%A RA Relph
%A BM Elliott
%A GH Weddle
%A MA Johnson
%A D Jing
%A KD Jordan
%J Journal of Physical Chemistry A
%T Vibrationally induced interconversion of H-bonded NO 2- ? H 2O isomers within NO 2- ? H 2O?Ar m clusters using IR - IR pump - Probe through the OH and NO stretching vibrations
%X We introduce a method based on sequential application of vibrational predissociation spectroscopy to explore the high-amplitude rearrangements available in a small H-bonded complex that is vibrationally excited within a larger Ar cluster. The weakly bound Ar atoms play the role of a solvent in mediating the energy content of the embedded system, ultimately quenching it into local minima through evaporation. We demonstrate the approach on the NO 2-?H 2O binary hydrate, which is known to occur in two nearly isoenergetic isomeric forms. The scheme involves three stages of mass separation to select a particular NO 2-?H 2O?Ar m parent ion cluster prior to vibrational excitation and then isolate the NO 2-?H 2O?Ar fragment ions for interrogation using resonant vibrational predissociation with a second infrared laser. The initial vibrational excitation selectively energizes one of the isomers through one of its characteristic resonances while the predissociation spectrum of the NO 2-?H 2O? Ar fragment encodes the distribution of isomers present after Ar evaporation. Isomerization from the front- to backside form is found to occur upon excitation of the NO stretch near 1200 cm -1; although the reverse reaction is not observed upon excitation of the NO stretch, it is observed upon excitation of the higher-energy OH stretching fundamental near 3000 cm -1. We discuss these observations in the context of the calculated isomerization energetics, which focus on the minimum energy structures for the isomers as well as the transition states for their interconversion. ? 2009 American Chemical Society.
%N 6
%P 975 - 981
%V 113
%D 2009
%R 10.1021/jp808283r
%L pittir16155