Dynamical charge transfer through hydrogen bonds: Hartree–Fock calculations of vibrational properties of formic acid monomer and cyclic dimer

Abstract

In order to explain the observed changes in the vibrational spectra of formic acid from monomeric to cyclic dimeric form the SCF Hartree–Fock method has been applied to calculate minimum energy geometries, quadratic force constants, and net atomic charges. The set of ab initio quadratic force constants turns out to be acceptable and accounts for the observed vibrational changes. The ab initio interaction force constant between carbonyl stretching motions for the dimer accounts for what is considered to be an unusually large observed splitting of the C=O stretching frequencies in carboxylic acid dimers. Calculations suggest that such a large splitting originates from a dynamical charge transfer through the hydrogen bond. The possible existence of this phenomenon should in general be considered when dealing with the vibrational properties of hydrogen bonded systems.

Compliant fields for molecular interactions: Water dimer and formic acid dimer

“…The value as obtained in the present study is Table V. 11.476 mdyn k' may be compared with the value 9.6 mdyn A-' obtained by Alfheim et al [22] after suitable conversion of their symmetry force constants to internal force constants. On the other hand, Bosi et al [23] have calculated Fc=o to be 13.42 mdyn A-' in their ab initio study. The other stretching force constants evaluated in this study compare well with those of Alfheim et al [22] and Bosi et al [23].…”

“…On the other hand, Bosi et al [23] have calculated Fc=o to be 13.42 mdyn A-' in their ab initio study. The other stretching force constants evaluated in this study compare well with those of Alfheim et al [22] and Bosi et al [23].…”

“…A complete experimental symmetry valence force field for formic acid dimer based on the diagonal values for the intramolecular coordinates, has been evaluated by Alfheim, Hagen, and Cyvin [22]. A few diagonal force constants of formic acid dimer have been evaluated using ab initio wave functions by Bosi, Zerbi, and Clementi [23]. Force field calculations on the dimeric form of formic acid have been attempted at the CND0/2 level by Marmar, Pouchan, and Chaillet [24].…”

Absorption of the C  H Stretching Fundamentals in Pure Ethylene to High Pressures and Temperatures

“…These considerations, Schematic representation of the variation of the bond dipole so far, apply to isolated molecules. Attractive intermolecular forces in polar materials increase the bond polarity, as has been demonstrated in quantum-mechanical calculations on dimers of water [21], ammonia [22], and formic acid [23] molecules. The integrated molar absorptivity of the stretching modes which, to a first crude approximation, is proportional to (api/ari)2 thus should increase with density.…”

“…Experiments to high pressures at supercritical temperature are especially advantageous as they enable spectra to be obtained at continuous density variation from gaseous to liquid-like states [ 1, 23. Measurements on polar materials, such as water [i], hydrogen chloride [2], and ammonia [3,4] revealed large changes of the bandshape, the integrated molar absorptivity, and the position of the stretching band maxima due to pressure and temperature variations.…”