A high resolution pulsed field ionization photoelectron study of O2 using third generation undulator synchrotron radiation

We have improved a newly developed experimental scheme for high resolution pulsed field ionization photoelectron (PFI-PE) studies [Hsu et al., Rev. Sci. Instrum. (in press)] using the high resolution monochromatized multibunch undulator synchrotron source of the Chemical Dynamics Beamline at the Advanced Light Source. This improved scheme makes possible PFI-PE measurements with essentially no contamination by background electrons arising from direct photoionization and prompt autoionization processes. We present here a preliminary analysis of the rotationally resolved PFI-PE spectrum for ${\mathrm{O}}_{\mathrm{2}}$ obtained at a resolution of 0.5 meV (full-width-at-half-maximum) in the photon energy range of 18.1–19.4 eV, yielding accurate ionization energies for the transitions ${\mathrm{O}}_2^{+}{\mathrm{(b\hspace{0.17em}}}^4{\Sigma }_g^{-}{\mathrm{,\hspace{0.5em}v}}^{+}{\text{=0–9,\hspace{0.5em}N}}^{+}\text{=1)←}{\mathrm{O}}_2{\mathrm{(X\hspace{0.17em}}}^3{\Sigma }_g^{-}\text{,\hspace{0.5em}v=0,}$ $\text{N=1).}$