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The transition state region of the F + [H.sub.2] reaction has been studied by photoelectron spectroscopy of FH??. New para and normal FH?? photoelectron spectra have been measured in refined experiments and are compared here with exact three-dimensional quantum reactive scattering simulations that use an accurate new ab initio potential energy surface for F + [H.sub.2]. The detailed agreement that is obtained between this fully ab initio theory and experiment is unprecedented for the F + [H.sub.2] reaction and suggests that the transition state region of the F + [H.sub.2] potential energy surface has finally been understood quantitatively., The transition state plays a central role in chemical reaction dynamics (1). Asymptotically observable quantities such as integral cross sections and thermal rate constants often depend crucially on what happens [...]

The van der Waals forces in the entrance valley of the Cl + HD reaction are shown here to pray a decisive role in the reaction's dynamics. Exact quantum mechanical calculations of reactive scattering on a potential energy surface without Cl-HD van der Waals forces predict that the HCl and DCl products will be produced almost equally, whereas the same calculations on a new ab initio potential energy surface with van der Waals forces show a strong preference for the production of DCl. This preference is also seen in crossed molecular beam experiments on the reaction. The study of chemical reaction dynamics has now advanced to the stage where even comparatively weak van der Waals interactions can no longer be neglected in calculations of the potential energy surfaces of chemical reactions., The idea that the structure of the transition state of a chemical reaction determines the overall thermal rate coefficient is deeply ingrained in our understanding of chemical reactions, and it [...]

On page 715 of this issue, Alexander et al. (1) consider the dynamics of an elementary chemical reaction. Unusually, they do so without making the assumption that the Born-Oppeheimer approximation--a [...]

The degree of eLectronic and nucLear coupLing in the CL + H2 reaction has become a vexing probLem in chemicaL dynamics. We report stow eLectron veLocity-map imaging (SEVI) spectra of CLH2- and CLD2-. These spectra probe the reactant valley of the neutral reaction potential energy surface, where nonadiabatic transitions responsible for reactivity of the Cl excited spin-orbit state with H2 wouLd occur. The SEVI spectra reveal progressions in tow-frequency Cl.H2 bending and stretching modes, and are compared to simulations with and without nonadiabatic coupLings between the Cl spin-orbit states. Although nonadiabatic effects are small, their inclusion improves agreement with experiment. This comparison vatidates the theoretical treatment, especially of the nonadiabatic effects, in this critical region of the CL + H2 reaction, and suggests strongty that these effects are minor. [ABSTRACT FROM AUTHOR]

Photodetachment spectroscopy of the FH2- and FD2- anions allows for the direct observation of reactive resonances in the benchmark reaction F + H2 → HF + H. Using cooled anion precursors and a high-resolution electron spectrometer, we observe several narrow peaks not seen in previous experiments. Theoretical calculations, based on a highly accurate F + H2 potential energy surface, convincingly assign these peaks to resonances associated with quasibound states in the HF + H and DF + D product arrangements and with a quasibound state in the transition state region of the F + H2 reaction. The calculations also reveal quasibound states in the reactant arrangement, which have yet to be resolved experimentally. [ABSTRACT FROM AUTHOR]

Photodetachment spectroscopy of the FH2(-) and FD2(-) anions allows for the direct observation of reactive resonances in the benchmark reaction F + H2 → HF + H. Using cooled anion precursors and a high-resolution electron spectrometer, we observe several narrow peaks not seen in previous experiments. Theoretical calculations, based on a highly accurate F + H2 potential energy surface, convincingly assign these peaks to resonances associated with quasibound states in the HF + H and DF + D product arrangements and with a quasibound state in the transition state region of the F + H2 reaction. The calculations also reveal quasibound states in the reactant arrangement, which have yet to be resolved experimentally., (Copyright © 2015, American Association for the Advancement of Science.)