichloride and favour the nonlinear structure. Due to lack of experimental results for most of halides of transition metals, the decision whether to incorporate polarity corrections or not remains uncertain at this stage: we must await measurements of more experimental values before we reach any final conclusion. The ionic bond orders have been used for the first time to investigate polarizabilities of monomers and dimers of alkali halides. The results for dimers reveal that polarity contribution is essential for the lithium halides dimers and not for other dimers. The computed results will be asset for the interpretation of experimental measurements.