Study of the upper spin–orbit state of the chloroiodomethane cation by mass-analyzed threshold ionization

The vibrational spectrum of CH2ClI+ in the upper spin–orbit state was obtained by one-photon mass-analyzed threshold ionization (MATI) spectrometry. The accurate ionization energy of the upper spin–orbit state was determined to be 10.3045 ± 0.0006 eV. The energy gap between the upper and lower spin–orbit states was 0.5539 ± 0.0012 eV. The frequency of the Cl–C–I bending mode was found to be most affected by the spin–orbit interaction. This suggests that the avoided crossing between the lower and upper spin–orbit states occurs along a direction close to the Cl–C–I bending coordinate.