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. (c) 2006 Elsevier B.V. All rights reserved.