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 Title: VARIABLE MIXED ORBITAL CHARACTER IN THE PHOTOELECTRON ANGULAR DISTRIBUTION OF NO2 Author(s): Laws, Benjamin A Contributor(s): Gibson, Stephen T; Lewis, Brenton R; Cavanagh, Steven J Subject(s): Mini-symposium: Multiple Potential Energy Surfaces Abstract: begin{wrapfigure}{r}{0pt}_x000d_ includegraphics[scale=0.3]{no2470nm3.eps}_x000d_ end{wrapfigure}_x000d_ _x000d_ NO$_{2}$ a key component of photochemical smog and an important species in the Earth's atmosphere, is an example of a molecule which exhibits significant mixed orbital character in the HOMO. In photoelectron experiments the geometric properties of the parent anion orbital are reflected in the photoelectron angular distribution (PAD), an area of research that has benefited largely from the ability of velocity-map imaging (VMI) to simultaneously record both the energetic and angular information, with 100% collection efficiency. _x000d_ _x000d_ Photoelectron spectra of NO$_{2}^{-}$, taken over a range of wavelengths (355nm-520nm) with the ANU's VMI spectrometer, reveal an anomalous jump in the anisotropy parameter near threshold. Consequently, the orbital behavior of NO$_{2}^{-}$ appears to be quite different near threshold compared to detachment at higher photon energies. This surprising effect is due to the Wigner Threshold law, which causes $p$ orbital character to dominate the photodetachment cross-section near threshold, before the mixed $s/d$ orbital character becomes significant at higher electron kinetic energies.footnote{K. J. Reed, A. H. Zimmerman, H. C. Andersen, and J. I. Brauman, emph{J. Chem. Phys.} {bf 64}, 1368, (1976). doi:10.1063/1.432404} _x000d_ _x000d_ By extending recent work on binary character modelsfootnote{D. Khuseynov, C. C. Blackstone, L. M. Culberson, and A. Sanov, emph{J. Chem. Phys.} {bf 141}, 124312, (2014). doi:10.1063/1.4896241} to form a more general expression, the variable mixed orbital character of NO$_{2}^{-}$ is able to be described. This study provides the first multi-wavelength NO$_{2}$ anisotropy data, which is shown to be in decent agreement with much earlier zero-core model predictionsfootnote{W. B. Clodius, R. M. Stehman, and S. B. Woo, emph{Phys. Rev. A.} {bf 28}, 760, (1983). doi:10.1103/PhysRevA.28.760} of the anisotropy parameter.letthefootnoterelaxfootnotetext{Research supported by the Australian Research Council Discovery Project Grant DP160102585} Issue Date: 6/20/2017 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/96857 DOI: 10.15278/isms.2017.TB07 Date Available in IDEALS: 2017-07-27
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