Delocalization and stretch-bend mixing of the HOH bend in liquid water

Carpenter, William B and Fournier, Joseph A and Biswas, Rajib and Voth, Gregory A and Tokmakoff, Andrei (2017) Delocalization and stretch-bend mixing of the HOH bend in liquid water. In: JOURNAL OF CHEMICAL PHYSICS, 147 (8).

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Abstract

Liquid water's rich sub-picosecond vibrational dynamics arise from the interplay of different high and low-frequency modes evolving in a strong yet fluctuating hydrogen bond network. Recent studies of the OH stretching excitations of H2O indicate that they are delocalized over several molecules, raising questions about whether the bending vibrations are similarly delocalized. In this paper, we take advantage of an improved 50 fs time-resolution and broadband infrared (IR) spectroscopy to interrogate the 2D IR lineshape and spectral dynamics of the HOH bending vibration of liquid H2O. Indications of strong bend-stretch coupling are observed in early time 2D IR spectra through a broad excited state absorption that extends from 1500 cm(-1) to beyond 1900 cm(-1), which corresponds to transitions from the bend to the bend overtone and OH stretching band between 3150 and 3550 cm(-1). Pump-probe measurements reveal a fast 180 fs vibrational relaxation time, which results in a hot-ground state spectrum that is the same as observed for water IR excitation at any other frequency. The fastest dynamical time scale is 80 fs for the polarization anisotropy decay, providing evidence for the delocalized or excitonic character of the bend. Normal mode analysis conducted on water clusters extracted from molecular dynamics simulations corroborate significant stretch-bend mixing and indicate delocalization of delta(HOH) on 2-7 water molecules. Published by AIP Publishing.

Item Type:	Journal Article
Publication:	JOURNAL OF CHEMICAL PHYSICS
Additional Information:	Copy right for this article belongs to the AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	30 Sep 2017 09:20
Last Modified:	30 Sep 2017 09:20
URI:	http://eprints.iisc.ac.in/id/eprint/57942

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