Photodetachment of O− yielding o(1D2, 3P) atoms, viewed with velocity map imaging

Abstract

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.35]{O-fig.eps} \end{wrapfigure} Electron photodetachment of O$^-$($^{2}P_{3/2,1/2}$) is measured using velocity-map imaging at wavelengths near 350~nm, where detachment yields both O($^1\!D_2$) and O($^3P_{2,1,0}$) atoms, simultaneously, producing slow ($\sim 0.1$~eV) and fast electrons ($\sim 2$~eV). The photoelectron spectrum resolves the fine-structure transitions, which together with the well known atomic fine-structure splittings,\footnote{physics.nist.gov/cgi-bin/ASD/energy1.pl} and intensity ratios,\footnote{O. Scharf and M. R. Godefried, arXiv:0808.3529v1} provide an excellent test of the spectral quality of the velocity-map imaging technique.

Although the photoelectron angular distribution for the two atomic limits have the same negative anisotropy sign, the energy dependence differs. The variation is qualitatively in accordance with $R$-matrix cross section calculations, that indicate a more gradual $d$-wave onset for the $^1\!D$ limit.\footnote{O. Zatsarinny and K. Bartschat, \emph{Phys. Rev. A}, \textbf{73}, 022714 (2006). doi:10.1103/PhysRevA.73.022714} However, more exact evaluation is only possible with information about the matrix element phases.