Photoionization-efficiency (PIE) spectra in the wavelength range of 108-143 nm are measured for C2H5SCl produced from reaction systems Cl/Cl-2/C2H5SH and Cl/Cl-2/C2H5SSC2H5 in a discharge-flow reactor coupled to a photoionization mass spectrometer employing a synchrotron as the source of radiation. According to PIE spectra of C2H5SCl thus obtained, the ionization energy (IE) is (8.994 +/- 0.007) eV. Based on GAUSSIAN-2 calculations, the observed ionization of C2H5SCl near the threshold region is likely to form doublet C2H5SCl+ from singlet C2H5SCl; the calculated IE 8.978 eV agrees well with the experimental value. A vibrational frequency of doublet C2H5SCl+, was found to be (557 +/- 60) cm(-1), which agrees satisfactorily with a theoretical value of 560.9 cm(-1).