The direct photoinduced charge transfer from adsorbed flavin mononucleotide (FMN) to a Ag electrode was observed by time-resolved surface-enhanced Raman scattering (TRSERS), electrochemistry, and photogalvanic effect studies. Two short-lived photoproduct radical ion intermediates were observed by TRSERS of FMN and confirmed by normal mode calculations as enol-keto forms of a photo-oxidized flavin monocation radical in aqueous and deuterated solution. The enol configuration of the FMN cation forms by electron injection to the metal and intramolecular proton transfer from N3-H to the C2=0 keto group on ring III at times faster than 75 ns upon 350 or 337 nm excitation. By 775 ns the proton transfers from the C2-OH enol group back to the N3 atom of ring III of the FMN cation. Photo-oxidation to the keto form of the radical cation occurs on excitation with Light from 450 to 610 nm. The radical cation decays back to FMN by 1.5 mu s. Surface concentrations of adsorbed FMN on the Ag electrode were estimated by linear sweep voltammetry and were found to be less than a monolayer. New mechanisms of photoinduced charge transfer between FMN and a Ag electrode and the photogalvanic effect on a dye-modified metal electrode are proposed as a result of the experiments.