Photodissociation dynamics of the iodide-uracil (I-U) complex

Wei Li Li, Alice Kunin, Edward Matthews, Naruo Yoshikawa, Caroline E.H. Dessent, Daniel M. Neumark

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Photofragment action spectroscopy and femtosecond time-resolved photoelectron imaging are utilized to probe the dissociation channels in iodide-uracil (I ⋅ U) binary clusters upon photoexcitation. The photofragment action spectra show strong I and weak [U- H] ion signal upon photoexcitation. The action spectra show two bands for I and [U- H] production peaking around 4.0 and 4.8 eV. Time-resolved experiments measured the rate of I production resulting from excitation of the two bands. At 4.03 eV and 4.72 eV, the photoelectron signal from I exhibits rise times of 86 ± 7 ps and 36 ± 3 ps, respectively. Electronic structure calculations indicate that the lower energy band, which encompasses the vertical detachment energy (4.11 eV) of IU, corresponds to excitation of a dipole-bound state of the complex, while the higher energy band is primarily a π-π excitation on the uracil moiety. Although the nature of the two excited states is very different, the long lifetimes for I production suggest that this channel results from internal conversion to the I ⋅ U ground state followed by evaporation of I. This hypothesis was tested by comparing the dissociation rates to Rice-Ramsperger-Kassel-Marcus calculations.

Original languageEnglish
Article number044319
Number of pages8
JournalJournal of Chemical Physics
Issue number4
Early online date29 Jul 2016
Publication statusE-pub ahead of print - 29 Jul 2016

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  • Radiation Chemistry
  • Laser Spectroscopy
  • Electron-DNA interactions
  • Nucleobase

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