Quantum Theory of Atoms in Molecules Charge-Charge Transfer-Dipolar Polarization Classification of Infrared Intensities

Author(s)

Duarte, Leonardo J. ^[1] ; Richter, Wagner E. ^[2] ; Silva, Arnaldo F. ^[3] ; Bruns, Roy E. ^[1]

Affiliation

^[1] Univ Estadual Campinas, Chem Inst, CP 6154, BR-13083970 Campinas, SP - Brazil

^[2] Technol Fed Univ Parana, Dept Chem Engn, BR-84016210 Ponta Grossa, Parana - Brazil

^[3] Univ Manchester, Manchester Inst Biotechnol, 131 Princess St, Manchester M1 7DN, Lancs - England

• Document type: Journal article
• Source: Journal of Physical Chemistry A; v. 121, n. 42, p. 8115-8123, OCT 26 2017.
• Web of Science Citations: 2

Abstract

Fundamental infrared vibrational transition intensities of gas-phase molecules are sensitive probes of changes in electronic structure accompanying small molecular distortions. Models containing charge, charge transfer, and dipolar polarization effects are necessary for a successful classification of the C-H, C-F, and C-Cl stretching and bending intensities. C-H stretching and in-plane bending vibrations involving sp(3) carbon atoms have small equilibrium charge contributions and are accurately modeled by the charge transfer-counterpolarization contribution and its interaction with equilibrium charge movement. Large C-F and C = O stretching intensities have dominant equilibrium charge movement contributions compared to their charge transfer dipolar polarization ones and are accurately estimated by equilibrium charge and the interaction contribution. The C-F and C-Cl bending modes have charge and charge transfer dipolar polarization contribution sums that are of similar size but opposite sign to their interaction values resulting in small intensities. Experimental in-plane C-H bends have small average intensities of 12.6 +/- 10.4 km mol(-1) owing to negligible charge contributions and charge transfer-counterpolarization cancellations, whereas their average out-of-plane experimental intensities are much larger, 65.7 +/- 20.0 km mol(-1), as charge transfer is zero and only dipolar polarization takes place. The C-F bending intensities have large charge contributions but very small intensities. Their average experimental out-of-plane intensity of 9.9 +/- 12.6 km mol(-1) arises from the cancellation of large charge contributions by dipolar polarization contributions. The experimental average in-plane C-F bending intensity, 5.8 +/- 7.3 km mol(-1), is also small owing to charge and charge transfer-counterpolarization sums being canceled by their interaction contributions. Models containing only atomic charges and their fluxes are incapable of describing electronic structure changes for simple molecular distortions that are of interest in classifying infrared intensities. One can expect dipolar polarization effects to also be important for larger distortions of chemical interest. (AU)

• FAPESP's process: 16/07411-4 - Assessment, validation and interpretation of the absolute infrared intensities of the vibrational bands of chlorofluoromethanes
• Grantee: Leonardo José Duarte
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 14/21241-9 - The inclusion of polarization effects in the description of amino acids and peptides through the use of atomic multipoles obtained from electron densities
• Grantee: Arnaldo Fernandes da Silva Filho
• Support Opportunities: Scholarships in Brazil - Post-Doctoral