Vibrational spectroscopic signatures of hydrogen bond induced NH stretch-bend Fermi-resonance in amines: The methylamine clusters and other N-H »N hydrogen-bonded complexes
Journal
Journal of Chemical Physics
Journal Volume
153
Journal Issue
19
Pages
194301
Date Issued
2020
Author(s)
Abstract
The appearance of multiple bands in the N-H stretching region of the infrared spectra of the neutral methylamine dimer and trimer is a sign of NH bend-stretch anharmonic coupling. Ab initio anharmonic calculations were carried out in a step-wise manner to reveal the origin of various bands observed in the spectrum of the methylamine dimer. A seven-dimensional potential energy surface involving symmetric and asymmetric stretching and bending vibrations of both the hydrogen bond donor and the acceptor along intermolecular-translational modes was constructed using the discrete variable representation approach. The resulting spectrum of the dimer shows five bands that can be attributed to the symmetric stretching (彖symD), asymmetric stretchin (彖asymD), and bending overtone (2彖bendD) of the donor moiety. These appear along with the combination band arising out of bending vibrations of the donor and acceptor (彖bendD + 彖bendA) and with the combination of the intermolecular translational mode over the donor bending overtone (彖trans + 2彖bendD). The spectrum of the trimer essentially consists of all the features seen in the dimer with marginal changes in band positions. The analysis of the experimental spectra based on the two-state deperturbation model and ab initio anharmonic calculations yield a matrix element of about 40 cm-1 for the N-H bend-stretch Fermi resonance coupling. In general, the IR spectra of the hydrogen-bonded amino group depict three sets of bands that arise due to bend-stretch Fermi resonance coupling. ? 2020 Author(s).
Other Subjects
Amines; Calculations; Complexation; Dimers; Potential energy; Quantum chemistry; Resonance; Stretch Forming; Anharmonic couplings; Asymmetric stretching; Discrete variable representation; Experimental spectra; Fermi-resonance coupling; Hydrogen bond donors; Hydrogen-bonded complexes; Spectroscopic signatures; Hydrogen bonds
Type
journal article