Nonlinear dipole-dipole interactions and spectroscopic properties of van der Waals complexes in the gas phase

We suggest a semiempirical approach to describing the influence of local nonlinear dipole-dipole interactions on the formation of van der Waals complexes of 1:1 composition in the gas phase. Based on this approach, we quantitatively interpret the experimental data on the patterns of the shift in the electronic (complexes of a 3-aminophthalimide molecule with water and methanol molecules) and vibrational (complexes of a HCl molecule with acetone and acetonitrile molecules) absorption spectra attributable to the processes of complex formation. We confirm the conclusion that a nonlinear dipole-dipole interaction should be considered as one of the most important physical mechanisms that result in the association of molecules both in the gas phase and, under certain conditions, in the condensed state. (C) 2003 MAIK "Nauka/Interperiodica".