Excited-state dynamics of hydrogen-bonded dimers of benzoic acid

The fluorescence emission spectra of jet-cooled hydrogen-bonded dimers of benzoic acid and isotopic analogs are presented and the vibrational assignments of the ground state complexes are made. Intramolecular vibrational relaxation is observed in S1 at excess vibrational energies as low as 373 cm−1. The role of the hydrogen bonding network as a heat bath is considered and the results are consistent with an argument based on an estimate of the density of states. Electronic energy transfer is examined in the weak coupling limit and transfer is observed in mixed dimers of perhydro (d0) and ring deuterated (d5) benzoic acid. Transfer from d5 to d0 is observed when excess vibrational energy is present. The jet-cooled, isolated dimer provides an excellent case for the examination of energy transfer in hydrogen-bonded complexes.