title: Photochemistry of HgBr(2) in methanol investigated using time-resolved X-ray liquidography.
abstract: We investigate the photoinduced dissociation of HgBr(2) in methanol and the ensuring structural dynamics of the photo-products over a time span from 100 ps to 1 μs after photolysis at 267 nm by using time-resolved X-ray liquidography (TRXL). By making use of the atomic-level structural sensitivity of X-ray scattering and the superb 100 ps time resolution of X-ray pulses from a 3rd-generation synchrotron, the structural dynamics of a chemical reaction in solution can be directly monitored. The measured time-dependent X-ray solution scattering signals, analyzed using global-fitting based on DFT calculations and MD simulations, show that photoexcited HgBr(2) dissociates via both two-body (HgBr + Br) and three-body (Hg + Br + Br) dissociation pathways with a ∼2 : 1 branching ratio. Following dissociation, the photoproducts recombine via three reactions involving Br species: (1) Hg + Br, (2) HgBr + Br, and (3) Br + Br. The associated rate constants and branching ratios are determined from the global-fitting analysis. Also, we examine the energy dissipation from reacting solute molecules and relaxation of excited molecules to solvent bath accompanying the temperature rise of 0.54 K. Compared to a previous TRXL study of the photodissociation of HgI(2), the results of this work suggest that the photodissociation pathway of HgBr(2) is different from that of HgI(2), which dissociates predominantly via two-body dissociation, at least to within the currently available time resolution of ∼100 ps. In addition, the error analysis of the fit parameters used in the global-fitting are discussed in detail with a comparison of various error estimation algorithms.
authors.affiliation: Center for Time-Resolved Diffraction, Department of Chemistry, Graduate School of Nanoscience & Technology (WCU), KAIST, Daejeon, 305-701, Republic of Korea.
authors.forename: Sunhong
authors.initials: S
authors.lastname: Jun
authors.forename: Jae Hyuk
authors.initials: JH
authors.lastname: Lee
authors.forename: Jeongho
authors.initials: J
authors.lastname: Kim
authors.forename: Joonghan
authors.initials: J
authors.lastname: Kim
authors.forename: Kyung Hwan
authors.initials: KH
authors.lastname: Kim
authors.forename: Qingyu
authors.initials: Q
authors.lastname: Kong
authors.forename: Tae Kyu
authors.initials: TK
authors.lastname: Kim
authors.forename: Manuela
authors.initials: M
authors.lastname: Lo Russo
authors.forename: Michael
authors.initials: M
authors.lastname: Wulff
authors.forename: Hyotcherl
authors.initials: H
authors.lastname: Ihee