Vector correlations in the 157 nm photodissociation of OCS and the 266 nm photodissociation of methyl iodide

Rachel Ogorzalek Loo, Charles E. Strauss, Hans Peter Haerri, Gregory E. Hall, Paul L. Houston*, Itamar Burak, John W. Hepburn

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

The photodissociations of OCS at 157 nm and of CH3I(CD3I) at 266 nm have been investigated by using tunable vacuum ultraviolet laser-induced fluorescence and multiphoton ionization to probe the CO or S and the CH3(CD3) or I photoproducts, respectively. In the OCS dissociation, sulphur is produced almost entirely in the S(1S) state, while CO is produced in its ground electronic state and in vibrational levels v = 0-3 in the approximate ratio (v = 0): (v = 1): (v = 2): (v = 3) = (1.0): (1.0): (0.5): (0.3). The rotational distribution for each vibrational level is found to be near-Boltzmann, with temperatures that decrease from 1350 K for v = 0 to 770 K for v = 3. Measurements of the CO Doppler profiles demonstrate that the dissociation takes place from a transition of predominantly parallel character (β > 1.3) and that the CO velocity and angular momentum vectors are perpendicular to one another. In the CD3I dissociation, the ratio of CD3 (v = 0)/(v = 2) was estimated to be ca. 1.1, with multiple determinations in the range 0.47-2.1. The quantum number v here denotes the nascent excitation of the v2 'umbrella' mode. A value for the CH3(v = 0)/(v = 2) ratio from dissociation of CH3l could not be estimated, although it was clearly larger than that for CD3. The CH3 (v = 0) and CD3 (v = 0) products from this dissociation are fitted by 120 ± 30 K and 105 ± 30 K rotational distributions, respectively. The dissociation mechanism produces alignment in the molecular frame such that there is a strong preference for low values of K. Assuming that the relative velocity vector lies along the CH3 C3 axis, then the velocity and rotation vectors tend to be perpendicular.

Original languageEnglish
Pages (from-to)1185-1205
Number of pages21
JournalJournal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics
Volume85
Issue number8
DOIs
StatePublished - 1989

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