Investigation of radical ions with time-resolved surface enhanced Raman spectroscopy

Time-resolved surface enhanced Raman scattering (TRSERS) spectroscopic methods are discussed for the study of radical ions produced photochemically and electrochemically at silver or gold metal surfaces. Both single shot and pump-probe TRSERS experimental methods are illustrated which use an optical multichannel analyzer, OMA, for ms (single shot) to ns (pump-probe) time resolution. Fundamental chemical and physical processes for photochemically and electrochemically induced radical ion formation are described for adsorbed molecules at the metal-solution interface. Emphasis is given to the possibility of laser photoinduced radical ion formation by a direct molecule-to-metal charge transfer process. Applications of TRSERS techniques are discussed for the study of radical ions formed by various photochemical and electrochemical reactions at the surface of SERS active metals. These adsorbed reaction systems encompass electroreduction processes of adsorbed alkylviologens, p-nitrobenzoate, 4-cyanopyridine, 4-pyridine carboxaldehyde, 4-hydroxymethylpyridine, and direct photoinduced radical cation formation from flavin mononucleotide, FMN.