Autoionization observed in the CO+ (A 2Π–X 2Σ+) and (B 2Σ+–X 2Σ+) fluorescence excitation spectra

Abstract

The CO⁺ (A ²Π–X ²Σ⁺) and (B ²Σ⁺–X ²Σ⁺) fluorescence excitation spectra (FES) using VUV synchrotron radiation, have been measured from 16 to 38 eV excitation energy. Total photoionization cross section has also been measured from 17 to 20 eV for comparison. Sharp ionization onsets typical of direct ionization process are observed for both A ²Π and B ²Σ⁺ thresholds. New autoionization structures have been observed above 20 eV besides the broad shape resonance located at 32 eV in the (B–X) FES. Sharp structures observed above the A ²Π (v=0) threshold are interpreted in terms of electronically induced vibrational autoionization. Branching ratios for electronic autoionization of four Ryberg series converging to B into the CO⁺ A and X states have been measured. Those states decay preferentially into the CO⁺ A ²Π state as opposed to X ²Σ⁺.