The radical anion (Ph₃CSSH).- has been trapped at low temperature in an X-irradiated single crystal of (triphenylmethyl) disulfane. The g and ¹H hyperfine tensors are obtained and their eigenvectors are compared with the crystallographic bond directions. The optimized geometries for CH₃SSH, HSSH.-, and (CH₃SSH).- are obtained from ab initio calculations (6-31G* basis set). The theoretical ¹H anisotropic coupling tensors, obtained by evaluating the expectation value of the dipolar operator for (CH₃SSH).-, are compared with the present experimental values (for the S-H proton) and with recent literature data (for the proton bound to the carbon atom).