Photophysics of HCO2H(Ã) close to its electronic origin

Abstract

A variety of strategies are employed to probe the photophysics of formic acid axcited to rovibronic levels close to its ÖX band origin. Together with previously published results the data reveal that in this energy regime HCO₂H(Ã) decays primarily non-radiatively but does not dissociate to OH and HCO, which are the dominant photofragments when formic acid is excited at shorter wavelengths. It is proposed that the most likely nonradiative pathway is internal conversion to the ground electronic state following which dissociation will occur probably via molecular elimination to H₂O + CO. Detailed rovibronic state selective fluorescence lifetime measurements are shown to be consistent with the above mechanism, although weak additional coupling between HCO₂H(Ã) and the triplet (nπ*) state cannot be ruled out.