Publication details for Dr Eckart WredeS. C. Althorpe, F. Fernandez-Alonso, B. D. Bean, J. D. Ayers, A. E. Pomerantz, R. N. Zare & E. Wrede (2002). Observation and interpretation of a time-delayed mechanism in the hydrogen exchange reaction. Nature 416(6876): 67-70.
- Publication type: Journal Article
- ISSN/ISBN: 0028-0836, 1476-4687
- DOI: 10.1038/416067a
- Further publication details on publisher web site
- Durham Research Online (DRO) - may include full text
Author(s) from Durham
Extensive theoretical(1-13) and experimental(2,13-22) studies have shown the hydrogen exchange reaction H + H-2 --> H-2 + H to occur predominantly through a 'direct recoil' mechanism: the H-H bonds break and form concertedly while the system passes straight over a collinear transition state, with recoil from the collision causing the H-2 product molecules to scatter backward. Theoretical predictions agree well with experimental observations of this scattering process(15-20,22). Indirect exchange mechanisms involving H-3 intermediates have been suggested to occur as well(8-13), but these are difficult to test because bimolecular reactions cannot be studied by the femtosecond spectroscopies(23) used to monitor unimolecular reactions. Moreover, full quantum simulations of the time evolution of bimolecular reactions have not been performed. For the isotopic variant of the hydrogen exchange reaction, H + D-2 --> HD + D, forward scattering features(21) observed in the product angular distribution have been attributed(21,12) to possible scattering resonances associated with a quasibound collision complex. Here we extend these measurements to a wide range of collision energies and interpret the results using a full time-dependent quantum simulation of the reaction, thus showing that two different reaction mechanisms modulate the measured product angular distribution features. One of the mechanisms is direct and leads to backward scattering, the other is indirect and leads to forward scattering after a delay of about 25 femtoseconds.