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Infrared Spectra of Dimethylphenanthrenes in the Gas phase

Das, Prasanta and Arunan, E and Das, Puspendu K (2012) Infrared Spectra of Dimethylphenanthrenes in the Gas phase. In: JOURNAL OF PHYSICAL CHEMISTRY A, 116 (24, SI). pp. 5769-5778.

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Official URL: http://dx.doi.org/10.1021/jp2045542


Infrared spectra of atmospherically and astronomically important dimethylphenanthrenes (DMPs), namely 1,9-DMP, 2,4-DMP, and 3,9-DMP, were recorded in the gas phase from 400 to 4000 cm(-1) with a resolution of 0.5 cm(-1) at 110 degrees C using a 7.2 m gas cell. DFT calculations at the B3LYP/6-311G** level were carried out to get the harmonic and anharmonic frequencies and their corresponding intensities for the assignment of the observed bands. However, spectral assignments could not be made unambiguously using anharmonic or selectively scaled harmonic frequencies. Therefore, the scaled quantum mechanical (SQM) force field analysis method was adopted to achieve more accurate assignments. In this method force fields instead of frequencies were scaled. The Cartesian force field matrix obtained from the Gaussian calculations was converted to a nonredundant local coordinate force field matrix and then the force fields were scaled to match experimental frequencies in a consistent manner using a modified version of the UMAT program of the QCPE package. Potential energy distributions (PEDs) of the normal modes in terms of nonredundant local coordinates obtained from these calculations helped us derive the nature of the vibration at each frequency. The intensity of observed bands in the experimental spectra was calculated using estimated vapor pressures of the DMPs. An error analysis of the mean deviation between experimental and calculated intensities reveal that the observed methyl C-H stretching intensity deviates more compared to the aromatic C-H and non C-H stretching bands.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to American Chemical Society
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Depositing User: Francis Jayakanth
Date Deposited: 16 Jul 2012 11:15
Last Modified: 05 Mar 2019 06:39
URI: http://eprints.iisc.ac.in/id/eprint/44848

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