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Issue 44, 2015
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Anharmonicities and coherent vibrational dynamics of phosphate ions in bulk H2O

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Abstract

Phosphates feature prominently in the energetics of metabolism and are important solvation sites of DNA and phospholipids. Here we investigate the ion H2PO4 in aqueous solution combining 2D IR spectroscopy of phosphate stretching vibrations in the range from 900–1300 cm−1 with ab initio calculations and hybrid quantum-classical molecular dynamics based simulations of the non-linear signal. While the line shapes of diagonal peaks reveal ultrafast frequency fluctuations on a sub-100 fs timescale caused by the fluctuating hydration shell, an analysis of the diagonal and cross-peak frequency positions allows for extracting inter-mode couplings and anharmonicities of 5–10 cm−1. The excitation with spectrally broad pulses generates a coherent superposition of symmetric and asymmetric PO2 stretching modes resulting in the observation of a quantum beat in aqueous solution. We follow its time evolution through the time-dependent amplitude and the shape of the cross peaks. The results provide a complete characterization of the H2PO4 vibrational Hamiltonian including fluctuations induced by the native water environment.

Graphical abstract: Anharmonicities and coherent vibrational dynamics of phosphate ions in bulk H2O

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Supplementary files

Article information


Submitted
30 Jul 2015
Accepted
30 Sep 2015
First published
01 Oct 2015

Phys. Chem. Chem. Phys., 2015,17, 29906-29917
Article type
Paper
Author version available

Anharmonicities and coherent vibrational dynamics of phosphate ions in bulk H2O

R. Costard, T. Tyborski and B. P. Fingerhut, Phys. Chem. Chem. Phys., 2015, 17, 29906
DOI: 10.1039/C5CP04502A

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