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Wave packets in a bifurcating region of an energy landscape: Diels-Alder dimerization of cyclopentadiene ; Dive, Georges ; Desouter, Michèle in Journal of Chemical Physics (2005), 122(18), 1843041-10 Quantum dynamics in a valley ridge inflection (VRI) point region is analyzed in the case of the Diels-Alder endo-dimerization of cyclopentadiene pointed out recently by [Caramella , J. Am. Chem. Soc. 124 ... [more ▼] Quantum dynamics in a valley ridge inflection (VRI) point region is analyzed in the case of the Diels-Alder endo-dimerization of cyclopentadiene pointed out recently by [Caramella , J. Am. Chem. Soc. 124, 1130 (2002)]. The VRI point is located along the reaction path connecting the bispericyclic symmetrical transition structure put in evidence by Caramella and the transition state of the Cope rearrangement. Dynamics is carried out by using constrained Hamiltonian methodology. The active coordinates are the first formed C-C bond length and the difference between the two other C-C bond lengths which achieve the dimerization as 4+2 or 2+4 adducts. A two-dimensional (2D) minimum-energy surface have been computed at the Becke 3 Lee-Yong-Parr/6-31G(*) level. The energy landscape can be classified as an uphill ridge-pitchfork VRI bifurcation according to a recent classification of bifurcation events [W. Quapp, J. Mol. Struct. 695-696, 95 (2004)]. Dynamics does not describe the thermal reaction but concerns wave packets which could be prepared by pulse reagents, i.e., by coherent control. We analyze how the shape and initial location on the ground potential-energy surface are linked to the synchronous or asynchronous mechanism of the final step after the first transition state. We use a one-dimensional model of optimum control theory to check the feasibility of such a coherent preparation. The wave-packet evolution in the VRI domain is well explained by semiclassical predictions even with the negative curvature of the unstable ridge. Finally, a crude model of dissipation has been introduced to test the stability of the 2D predictions. (c) 2005 American Institute of Physics. [less ▲] Detailed reference viewed: 25 (0 ULg)Non-adiabatic interactions in wave packet dynamics of the bromoacetyl chloride photodissociation ; ; et al in Journal of Chemical Physics (2004), 120(3), 1271-1278 Detailed reference viewed: 8 (0 ULg)Cumulative isomerization probability by various transition state wave packet methods including the MCTDH algorithm ; ; et al in Journal of Chemical Physics (2004), 121 Detailed reference viewed: 4 (0 ULg)Wave packet dynamics along bifurcating reaction paths ; Dive, Georges ; et al in Journal of Chemical Physics (2003), 118(13), 5831-5840 The problem of bifurcating reaction paths is revisited by wave packet (WP) dynamics. The pitchfork model connecting five stationary points-a reactive, two transition structures and two enantiomeric ... [more ▼] The problem of bifurcating reaction paths is revisited by wave packet (WP) dynamics. The pitchfork model connecting five stationary points-a reactive, two transition structures and two enantiomeric products-is characterized by a Valley Ridge inflection point (VRI) where WP could leave the standard intrinsic reaction path. We question the role of such a VRI point to determine whether the mechanism is sequential or concerted. WP simulations on two-dimensional minimum energy surfaces are carried out in the benchmark case of the methoxy radical isomerization H3CO-->H2COH. The ab initio potential energy surface (PES) is fitted to an analytical model which is bent to analyze the incidence of geometrical parameters on the WP behavior. For each of these generated PES, the WP width in the entrance valley is the main factor which conditions the behavior on the unstable ridge. The WP evolution is also analyzed in terms of nonadiabatic transitions among adiabatic channels along the reaction coordinate. Finally, the location of VRI points according to an invariant definition is discussed. (C) 2003 American Institute of Physics. [less ▲] Detailed reference viewed: 26 (0 ULg)Non-adiabatic effects in photodissociation of bromoacetyl chloride ; ; et al in Chemical Physics Letters (2003), 374 Detailed reference viewed: 3 (0 ULg)Cumulative reaction probability by constrained dynamics: H transfer in HCN, H2CO, and H3CO ; ; et al in Journal of Chemical Physics (2002), 117(2), 727-739 A strategy to obtain quantum corrections to the cumulative reaction probability from a subspace of active coordinates is analyzed. The kinetic energy operator exactly takes into account the constraints ... [more ▼] A strategy to obtain quantum corrections to the cumulative reaction probability from a subspace of active coordinates is analyzed. The kinetic energy operator exactly takes into account the constraints due to inactive coordinates. The geometry of the inactive skeleton is adiabatically adjusted to the dynamical variables or simply frozen according to the coupling to the active space. Dynamics is carried out using the curvilinear coordinates of the Z-matrix so that computation of the potential energy surface and dynamics are coupled. The cumulative reaction probability N(E) is obtained directly in a large range of energy by a time independent formulation of the Zhang and Light transition state wave packet method. N-nD(E) is first computed in the active n-dimensional space and then convoluted with a bath. The efficiency of the Chebyshev expansion of the microcanonical projection operator delta(E-(H) over cap (nD)) appearing in the quantum expression of N-nD(E) is checked. The method is implemented for the study of tunneling effect in H transfer. The coordinates are three spherical coordinates referred to the frozen or adiabatic skeleton. We compare the quantum corrections brought about by different 2D groups of internal coordinates. (C) 2002 American Institute of Physics. [less ▲] Detailed reference viewed: 24 (0 ULg) |
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