title: Photodissociation dynamics of the iodide-uracil (I(-)U) complex.
abstract: 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 I(-)U, 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.
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Wei-Li
authors.initials: WL
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Alice
authors.initials: A
authors.lastname: Kunin
authors.affiliation: Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.
authors.forename: Edward
authors.initials: E
authors.lastname: Matthews
authors.affiliation: Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.
authors.forename: Naruo
authors.initials: N
authors.lastname: Yoshikawa
authors.affiliation: Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom.
authors.forename: Caroline E H
authors.initials: CE
authors.lastname: Dessent
authors.affiliation: Department of Chemistry, University of California, Berkeley, California 94720, USA.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Neumark