Relph, RA and Elliott, BM and Weddle, GH and Johnson, MA and Jing, D and Jordan, KD
(2009)
Vibrationally induced interconversion of H-bonded NO <inf>2</inf><sup>-</sup> · H <inf>2</inf>O isomers within NO <inf>2</inf><sup>-</sup> · H <inf>2</inf>O·Ar <inf>m</inf> clusters using IR - IR pump - Probe through the OH and NO stretching vibrations.
Journal of Physical Chemistry A, 113 (6).
975 - 981.
ISSN 1089-5639
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Abstract
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.
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