The photochemistry of NCS^- in solution

The photochemistry of NCS^- was investigated at wavelengths within its charge-transfer-to-solvent (CTTS) absorption band. Only a small yield of solvated electrons was detected; most of the excited ions dissociate to give CN^- (or HCN) + S pairs, which undergo efficient cage recombination. The increase of the quantum yield with NCS^- concentration is ascribed to self-scavenging: NCS^- scavenges the sulfur atom from the cage. This mechanism is verified by the use of allyl alcohol as a foreign scavenger for S atoms. The photolysis is strongly affected by varying the acidity around pH 7.5. This is attributed to acid-base equilibrium involving the excited ion.