PHOTOPHYSICS OF HCO2H(A)OVER-TILDE) CLOSE TO ITS ELECTRONIC ORIGIN

A variety of strategies are employed to probe the photophysics of formic acid excited to rovibronic levels close to its A-X band origin. Together with previously published results the data reveal that in this energy regime HCO2H(A) 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 non-radiative 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(A) and the triplet (npi*) state cannot be ruled out.