Piskulich ZA, Thompson WH. Temperature Dependence of the Water Infrared Spectrum: Driving Forces, Isosbestic Points, and Predictions.
J Phys Chem Lett 2020;
11:7762-7768. [PMID:
32852956 DOI:
10.1021/acs.jpclett.0c02301]
[Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The temperature derivative of the infrared (IR) spectrum of HOD/D2O is directly calculated from simulations at a single temperature using a fluctuation theory approach. It is demonstrated, on the basis of an energetic decomposition of the derivative, that the blue shift with increasing temperature is associated with the competition between electrostatic and Lennard-Jones interactions. The same competition gives rise, where their contributions cancel, to a near isosbestic point. The derivative is further used to define an effective internal energy (and entropy) associated with the IR spectrum, and it is shown how a van't Hoff relation can be used to accurately predict the spectrum over a wide range of temperatures. These predictions also explain why a precise isosbestic point is not observed.
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