Effect of vibrational excitation on the reactivity of D+MuH(v=1)

ISMB2015, 28 junio al 3 de julio de 2015, Segovia (España); http://www.ucm.es/ismbPeer Reviewe

Cumulative reaction probabilities and transition state properties: A study of the H++H2 and H++D2 proton exchange reactions

10 pages, 6 figures.Cumulative reaction probabilities (CRPs) have been calculated by accurate (converged, close coupling) quantum mechanical (QM), quasiclassical trajectory (QCT), and statistical QCT (SQCT) methods for the H++H2 and H++D2 reactions at collision energies up to 1.2 eV and total angular momentum J=0–4. A marked resonance structure is found in the QM CRP, most especially for the H system and J=0. When the CRPs are resolved in their ortho and para contributions, a clear steplike structure is found associated with the opening of internal states of reactants and products. The comparison of the QCT results with those of the other methods evinces the occurrence of two transition states, one at the entrance and one at the exit. At low J values, except for the quantal resonance structure and the lack of quantization in the product channel, the agreement between QM and QCT is very good. The SQCT model, that reflects the steplike structure associated with the opening of initial and final states accurately, clearly tends to overestimate the value of the CRP as the collision energy increases. This effect seems more marked for the H++D2 isotopic variant. For sufficiently high J values, the growth of the centrifugal barrier leads to an increase in the threshold of the CRP. At these high J values the discrepancy between SQCT and QCT becomes larger and is magnified with growing collision energy. The total CRPs calculated with the QCT and SQCT methods allowed the determination of the rate constant for the H++D2 reaction. It was found that the rate, in agreement with experiment, decreases with temperature as expected for an endothermic reaction. In the range of temperatures between 200 and 500 K the differences between SQCT and QCT rate results are relatively minor. Although exact QM calculations are formidable for an exact determination of the k(T), it can be reliably expected that their value will lie between those given by the dynamical and statistical trajectory methods.This work has been funded by the MICIN (Spain) under Project Nos. CTQ2008-02578, CTQ2005-09185, FIS2007- 62006 ENE2006-14577-C04-Co3/FTN, and FIS2007-61686. P.G.J. also acknowledge support from the fellowship Grant No. Grant AP2006-03740.Peer reviewe

A comparison of quantum and quasiclassical statistical models for reactions of electronically excited atoms with molecular hydrogen

12 pags. ; 13 figs.A detailed comparison of statistical models based on the quasiclassical trajectory SQCT and quantum mechanical SQM methods is presented in this work for the C 1 D +H2 , S 1 D +H2 , O 1 D +H2 and N 2 D +H2 insertion reactions. Reaction probabilities, integral ICS and differential DCS cross sections at different levels of product’s state resolution are shown and discussed for these reactions. The agreement is in most cases excellent and indicates that the effect of tunneling through the centrifugal barrier is negligible. However, if there exists a dynamical barrier, as in the case of the N 2 D +H2 reaction, some of the SQM results can be slightly different than those calculated with the SQCT model. The rationale of the observed similarities and discrepancies can be traced back to the specific topologies of the potential energy surfaces for each of the reactions examined. The SQCT model is sensitive enough to show the relatively small inaccuracies resulting from the decoupling inherent to the centrifugal sudden approximation when used in the SQM calculations. In addition, the effect of ignoring the parity conservation is also examined. This effect is in general minor except in particular cases such as the DCS from initial rotational state j=0, which requires, in order to reproduce the sharp forward and backward peaks, the explicit conservation of parity. © 2008 American Institute of PhysicsThe authors acknowledge funding by the Spanish Ministry of Education and Science Grant Nos. CTQ2005-08493-C01-01 and FIS2007-62006 .Peer reviewe

Cumulative reaction probabilities and transition state properties: A study of the F+ H2 reaction and its deuterated isotopic variants

