Infrared spectroscopy of OHH2 entrance channel complexes

Spectroscopic implications of the coupling of unquenched angular momentum to rotation in OH-containing complexes

A model is developed for the rotational energy levels and electric dipole transition intensities of nonlinear OH-containing complexes in which the OH is hydrogen bonded to its partner. Both the 2A' and 2A" electronic states arising from the lifting of the OH monomer electronic orbital degeneracy are explicitly included. Consequently, the model smoothly spans the entire range of the difference potential associated with the separation between these two states, and the model accounts for the partial quenching of the OH monomer electronic angular momentum in such complexes. The more familiar cases of completely unquenched and completely quenched electronic angular momentum are recovered in the limits of zero and very large difference potential, respectively. The sensitivity of rovibrational spectra to the value of the difference potential is investigated, and it is shown that spectra of reactant complexes reveal the extent of quenching, which must occur along the reaction coordinate as the system evolves from weakly interacting partners to addition product. The model is successfully applied to the analysis of the OH overtone spectrum of the OH-acetylene complex.

Quantum theory of chemical reaction dynamics

It is now possible to use rigorous quantum scattering theory to perform accurate calculations on the detailed state-to-state dynamics of chemical reactions in the gas phase. Calculations on simple reactions, such as H + D2 --> HD + D and F + H2 --> HF + H, compete with experiment in their accuracy. Recent advances in theory promise to extend such accurate predictions to more complicated reactions, such as OH + H2 --> H2O + H, and even to reactions of molecules on solid surfaces. New experimental techniques for probing reaction transition states, such as negative-ion photodetachment spectroscopy and pump-probe femtosecond spectroscopy, are stimulating the development of new theories.