Rovibrational-state-selected pulsed field ionization-photoelectron study of methyl iodide using two-color infrared-vacuum ultraviolet lasers.

The preparation of methyl iodide (CH₃I) in selected rovibrational states [ν₇=1 (C-H stretch); J] by infrared (IR) excitation prior to vacuum ultraviolet (VUV) photoionization has greatly simplified the observed pulsed field ionization-photoelectron (PFI-PE) spectra, allowing the direct determination of the rotational constants B⁺(C⁺)=0.254±0.003 cm^-1 for CH₃I⁺(X ²E_3/2;ν₇⁺) and the ionization energy (76 896.9±0.2 cm-1) for CH₃I⁺(X ²E_3/2;ν₇⁺=1,J⁺=3/2)←CH₃I(X ¹A₁;ν₇=1,J=0). The IR-VUV-PFI-PE and IR-VUV-photoion measurements also provide relative state-to-state (ν₇⁺=1, J⁺←ν₇=1, J) cross sections for the photoionization process. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]