9 pags., 9 figs.A comparative quantum mechanical (QM) and quasiclassical trajectory (QCT) study of the cumulative reaction probabilities (CRPs) is presented in this work for the F+ H2 reaction and its isotopic variants for low values of the total angular momentum J. The agreement between the two sets of calculations is very good with the exception of some features whose origin is genuinely QM. The agreement also extends to the CRP resolved in the helicity quantum number k. The most remarkable feature is the steplike structure, which becomes clearly distinct when the CRPs are resolved in odd and even rotational states j. The analysis of these steps shows that each successive increment is due to the opening of the consecutive rovibrational states of the H2 or D2 molecule, which, in this case, nearly coincide with those of the transition state. Moreover, the height of each step reflects the number of helicity states compatible with a given J and j values, thus indicating that the various helicity states for a specific j have basically the same contribution to the CRPs at a given total energy. As a consequence, the dependence with k of the reactivity is practically negligible, suggesting very small steric restrictions for any possible orientation of the reactants. This behavior is in marked contrast to that found in the D+ H2 reaction, wherein a strong k dependence was found in the threshold and magnitude of the CRP. The advantages of a combined QCT and QM approaches to the study of CRPs are emphasized in this work. © 2008 American Institute of Physics.This work was financed by the Spanish Ministry of Education and Science Grant Nos. CTQ2005-08493, ENE2006-14577-C04-C03/FTN, and FIS2007-61686. The research was performed within the Unidad Asociada “Química Física Molecular” between the Universidad Complutense and the CSIC

Orbiting resonances in the F + HD (: V = 0, 1) reaction at very low collision energies. A quantum dynamical study

Time-independent, fully converged, quantum dynamical calculations have been performed for the F + HD (v = 0, j = 0) and F + HD (v = 1, j = 0) reactions on an accurate potential energy surface down to collision energies of 0.01 meV. The two isotopic exit channels, HF + D and DF + H, have been investigated. The calculations reproduce satisfactorily the Feshbach resonance structures for collision energies between 10 and 40 meV, previously reported in the literature for the HF + D channel. Contrary to the results of a former literature work, vibrational excitation of HD is found to enhance reactivity in all cases down to the lowest collision energy investigated. Shape-type orbiting resonances are found for collision energies lower than 2 meV. The resonances appear as peaks in the reaction cross sections that are associated to specific values of the total angular momentum, J. In contrast with the Feshbach resonances at higher energies, the orbiting resonance structure, which is caused by the van der Waals well of the entrance channel, is identical for the HF + D and DF + H exit channels. The orbiting resonance peaks for F + HD (v = 0) are very small, but those for F + HD (v = 1) could be observed, in principle, with a combination of Raman pumping and merged beams methods.This work has been funded by the meiyu of Spain under grant PGC2018-09644-B-100 and by the MINECO of Spain under grants , CTQ-2015-65033-P and FIS2016-77726-C3-1P. VJH acknowledges also funding from the EU project ERC-2013-Syg 610256. The research was conducted within the Unidad Asociada between the Department of Physical Chemistry of the UCM and the CSIC of Spai

Cumulative reaction probabilities: a comparison between quasiclassical and quantum mechanical results

This article presents a quasiclassical trajectory (QCT) method for determining the cumulative reaction probability (CRP) as a function of the total energy. The method proposed is based on a discrete sampling using integer values of the total and orbital angular momentum quantum numbers for each trajectory and on the development of equations that have a clear counterpart in the quantum mechanical (QM) case. The calculations comprise cumulative reaction probabilities at a given total angular momentum J, as well as those summed over J. The latter are used to compute QCT rate constants. The method is illustrated by comparing QCT and QM results for the H + H2, H + D2, D + H2, and H + HD reactions. The agreement between QCT and QM results is very good, with small discrepancies between the two data sets indicating some genuine quantum effects. The most important of these involves the value of the CRP at low energies which, due to the absence of tunneling, is lower in the QCT calculations, causing the corresponding rate constants to be smaller. The second is the steplike structure that is clearly displayed in the QM CRP for J=0, which is much smoother in the corresponding QCT results. However, when the QCT density of reactive states, i.e., the derivatives fo the QCT CRP with respect to the energy, is calculated, a succession of maxima and minima is obtained which roughly resembles those found in the QM calculations, although the latter are considerably sharper. The analysis of the broad peaks in the OCT density of reactive states indicates that the distributions of collision times associated with the maxima are somewhat broader, with a tail extending to larger collision times, than those associated with the mimima. In addition, the QM and QCT dynamics of the isotopic variants mentioned above are compared in the light of their CRPs. Issues such as the compliance of the QCT CRP with the law of microscopic reversibility, as well as the similarity between the CRPs for ortho and para species in the QM and QCT cases, are also addressed

Cumulative reaction probabilities: a comparison between quasiclassical and quantum mechanical results

