Matrix effect found in the reaction of GaCl with HCl: application of the Onsager model to describe interactions between matrices and matrix isolated species

The matrix photochemistry of the GaCl/HCl system is re-examined applying de nsity functional theory (DFT) calculations. First, the structure of the pri mary hydrogen bonded complex (GaCl . HCl) is presented, which allows the hi ghly subcoordinated GaCl to partially fill up its coordination sphere relea sing 2.1 kcal mol(-1) of reaction enthalpy. This is one of the rare cases t hat a preformed complex in an rare gas cage can be unequivocally characteri sed by spectroscopic and structural methods before reacting to its final pr oduct. For all further species (GaCl, Ga2Cl2, HGaCl2) accurate geometries, energies and IR spectra are derived as well. Second, the remaining differen ces between experiment and theory are reconciled by considering the solvati on effects of the matrix material used. The Onsager theory applied to this particular photoreaction can explain the significant change of the IR frequ ency of GaCl observed in the gas phase (vGaCl = 352 cm(-1)) and in 'weakly' solvating rare gas matrices (vGaCl = 329 cm(-1)). Thus, a valuable method for improving the interpretation of matrix isolation IR data is demonstrate d. (C) 1999 Elsevier Science B.V. All rights reserved.