Vibronic coupling in the superoxide anion
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Subtitle: The vibrational dependence of the photoelectron angular distribution
Author list: Mbaiwa, Foster
Publisher: AIP Publishing
Publication year: 2010
Journal: The Journal of Chemical Physics (0021-9606)
Volume number: 133
Issue number: 17
ISSN: 0021-9606
eISSN: 1089-7690
Languages: English-United States (EN-US)
Abstract
We present a comprehensive photoelectron imaging study of theO 2(X2∑g, v′ =0-6) ←O 2
- (X2Πg, v″ =0) and O 2 (a 1Δg, v′=0-4)←O 2
-((X2Πg, v″ =0) photodetachment bands at wavelengths between 900 and 455 nm, examining the effect of vibronic coupling on the photoelectron angular distribution (PAD). This work extends the v′ =1-4 data for detachment into the ground electronic state, presented in a recent communication [R. Mabbs, F. Mbaiwa, J. Wei, M. Van Duzor, S. T. Gibson, S. J. Cavanagh, and B. R. Lewis, Phys. Rev. A 82, 011401(R) (2010)]. Measured vibronic intensities are compared to Franck-Condon predictions and used as supporting evidence of vibronic coupling. The results are analyzed within the context of the one-electron, zero core contribution (ZCC) model [R. M. Stehman and S. B. Woo, Phys. Rev. A 23, 2866 (1981)]. For both bands, the photoelectron anisotropy parameter variation with electron kinetic energy, β (E), displays the characteristics of photodetachment from a d -like orbital, consistent with the πg 2p highest occupied molecular orbital ofO2
-. However, differences exist between the β trends for detachment into different vibrational levels of the X 2∑g and a 1Δg electronic states ofO2
-. The ZCC model invokes vibrational channel specific "detachment orbitals" and attributes this behavior to coupling of the electronic and nuclear motion in the parent anion. The spatial extent of the model detachment orbital is dependent on the final state of O2: the higher the neutral vibrational excitation, the larger the electron binding energy. Although vibronic coupling is ignored in most theoretical treatments of PADs in the direct photodetachment of molecular anions, the present findings clearly show that it can be important. These results represent a benchmark data set for a relatively simple system, upon which to base rigorous tests of more sophisticated models.
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