This article presents a quasiclassical trajectory (QCT) method for determining the cumulative reaction probability (CRP) as a function of the total energy. The method proposed is based on a discrete sampling using integer values of the total and orbital angular momentum quantum numbers for each trajectory and on the development of equations that have a clear counterpart in the quantum mechanical (QM) case. The calculations comprise cumulative reaction probabilities at a given total angular momentum J, as well as those summed over J. The latter are used to compute QCT rate constants. The method is illustrated by comparing QCT and QM results for the H + H2, H + D2, D + H2, and H + HD reactions. The agreement between QCT and QM results is very good, with small discrepancies between the two data sets indicating some genuine quantum effects. The most important of these involves the value of the CRP at low energies which, due to the absence of tunneling, is lower in the QCT calculations, causing the corresponding rate constants to be smaller. The second is the steplike structure that is clearly displayed in the QM CRP for J=0, which is much smoother in the corresponding QCT results. However, when the QCT density of reactive states, i.e., the derivatives fo the QCT CRP with respect to the energy, is calculated, a succession of maxima and minima is obtained which roughly resembles those found in the QM calculations, although the latter are considerably sharper. The analysis of the broad peaks in the OCT density of reactive states indicates that the distributions of collision times associated with the maxima are somewhat broader, with a tail extending to larger collision times, than those associated with the mimima. In addition, the QM and QCT dynamics of the isotopic variants mentioned above are compared in the light of their CRPs. Issues such as the compliance of the QCT CRP with the law of microscopic reversibility, as well as the similarity between the CRPs for ortho and para species in the QM and QCT cases, are also addressed

Can quasiclassical trajectory calculations reproduce the extreme kinetic isotope effect observed in the muonic isotopologues of the H + H2 reaction?

Rate coefficients for the mass extreme isotopologues of the H + H 2 reaction, namely, Mu H2, where Mu is muonium, and He H2, where He is a He atom in which one of the electrons has been replaced by a negative muon, have been calculated in the 200-1000 K temperature range by means of accurate quantum mechanical (QM) and quasiclassical trajectory (QCT) calculations and compared with the experimental and theoretical results recently reported by Fleming [Science 331, 448 (2011)]10.1126/science.1199421. The QCT calculations can reproduce the experimental and QM rate coefficients and kinetic isotope effect (KIE), kMu(T)kHe(T), if the Gaussian binning procedure (QCT-GB) - weighting the trajectories according to their proximity to the right quantal vibrational action - is applied. The analysis of the results shows that the large zero point energy of the MuH product is the key factor for the large KIE observed. © 2011 American Institute of Physics.Funding by the Spanish Ministry of Science and Innovation (Grant Nos. CTQ2008-02578, FIS2010-16455, and Consolider Ingenio 2010 CSD2009-00038). P.G.J. acknowledges the FPU fellowship AP2006-03740. The research was conducted within the Unidad Asociada Química Física Molecular between the UCM and the CSIC of Spain.Peer Reviewe

A statistical quasiclassical trajectory model for atom-diatom insertion reactions.

A statistical model based on the quasiclassical trajectory method is presented in this work for atom-diatom insertion reactions. The basic difference between this and the corresponding statistical quantum model (SQM) lies in the fact that trajectories instead of wave functions are propagated in the entrance and exit channels. Other than this the two formulations are entirely similar. In particular, it is shown that conservation of parity can be taken into account in a natural and precise way in the statistical quasiclassical trajectory (SQCT) model. Additionally, the SQCT model complies with the principle of detailed balance and overcomes the problem of the zero point energy in the products. As a test, the model is applied to the H3+ and H+D2 exchange reactions. The excellent agreement between the SQCT and SQM results, especially in the case of the differential cross sections, indicates that the effect of tunneling through the centrifugal barrier is negligible. The effect of ignoring quantum mechanical parity conservation is also investigated

Classical trajectory calculations for the D+H2(v=0, j=0-3)→HD(v′, j′)+H reaction: Differential and state-to-state cross sections in the 0.35-1.10 eV collision energy range

Differential and total state-to-state cross sections for the D + H2 (v=0, j=0-3) → HD (v′, j′) + H reaction in the 0.35-1.10 eV collision energy range, have been calculated on the LSTH surface using the QCT method. The results are commented on and compared to recent quantum mechanical calculations and to experimental measurements. © 1990 Published by Elsevier B.V.Financed in part by the CICYT of Spain under Grant PB 870263.Peer Reviewe