ADIABATIC IONIZATION-ENERGY OF CH3SSCH3

The ionization energy (IE) for CH3SSCH3 has been measured by the pulse d molecular beam photoionization mass spectrometric method. The experi mental IE of 8.18 +/- 0.03 eV is in excellent agreement with the theor etical prediction of 8.15 eV calculated using the ab initio Gaussian-2 procedure, indicating that the experimental ionization onset can be a ssigned as the adiabatic IE for CH3SSCH3. The observation of the adiab atic IE(CH3SSCH3) is attributed to the low potential energy barrier fo r rotation about the S-S bond, which allows CH3SSCH3 to exist dynamica lly in a wide range of CSSC dihedral angles.