The E.S.R. spectra of the radicals generated by photolysis of triphenylmethyldisulphane are studied. The E.S.R. eigenvectors are compared to the bond directions in the parent molecule determined from the crystal structure of Ph₃CSSH (space group P2₁2₁2₁, a=7·571(1), b=7·608(1), c=27·790(5), Z=4). Pairs of Ph₃CSS radicals are trapped, with zero field parameters D=235 MHz and E=4 MHz, in addition to the Ph₃CS radicals. The crystal structure causes the formation and the stereospecificity of the radical pairs, a mechanism for this effect is suggested.