Infrared–vacuum ultraviolet–pulsed field ionization–photoelectron study of $CH3I+$ using a high-resolution infrared laser Available to Purchase

By using a high-resolution single mode infrared-optical parametric oscillator laser to prepare $CH3I$ in single $(J,K)$ rotational levels of the $ν1$ (symmetric C–H stretching) $=1$ vibrational state, we have obtained rovibrationally resolved infrared–vacuum ultraviolet–pulsed field ionization–photoelectron (IR-VUV-PFI-PE) spectra of the $CH3I+(X̃E3∕22;ν1+=1;J+,P+)$ band, where $(J,K)$ and $(J+,P+)$ represent the respective rotational quantum numbers of $CH3I$ and $CH3I+$⁠. The IR-VUV-PFI-PE spectra observed for $K=0$ and 1 are found to have nearly identical structures. The IR-VUV-PFI-PE spectra for $(J,K)=(5,0)$ and (7, 0) are also consistent with the previous $J$-selected IR-VUV-PFI-PE measurements. The analysis of these spectra indicates that the photoionization cross section of $CH3I$ depends strongly on $∣ΔJ+∣=∣J+−J∣$ but not on $J$ and $K$⁠. This observation lends strong support for the major assumption adopted for the semiempirical simulation scheme, which has been used for the simulation of the origin bands observed in VUV-PFI-PE study of polyatomic molecules. Using the state-to-state photoionization cross sections determined in this IR-VUV study, we have obtained excellent simulation of the VUV-PFI-PE origin band of $CH3I+(X̃E3∕22)$⁠, yielding more precise $IE(CH3I)=76930.7±0.5cm−1$ and $ν1+=2937.8±0.2cm−1$⁠.