Study of photoionization mass spectrum of carbon monoxide from ionization threshold to 575 Å by using synchrotron radiation

Highlights: • Photoionization thresholds were determined for the X²Σ⁺, A²Π and B²Σ⁺ states of CO⁺. • Some Rydberg series are extended to higher number. • Some new members are classified for the first time. The vacuum-ultraviolet photoionization efficiency spectroscopy (PIES) of carbon monoxide in a region 575–890 Å has been investigated with time-of-flight (TOF) photoionization mass spectrometry (PIMS) by using tunable synchrotron radiation (SR). Three photoionization thresholds were determined to be 14.015, 16.550 eV and 19.670 eV for the X²Σ⁺, A²Π and B²Σ⁺ states of CO⁺, respectively, which are in very good agreement with those of previous investigation. Furthermore, the Rydberg series converging to the X²Σ⁺, A²Π, B²Σ⁺, D²Π and C²Σ⁺ states of CO⁺ were assigned clearly, according to the PIES of CO and calculation with Rydberg series formula. In particular, the Rydberg series (R_X-I) (ν⁺ = 2, 3 and 4) and R_X-TTI series (ν⁺ = 1, 2, 3 and 4) converging to CO⁺ (X²Σ⁺), the Rydberg series (R_B-V) (ν⁺ = 1, 2 and 3) converging to CO⁺ (B²Σ⁺), and a new vibrational progression (n = 2) converging to CO⁺ (A²Π) were all identified and listed for the first time. Generally speaking, the Rydberg series identified in this work are in good accordance with those of previous study. Moreover, some of them are extended to higher number, and some new members are classified for the first time.