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Infrared Spectra of Dimethylquinolines in the Gas Phase: Experiment and Theory

Das, Prasanta and Manogaran, S and Arunan, E and Das, Puspendu K (2010) Infrared Spectra of Dimethylquinolines in the Gas Phase: Experiment and Theory. In: Journal of Physical Chemistry A, 114 (32). pp. 8351-8358.

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Official URL: http://pubs.acs.org/doi/abs/10.1021/jp1056896


Infrared spectra of atmospherically important dimethylquinolines (DMQs), namely 2,4-DMQ, 2,6-DMQ, 2,7-DMQ, and 2,8-DMQ in the gas phase at 80 degrees C were recorded using a long variable path-length cell. DFT calculations were carried out to assign the bands in the experimentally observed spectra at the B3LYP/6-31G* level of theory. The spectral assignments particularly for the C-H stretching modes could not be made unambiguously using calculated anharmonic or scaled harmonic frequencies. To resolve this problem, a scaled force field method of assignment was used. Assignment of fundamental modes was confirmed by potential energy distributions (PEDs) of the normal modes derived by the scaled force fields using a modified version of the UMAT program in the QCPE package. We demonstrate that for large molecules such as the DMQs, the scaling of the force field is more effective in arriving at the correct assignment of the fundamentals for a quantitative vibrational analysis. An error analysis of the mean deviation of the calculated harmonic, anharmonic, and force field fitted frequencies from the observed frequency provides strong evidence for the correctness of the assignment.

Item Type: Journal Article
Publication: Journal of Physical Chemistry A
Publisher: American Chemical Society
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 06 Sep 2010 11:10
Last Modified: 19 Sep 2010 06:15
URI: http://eprints.iisc.ac.in/id/eprint/31976

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