A diabatic state model for donor-hydrogen vibrational frequency shifts in hydrogen bonded complexes

► Two diabatic state Hamiltonian describes weak, low-barrier, and strong hydrogen bonds. ► Describes red (blue) shift of donor-hydrogen stretch (bend) with decreasing donor-acceptor distance. ► Describes correlation of D-H stretch frequency with difference between donor and acceptor proton affinity. ► Predicts UV photo-dissociation of strong H-bonded complexes via a 'twin' excited electronic state. ► Two parameter model quantitatively describes empirical correlations for wide range of H-bonded complexes.