@article{BartlettJankunasGoswamietal.2011, author = {Bartlett, Nate C. -M. and Jankunas, Justin and Goswami, Tapas and Zare, Richard N. and Bouakline, Foudhil and Althorpe, Stuart C.}, title = {Differential cross sections for H + D-2 -> HD(v '=2, j '=0,3,6,9) + D at center-of-mass collision energies of 1.25, 1.61, and 1.97 eV}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {18}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c0cp02460k}, pages = {8175 -- 8179}, year = {2011}, abstract = {We have measured differential cross sections (DCSs) for the reaction H + D-2 -> HD- (v' = 2, j' = 0,3,6,9) + D at center-of-mass collision energies E-coll of 1.25, 1.61, and 1.97 eV using the photoloc technique. The DCSs show a strong dependence on the product rotational quantum number. For the HD(v' = 2, j' = 0) product, the DCS is bimodal but becomes oscillatory as the collision energy is increased. For the other product states, they are dominated by a single peak, which shifts from back to sideward scattering as j' increases, and they are in general less sensitive to changes in the collision energy. The experimental results are compared to quantum mechanical calculations and show good, but not fully quantitative agreement.}, language = {en} } @article{JankunasZareBouaklineetal.2012, author = {Jankunas, Justin and Zare, Richard N. and Bouakline, Foudhil and Althorpe, Stuart C. and Herraez-Aguilar, Diego and Aoiz, F. Javier}, title = {Seemingly anomalous angular distributions in H+D-2 reactive scattering}, series = {Science}, volume = {336}, journal = {Science}, number = {6089}, publisher = {American Assoc. for the Advancement of Science}, address = {Washington}, issn = {0036-8075}, doi = {10.1126/science.1221329}, pages = {1687 -- 1690}, year = {2012}, abstract = {When a hydrogen (H) atom approaches a deuterium (D-2) molecule, the minimum-energy path is for the three nuclei to line up. Consequently, nearly collinear collisions cause HD reaction products to be backscattered with low rotational excitation, whereas more glancing collisions yield sideways-scattered HD products with higher rotational excitation. Here we report that measured cross sections for the H + D-2 -> HD(v' = 4, j') + D reaction at a collision energy of 1.97 electron volts contradict this behavior. The anomalous angular distributions match closely fully quantum mechanical calculations, and for the most part quasiclassical trajectory calculations. As the energy available in product recoil is reduced, a rotational barrier to reaction cuts off contributions from glancing collisions, causing high-j' HD products to become backward scattered.}, language = {en} } @article{BouaklineAlthorpeLarregarayetal.2010, author = {Bouakline, Foudhil and Althorpe, Stuart C. and Larregaray, Pascal and Bonnet, Laurent}, title = {Strong geometric-phase effects in the hydrogen-exchange reaction at high collision energies : II. quasiclassical trajectory analysis}, issn = {0026-8976}, doi = {10.1080/00268971003610218}, year = {2010}, abstract = {Recent calculations on the hydrogen-exchange reaction [Bouakline et al., J. Chem. Phys. 128, 124322 (2008)], have found strong geometric phase (GP) effects in the state-to-state differential cross-sections (DCS), at energies above the energetic minimum of the conical intersection (CI) seam, which cancel out in the integral cross-sections (ICS). In this article, we explain the origin of this cancellation and make other predictions about the nature of the reaction mechanisms at these high energies by carrying out quasiclassical trajectory (QCT) calculations. Detailed comparisons are made with the quantum results by splitting the quantum and the QCT cross-sections into contributions from reaction paths that wind in different senses around the CI and that scatter the products in the nearside and farside directions. Reaction paths that traverse one transition state (1-TS) scatter their products in just the nearside direction, whereas paths that traverse two transition states (2-TS) scatter in both the nearside and farside directions. However, the nearside 2-TS products scatter into a different region of angular phase-space than the 1-TS products, which explains why the GP effects cancel out in the ICS. Analysis of the QCT results also suggests that two separate reaction mechanisms may be responsible for the 2-TS scattering at high energies.}, language = {en} }