Quasiclassical trajectory study of the dynamics of the H+N₂O reaction on a new potential energy surface

A new ab initiopotential energy surface (PES) for the H+N₂O→OH+N₂reaction has been constructed using the GROW package of Collins and co-workers. The ab initio calculations have been done using the Becke three-parameter nonlocal exchange functional with the nonlocal correlation of Lee, Yang, and Parr density functional theory. A detailed quasiclassical trajectory study of integral and differential cross sections, product rovibrational populations, and internal energy distributions on the new PES is presented. The theoretical integral cross sections as a function of collision energy are in qualitative agreement with the experimental measurements. A good correspondence is found between the calculated OH(v′=0,1) rovibrational populations and the recent measurements of Brouard and co-workers at 1.48 eV collision energy. In particular, the calculated kinetic energy release distributions for state resolved OH(v′,N′) products predict a substantial fraction of total energy going into rotational excitation of the N₂ co-product, in good agreement with the experimental findings.The Spanish part of this work has been financed by DGES of Spain (Project No. PB98-0762-C02-01) and by the European Commission within the RT Network Reaction Dynamics (Contract No. HPRN-CT-1999-00007)

Universal behavior in complex-mediated reactions: Dynamics of S(1D)+ o-D2 --> D + SD at low collision energies

Reactive and elastic cross-sections, and rate coefficients, have been calculated for the S(1D)+ D2 (v=0, j=0) reaction using a modified hyperspherical quantum reactive scattering method. The considered collision energy ranges from the ultracold regime, where only one partial wave is open, up to the Langevin regime, where many of them contribute. This work presents the extension of the quantum calculations, which were compared with the experimental results in a previous work, down to energies in the cold and ultracold domains. Results are analyzed and compared with the universal case of the quantum defect theory by Jachymski et al. [Phys. Rev. Lett. 110, 213202 (2013)]. State-to-state integral and differential cross sections are also shown covering the ranges of low-thermal, cold and ultracold collision energy regimes. It is found that at E/k_B T < 1 K there are substantial departures from the expected statistical behavior, and that dynamical features become increasingly important with decreasing collision energy, leading to vibrational excitation.Comment: Submitted to Journal of Chemical Physic

Classical collision complexes in the D+H2(v=0, j=0)→HD(v′, j′)+H reaction

Detailed quasiclassical trajectory calculations of the D+H2(v=0, j=0)→HD(v′=0, j′)+H have been carried out in the range of collision energy from 0.35 to 1.25 eV. The calculated v′j′ state resolved differential cross sections and opacity functions show analogous structures to the ones obtained by accurate quantum mechanical results, that is, a peak along a line in the E−θ (or E−J) plane, that was attributed to broad resonances. Analysis of present results in terms of the duration of the collision indicates that those trajectories pertaining to these peaks proceed through the formation of short lived collision complexes with lifetimes of 15–35 fs. © American Institute of PhysicsPartly financed by the CICYT of Spain under Grant No. PB890041.Peer Reviewe

OH+ in astrophysical media: state-to-state formation rates, Einstein coefficients and inelastic collision rates with He

The rate constants required to model the OH$^+$ observations in different regions of the interstellar medium have been determined using state of the art quantum methods. First, state-to-state rate constants for the H$_2(v=0,J=0,1)$+ O$^+$($^4S$) $\rightarrow$ H + OH$^+(X ^3\Sigma^-, v', N)$ reaction have been obtained using a quantum wave packet method. The calculations have been compared with time-independent results to asses the accuracy of reaction probabilities at collision energies of about 1 meV. The good agreement between the simulations and the existing experimental cross sections in the $0.01-$1 eV energy range shows the quality of the results. The calculated state-to-state rate constants have been fitted to an analytical form. Second, the Einstein coefficients of OH$^+$ have been obtained for all astronomically significant ro-vibrational bands involving the $X^3\Sigma^-$ and/or $A^3\Pi$ electronic states. For this purpose the potential energy curves and electric dipole transition moments for seven electronic states of OH$^+$ are calculated with {\it ab initio} methods at the highest level and including spin-orbit terms, and the rovibrational levels have been calculated including the empirical spin-rotation and spin-spin terms. Third, the state-to-state rate constants for inelastic collisions between He and OH$^+(X ^3\Sigma^-)$ have been calculated using a time-independent close coupling method on a new potential energy surface. All these rates have been implemented in detailed chemical and radiative transfer models. Applications of these models to various astronomical sources show that inelastic collisions dominate the excitation of the rotational levels of OH$^+$. In the models considered the excitation resulting from the chemical formation of OH$^+$ increases the line fluxes by about 10 % or less depending on the density of the gas

Beyond universality: parametrizing ultracold complex-mediated reactions using statistical assumptions

We have calculated accurate quantum reactive and elastic cross-sections for the prototypical barrierless reaction D$^{+}$ + H$_2$($v$=0, $j$=0) using the hyperspherical scattering method. The considered kinetic energy ranges from the ultracold to the Langevin regimes. The availability of accurate results for this system allows to test the quantum theory by Jachymski et al. [Phys. Rev. Lett. 110, 213202 (2013)] in a nonuniversal case. The short range reaction probability is rationalized using statistical model assumptions and related to a statistical factor. This provides a means to estimate one of the parameters that characterizes ultracold processes from first principles. Possible limitations of the statistical model are considered

The D+H2(v=1,j)→HD(v′,j′)+H reaction. A detailed quasiclassical trajectory study

Thorough quasiclassical trajectory (QCT) calculations have been carried out for the D+H2(v =1,j) exchange reaction. These calculations include integral and differential cross sections, rate constants, reaction probabilities as a function of total energy, opacity functions, and distributions of internal states of the HD product in the range of collision energies from the reaction threshold to 1.5 eV and initial j values from 0 to 12. An overall good agreement with some discrepancies is found between the present QCT results and those from experiments and accurate quantum-mechanical calculations. © 1994 American Institute of Physics.German-Spanish scientific exchange program >Acciones Integradas HispanoAlemanas,> under Project No. HA-063. Financial support by the DGICYT under Project No. PB92-0219-C03.Peer Reviewe

Influence of the reactants rotational excitation on the H + D2(v = 0, j) reactivity

10 págs.; 10 figs.; 1 tab.; Special Issue: Dynamics of Molecular Collisions XXV: Fifty Years of Chemical Reaction DynamicsWe have analyzed the influence of the rotational excitation on the H + D(v = 0, j) reaction through quantum mechanical (QM) and quasiclassical trajectories (QCT) calculations at a wide range of total energies. The agreement between both types of calculations is excellent. We have found that the rotational excitation largely increases the reactivity at large values of the total energy. Such an increase cannot be attributed to a stereodynamical effect but to the existence of recrossing trajectories that become reactive as the target molecule gets rotationally excited. At low total energies, however, recrossing is not significant and the reactivity evolution is dominated by changes in the collision energy; the reactivity decreases with the collision energy as it shrinks the acceptance cone. When state-to-state results are considered, rotational excitation leads to cold products rovibrational distributions, so that most of the energy is released as recoil energy.The authors acknowledge funding by the Spanish Ministry of Science and Innovation (grant Consolider Ingenio 2010 CSD2009-00038). J.A., F.J.A. and P.G.J. acknowledge also funding by the Spanish Ministry of Economy and Competitiveness (grant CTQ2012-37404-C02), and V.J.H. acknowledges additional funding by the Spanish Ministry of Science and Innovation (FIS2013-48087-C2-1P) and by the European Research Council (ERC-2013-Syg-610256).Peer Reviewe