Determination of the structures of benzotriazole(H2O)1,2 clusters by IR–UV spectroscopy and ab initio theory

Abstract

The structures of benzotriazole monomer and benzotriazole(H₂O)_1,2 clusters have been examined by comparison of R2PI spectra and IR–UV double resonance spectra with the results of ab initio based normal mode calculations. The structures of the binary benzotriazole–water cluster and the n = 2 cluster are shown to be cyclic. Based on these cyclic structures the intermolecular vibronic transitions have been assigned by comparison with ab initio normal mode analysis. The cyclic benzotriazole(H₂O)_1,2 clusters can be viewed as a precursor to a transition state for H-atom transfer from the 1- to the 2-position in benzotriazole. The activation energy for this tautomerism has been calculated for the monomer and the n = 1 and 2 cluster as the difference between the stabilization energy of the more stable tautomer and the respective transition state. It has been found to decrease rapidly, with increasing cluster size.