Photodissociation of (SO2) m (H2 O)n clusters employing femtosecond pump-probe spectroscopy

K. L. Knappenberger, A. W. Castleman

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A femtosecond pump-probe technique was employed to study the photodissociation dynamics of (SO2) m (H2 O)n clusters in real time for clusters, where m=1, 2 and n as large as 11. The pump (excitation) step occurs through a multiphoton process which populates the dissociative E state as well as a lower-lying bound state of the sulfur dioxide (SO2) chromosphore. Dissociation of the SO2 monomer occurs through the E state and the decay is fit to a lifetime of 230 fs. The present study is in agreement with our previous investigations of homogeneous (SO2) m clusters that have shown that cluster formation inhibits the dissociation process owing to a steric effect induced by the cluster environment [K. L. Knappenberger, Jr. and A. W. Castleman, Jr., J. Chem. Phys. 121, 3540 (2004)]. The E state lifetime increases sequentially as a function of cluster size to as much as 668 fs when 11 water molecules solvate the chromophore. We have employed a method to compare the ratio of amplitude coefficients, which reflect a respective component of the mathematical fit, to determine the nature of the wave packet evolution in binary clusters. An increase of this ratio by as much as 440% was observed for large cluster sizes. A preferential ion state charge transfer, rather than dissociation, was observed in binary clusters. The significance of cluster size on evaporation processes has been investigated.

Original languageEnglish (US)
Article number154306
JournalJournal of Chemical Physics
Issue number15
StatePublished - Apr 15 2005

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry


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