A photoionization-efficiency spectrum of CH3SCH2Cl was measured over the wavelength range 108-142 nm by means of a photoionization mass spectrometer coupled to a synchrotron as the source of radiation. Gaseous CH3SCH2Cl was generated in a discharge-flow reactor involving Cl, Cl-2, and CH3SCH3 at room temperature via these sequential reactions: Cl + CH3SCH3--> CH3SCH2 + HCl; CH3SCH2 + Cl-2--> CH3SCH2Cl + Cl. According to the PIE spectrum of CH3SCH2Cl thus obtained, the ionization energy is (9.077 +/-0.007) eV. Based on GAUSSIAN-2 calculations, the observed ionization of CH3SCH2Cl near the threshold region is likely to form from singlet CH3SCH2Cl ionizing to doublet CH3SCH2Cl+; the calculated ionization energy 9.064 eV agrees with the experimental value. The adiabatic ionization energy of CH3SCH2 and appearance energy of CH3SCH2+ from CH3SCH2Cl were determined to be (6.884 +/-0.008) eV and (10.007 +/-0.016) eV, respectively; the dissociation energy of the CH3SCH2-Cl bond is thus derived to be (72.0 +/-0.6) kcal mol(-1). (C) 2001 American Institute of Physics.