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Issue 2, 2003
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High resolution ion imaging studies of the photodissociation of the Br2+ cation

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We demonstrate the potential of velocity map ion imaging methods for high resolution studies of the photofragmentation of a state selected molecular ion, Br2+. 79Br2+ cations were prepared in the v+ = 1 levels of both spin–orbit components of the X 2Πg ground state by 2 + 1 resonance enhanced multiphoton ionisation (REMPI) of jet-cooled, isotopomer-selected 79Br2 molecules at an excitation wavelength of 263.012 nm. The subsequent photolysis of these state selected ions was then investigated in the wavelength range 372 < λphot < 432 nm by imaging the resulting 79Br+ ions. Use of a home-built Pockels cell assembly allowed measurement of images with and without λphot present, on successive laser shots. The resulting difference image allows clear visualisation of the parent ion fragmentation, free from unintended fragment ion signal induced by the REMPI preparation step. The images reveal participation of dissociation channels yielding Br+ ions in both their ground (3P2) and first excited (3P1) spin–orbit states, together with ground state Br atoms. No fragmentation channels involving formation of spin–orbit excited Br(2P1/2) atoms are found to be active in this range of photolysis wavelengths. Image analysis yields a precise value for the bond strength of the Br2+ cation, in both spin–orbit components of its ground electronic state: D0[79Br2+(X 2Π1/2,g)] = 23528.1 ± 0.6 cm−1 and D0[79Br2+(X 2Π3/2,g)] = 26345 ± 2 cm−1, and thus a refined measure of the spin–orbit splitting in the ground state Br2+ cation: A = 2817 ± 3 cm−1.

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Publication details

The article was received on 23 Sep 2002, accepted on 21 Nov 2002 and first published on 06 Dec 2002

Article type: Paper
DOI: 10.1039/B209310N
Citation: Phys. Chem. Chem. Phys., 2003,5, 308-314
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    High resolution ion imaging studies of the photodissociation of the Br2+ cation

    M. Beckert, S. J. Greaves and M. N. R. Ashfold, Phys. Chem. Chem. Phys., 2003, 5, 308
    DOI: 10.1039/B209310N

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