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Evidence of Polaron Excitations in Low Temperature Raman Spectra of Oxalic Acid Dihydrate

Mohaček Grošev, Vlasta; Grdadolnik, Jože; Hadži, Dušan (2016) Evidence of Polaron Excitations in Low Temperature Raman Spectra of Oxalic Acid Dihydrate. Journal of Physical Chemistry A, 120 (18). pp. 2789-2796. ISSN 1089-5639

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Abstract

Low temperature Raman spectra of oxalic acid dihydrate (8K - 300 K) both for polycrystalline and single crystal phase show strong variation with temperature in the interval from 1200 to 2000 cm-1. Previous low temperature diffraction studies all confirmed the stability of the crystal P21/n phase with no indications of any phase transition, reporting the existence of a strong hydrogen bond between the oxalic acid and a water molecule. A new group of Raman bands in the 1200 – 1300 cm-1 interval below 90 K is observed, caused by possible loss of the centre of inversion. This in turn could originate either due to disorder in hydroxyl proton positions, or due to proton transfer from carboxylic group to water molecule. The hypothesis of proton transfer is further supported by the emergence of new bands centered at 1600 cm-1 and 1813 cm-1, which can be explained with vibrations of H3O+ ions. The broad band at 1600 cm-1 looses intensity, while the band at 1813 cm-1 gains intensity on cooling. The agreement between quantum calculations of vibrational spectra and experimentally observed Raman bands of hydronium ions in oxalic acid sesquihydrate crystal corroborate this hypothesis.

Item Type: Article
Uncontrolled Keywords: oxalic acid dihydrate; polarons; Raman spectroscopy; phonons; oxalic acid sesqui hydrate; low temperature; DFT; lattice dynamics; normal modes
Subjects: NATURAL SCIENCES > Physics > Atomic and Molecular Physics
NATURAL SCIENCES > Physics > Condensed Matter Physics
NATURAL SCIENCES > Chemistry > Physical Chemistry
Divisions: Division of Materials Physics
Depositing User: Vlasta Mohaček Grošev
Date Deposited: 02 Dec 2016 15:46
Last Modified: 19 Apr 2017 23:15
URI: http://fulir.irb.hr/id/eprint/3074
DOI: 10.1021/acs.jpca.5b12577

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