Adiabatic ionization energy of CH3SSCH3

The ionization energy (IE) for CH3SSCH3 has been measured by the pulsed molecular beam photoionization mass spectrometric method. The experimental IE of 8.18±0.03 eV is in excellent agreement with the theoretical prediction of 8.15 eV calculated using the ab initio Gaussian-2 procedure, indicating that the experimental ionization onset can be assigned as the adiabatic IE for CH3SSCH3. The observation of the adiabatic IE(CH3SSCH3) is attributed to the low potential energy barrier for rotation about the S–S bond, which allows CH3SSCH3 to exist dynamically in a wide range of CSSC dihedral angles.