Strong CIDNP multiplet signals (A/E) for RH and R(-H) were observed from the diffusive encounter of primary, secondary or tertiary alkyl radicals during the reaction of RHgX with S[subscript]2O[subscript]sp82-, S[subscript]2O[subscript]sp82-/I[superscript]- or S[subscript]2O[subscript]sp82-/Ag[superscript]+ at room temperature in reactions involving an electron-transfer of S[subscript]H[superscript]2 process. Net polarization effects (E) for R(-H) were observed from the radical pairs [overline]R•• SO[subscript]sp4-[superscript]F or [overline]R•• NO[subscript]3[superscript]F during the reaction of R[subscript]2Hg with S[subscript]2O[subscript]sp82- or in an electron-transfer reaction with Hg(NO[subscript]3)[subscript]2 at 25°C. Reaction of RCOOH or RCHO with S[subscript]2O[subscript]sp82- at 80°C gave a similar CIDNP signal;The reactions of RHgX or R[subscript]2Hg with S[subscript]2O[subscript]sp82-/I[superscript]- or S[subscript]2O[subscript]sp82-/Ag[superscript]+ have proved to be a good source of alkyl or phenyl radicals which react readily with heteroaromatic compounds, such as pyridine, quinones, maleic anhydride and [alpha],[beta]-unsaturated ketones, diethyl vinylphosphonate or uracil to form substitution or addition products involving free radical chain reactions. The species RHgX[superscript]+•, RHgX[superscript]-• and R• have been probed by MS and ESR spin-trapping experiments;The photostimulated free radical chain reaction of RHgX with pyridines, quinolines, isoquinolines, benzothiazole, pyrazine, N,N,N',N'-tetramethyl-p-phenylene-diamine leads to formation of ring alkylated substitution products.