Calculation of the structure and IR absorption spectra of hydrogen-bonded complexes of methyl formate with hydrogen fluoride

Equilibrium nuclear configurations of three dimers formed by the most stable conformer of a methyl formate molecule with a hydrogen fluoride molecule are calculated using the MP2/aug-cc-pVTZ quantum-chemical method and taking the basis set superposition error into account. The frequencies and intensities for the IR absorption bands of dimers are determined both in the harmonic and anharmonic approximations with the use of the second-order perturbation theory. The calculation method was tested in a calculation of the spectrum of an isolated methyl formate molecule and by comparison with experimental data. The changes in the geometrical parameters of monomers and the charges on atoms under the action of hydrogen bonds were analyzed. The shifts of vibrational frequencies of the monomers upon formation of dimers were calculated. The strongest absorption bands of dimers that can be used in detection of these complexes in spectroscopic experiments were determined.