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Title: Observation of a remarkable temperature effect in the hydrogen bonding structure and dynamics of the CN-(H2O) cluster

The CN-(H2O) cluster represents a model diatomic monohydrate with multiple solvation sites. We report joint experimental and theoretical studies of its structure and dynamics using temperature-controlled photoelectron spectroscopy (PES) and ab-initio electronic structure calculations. The observed PES spectra of CN-(H2O) display a remarkable temperature effect, namely that the T=12 K spectrum shows an unexpectedly large blue shift of 0.25 eV in the electron binding energy relative to the Room Temperature (RT) spectrum. Extensive theoretical analysis of the potential energy function (PEF) of the cluster at the CCSD(T) level of theory reveal the existence of two nearly isoenergetic isomers corresponding to H2O forming a H-bond with either the C or the N atom, respectively. This results in four topologically distinct minima, i.e., CN-(HaOHb), CN-(HbOHa), NC-(HaOHb) and NC-(HbOHa). There are two main pathways connecting these minima: (i) CN- tumbling relative to water and (ii) water rocking relative to CN-. The relative magnitude of the barriers associated with these two motions reverses between low [pathway (i) is preferred] and high [pathway (ii) is preferred] temperatures. As a result, at T=12 K the cluster adopts a structure that is close to the minimum energy CN-(H2O) configuration, while at RT it can effectively access regionsmore » of the PEF close to the transition state for pathway (ii), explaining the surprisingly large spectral shift between the 12 K and RT PES spectra. This work was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences, US Department of Energy. Battelle operates Pacific Northwest National Laboratory for the US Department of Energy.« less
Authors:
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Publication Date:
OSTI Identifier:
973994
Report Number(s):
PNNL-SA-67173
30794; KC0301020; TRN: US201007%%174
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry A, 113(35):9579-9584; Journal Volume: 113; Journal Issue: 35
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; BINDING ENERGY; BONDING; CONFIGURATION; ELECTRONIC STRUCTURE; ELECTRONS; HYDROGEN; ISOMERS; PHOTOELECTRON SPECTROSCOPY; POTENTIAL ENERGY; SOLVATION; SPECTRA; SPECTRAL SHIFT; TEMPERATURE DEPENDENCE; WATER; http://pubs.acs.org/doi/abs/10.1021/jp9034002; Environmental Molecular Sciences Laboratory