High-resolution slice imaging of quantum state-to-state photodissociation of methyl bromide

M.L. Lipciuc, M.H.M. Janssen

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    Abstract

    The photodissociation of rotationally state-selected methyl bromide is studied in the wavelength region between 213 and 235 nm using slice imaging. A hexapole state selector is used to focus a single (JK=11) rotational quantum state of the parent molecule, and a high speed slice imaging detector measures directly the three-dimensional recoil distribution of the methyl fragment. Experiments were performed on both normal (C H3 Br) and deuterated (C D3 Br) parent molecules. The velocity distribution of the methyl fragment shows a rich structure, especially for the C D3 photofragment, assigned to the formation of vibrationally excited methyl fragments in the 1 and 4 vibrational modes. The C H3 fragment formed with ground state Br (P 32 2) is observed to be rotationally more excited, by some 230-340 cm-1, compared to the methyl fragment formed with spin-orbit excited Br (P 12 2). Branching ratios and angular distributions are obtained for various methyl product states and they are observed to vary with photodissociation energy. The nonadiabatic transition probability for the Q 0+ 3 → Q11 transition is calculated from the images and differences between the isotopes are observed. Comparison with previous non-state-selected experiments indicates an enhanced nonadiabatic transition probability for state-selected K=1 methyl bromide parent molecules. From the state-to-state photodissociation experiments the dissociationenergy for both isotopes was determined, D0 (C H3 Br) =23 400±133 cm-1 and D0 (C D3 Br) =23 827±94 cm-1. © 2007 American Institute of Physics.
    Original languageEnglish
    Pages (from-to)224310
    JournalJournal of Chemical Physics
    Volume127
    Issue number22
    DOIs
    Publication statusPublished - 2007

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