Trimers formed by methyl formate with hydrogen fluoride: Structures, energetics, and infrared absorption spectra

Equilibrium nuclear configurations of three stable HCOOCH₃∙∙∙(HF)₂ trimers are calculated in the MP2/aug-cc-pVTZ approximation with the basis set superposition error taken into account. Anharmonic values of frequencies and intensities for infrared absorption bands are computed with the help of a second-order perturbation theory. The changes in the structural and spectral parameters upon formation of trimers are examined by comparing the results obtained for the trimers with analogous parameters of dimers and isolated molecules calculated earlier in the same approximation. Cooperativity of H-bonding effects in trimers and the correlations between the intramolecular and intermolecular charge transfer, the structural and spectral changes upon formation of trimers are analyzed. The frequency and intensity values are predicted for sufficiently strong absorption bands, which can be used to detect these trimers by spectroscopic methods.