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The workings of a molecular thermometer: the vibrational excitation of carbon tetrachloride by a solvent

Graham, Polly B., Matus, Kira J. M. and Stratt, Richard M. (2004) The workings of a molecular thermometer: the vibrational excitation of carbon tetrachloride by a solvent. Journal of Chemical Physics, 121 (11). pp. 5348-5355. ISSN 0021-9606

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Identification Number: 10.1063/1.1784441


An intriguing energy-transfer experiment was recently carried out in methanol/carbon tetrachloride solutions. It turned out to be possible to watch vibrational energy accumulating in three of carbon tetrachloride’s modes following initial excitation of O-H and C-H stretches in methanol, in effect making those CCl4 modes “molecular thermometers” reporting on methanol’s relaxation. In this paper, we use the example of a CCl4 molecule dissolved in liquid argon to examine, on a microscopic level, just how this kind of thermal activation occurs in liquid solutions. The fact that even the lowest CCl4 mode has a relatively high frequency compared to the intermolecular vibrational band of the solvent means that the only solute-solvent dynamics relevant to the vibrational energy transfer will be extraordinarily local, so much so that it is only the force between the instantaneously most prominent Cl and solvent atoms that will significantly contribute to the vibrational friction. We use this observation, within the context of a classical instantaneous-pair Landau-Teller calculation, to show that energy flows into CCl4 primarily via one component of the nominally degenerate, lowest frequency, E mode and does so fast enough to make CCl4 an excellent choice for monitoring methanol relaxation. Remarkably, within this theory, the different symmetries and appearances of the different CCl4 modes have little bearing on how well they take up energy from their surroundings—it is only how high their vibrational frequencies are relative to the solvent intermolecular vibrational band edge that substantially favors one mode over another

Item Type: Article
Official URL:
Additional Information: © 2004 American Institute of Physics
Divisions: Government
Centre for Analysis of Risk & Regulation
Subjects: Q Science > QD Chemistry
Date Deposited: 24 Feb 2011 16:17
Last Modified: 16 May 2024 00:16

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