Wigner Near-Threshold Effects in the Photoelectron Angular Distribution of NO 2 -

B. A. Laws*, S. J. Cavanagh, B. R. Lewis, S. T. Gibson

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    5 Citations (Scopus)


    High-resolution velocity map imaged photoelectron spectra of the nitrite anion NO2- are measured over a range of photodetachment wavelengths between 355 and 550 nm, resolving the vibrational and rotational structure of the NO2(X2A1) + e- ← NO2-(X1A1) + hν transition. A full rotational band model is constructed to define the spectroscopic constants of both the neutral and the lesser studied anion ground states. The corresponding photoelectron angular distributions are characterized by a large positive anisotropy parameter, with β ≈ 1.5 gradually increasing to β ≈ 1.7 upon approaching the threshold. However, at very low kinetic energies, within 0.1 eV of the threshold, β dramatically drops to 0. This behavior is a consequence of the Wigner near-threshold selectivity of the electron partial-wave cross sections, whereby an atomic p-like orbital character adjacent to the threshold is favored. The full kinetic energy dependence of β is reproduced by a new mixed spd orbital model, yielding a NO2-(X1A1) molecular-orbital decomposition of 2% p, 44% s, and 54% d character.

    Original languageEnglish
    Pages (from-to)10418-10425
    Number of pages8
    JournalJournal of Physical Chemistry A
    Issue number48
    Publication statusPublished - 5 Dec 2019


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