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Conformer specific dissociation dynamics of iodocyclohexane studied by velocity map imaging

Zaouris, DK; Wenge, AM; Murdock, D; Oliver, TAA; Richmond, G; Ritchie, GAD; Dixon, RN; (2011) Conformer specific dissociation dynamics of iodocyclohexane studied by velocity map imaging. The Journal of Chemical Physics , 135 (9) , Article 094312. 10.1063/1.3628682. Green open access

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Abstract

The photodissociation dynamics of iodocyclohexane has been studied using velocity map imaging following excitation at many wavelengths within its A-band (230 ≤ λ ≤ 305 nm). This molecule exists in two conformations (axial and equatorial), and one aim of the present experiment was to explore the extent to which conformer-specific fragmentation dynamics could be distinguished. Ground (I) and spin-orbit excited (I*) state iodine atom products were monitored by 2 + 1 resonance enhanced multiphoton ionization, and total kinetic energy release (TKER) spectra and angular distributions derived from analysis of images recorded at all wavelengths studied. TKER spectra obtained at the longer excitation wavelengths show two distinct components, which can be attributed to the two conformers and the different ways in which these partition the excess energy upon C–I bond fission. Companion calculations based on a simple impulsive model suggest that dissociation of the equatorial (axial) conformer preferentially yields vibrationally (rotationally) excited cyclohexyl co-fragments. Both I and I* products are detected at the longest parent absorption wavelength (λ ∼ 305 nm), and both sets of products show recoil anisotropy parameters, β > 1, implying prompt dissociation following excitation via a transition whose dipole moment is aligned parallel to the C–I bond. The quantum yield for forming I* products, ΦI*, has been determined by time resolved infrared diode laser absorption methods to be 0.14 ± 0.02 (at λ = 248 nm) and 0.22 ± 0.05 (at λ = 266 nm). Electronic structure calculations indicate that the bulk of the A-band absorption is associated with transition to the 4A ′ state, and that the (majority) I atom products arise via non-adiabatic transfer from the 4A ′ potential energy surface (PES) via conical intersection(s) with one or more PESs correlating with ground state products.

Type: Article
Title: Conformer specific dissociation dynamics of iodocyclohexane studied by velocity map imaging
Open access status: An open access version is available from UCL Discovery
DOI: 10.1063/1.3628682
Publisher version: http://dx.doi.org/10.1063/1.3628682
Language: English
Additional information: Reprinted with permission from Zaouris, DK; Wenge, AM; Murdock, D; Oliver, TAA; Richmond, G; Ritchie, GAD; Dixon, RN; (2011) Conformer specific dissociation dynamics of iodocyclohexane studied by velocity map imaging. The Journal of Chemical Physics, 135 (9), Article 094312. 10.1063/1.3628682. Copyright 2011, American Institute of Physics.
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1475104
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