The title reactions have been investigated in the gas phase using UV photoelectron spectroscopy. By recording spectra at different reaction times, it was possible to detect reaction intermediates and hence identify pathways by which each reaction proceeds. The Fe-2 + CH3SCH3 reaction appears to proceed via the intermediate CH3SFCH3 whereas the F-2 + CH3SSCH3 reaction gives H2CS and HF as the first observed products. Far both reactions at longer reaction times, a new spectrum associated with a reaction product, consisting of three. photoelectron bands with adiabatic ionization energies of 10.15 +/- 0.01 +/- 11.49 +/- 0.02, and 13.71 +/- 0.01 eV, has been observed. This spectrum is assigned to the HFCS molecule. The first two adiabatic ionization energies of HFCS have been calculated using the Gaussian-2 (G2) theoretical procedure as 10.09 and 11.51 eV, respectively, supporting this assignment. This work represents the first observation and spectroscopic study of this molecule. A broad band with a vertical ionization energy of 10.58 +/- 0.06 eV, assigned to the first ionization energy of HCF, has also been observed as a secondary product from both reactions under conditions of excess F-2 partial pressure. This assignment is supported by first adiabatic and vertical ionization energies of HCF computed at the G2 level of theory. For each reaction, a reaction mechanism is proposed on the basis of the results obtained.