Recent attention to cold environments, either in the laboratory or under astrophysical and other conditions, is putting at the forefront the tunnel effect, a principal source of deviations from the Arrhenius rate law. Progress in theoretical chemical kinetics relies on accurate knowledge of potential energy surfaces, as provided by advanced quantum chemistry and tested against experiments. To generate accurate rate data, quantum scattering calculations involve sophisticated algorithms to produce scattering matrix elements at given angular momenta (to be summed to yield cross sections) and as a function of collision velocities (to be integrated to give rate constants and temperature dependencies). Here illustrated are these passages, a milestone having been benchmark temperature dependent rate constants for the prototypical F + H2 reaction [1], recently validated by experiments in the moderate tunnelling regime [2]. The F+ HD variant permits exploring tunnel as well as isotopic effects [3] and developing a phenomenology and interpretive ingredients down to the deep tunnelling regime [4-6]. Accurate data are becoming available for other reactions [7,8]. [1]V. Aquilanti, S. Cavalli, D. De Fazio, A. Volpi, A. Aguilar, J. M. Lucas " Benchmark rate constants by the hyperquantization algorithm. The F + H2 reaction for various potential energy surfaces: features of the entrance channel and of the transition state, and low temperature reactivity" Chem. Phys. 308, 237-253 (2005) [2] M. Tizniti, S. D. Le Picard, F. Lique, C. Berteloite, A. Canosa, M. H. Alexander, I. R. Sims "The rate of the F + H2 reaction at very low temperatures". Nature Chemistry., 6, 141-145 (2014) [3] D. De Fazio, V. Aquilanti, S. Cavalli, A. Aguilar, J. M. Lucas "Exact quantum calculations of the kinetic isotope effect: Cross sections and rate constants for the F + HD reaction and role of tunnelling" J.Chem. Phys. 125, 133109 (9 pages) (2006) [4] V. Aquilanti, K.C. Mundim, S. Cavalli, D. De Fazio, A. Aguilar, J. M. Lucas "Exact activation energies and phenomenological description of quantum tunneling for model potential energy surfaces. The F + H2 reaction at low temperature" Chemical Physics, 398,186-191 (2012) [5] V. H. C. Silva, V. Aquilanti, H. C. B. de Oliveira, K. C. Mundim "Uniform description of non-Arrhenius temperature dependence of reaction rates, and a heuristic criterion for quantum tunneling vs classical non-extensive distribution" Chem.Phys.Letters, 590, 201-207 (2013) [6] S. Cavalli, V. Aquilanti, K. C. Mundim, D De Fazio "Theoretical reaction kinetics astride the transition between moderate and deep tunneling regimes: the F + HD case", J Phys Chem A, 118, 6632-6641 (2014). [7] M. B. Krasilnikov, R. S. Popov, O. Roncero, D. De Fazio, S. Cavalli, V. Aquilanti, O. S. Vasyutinskii; "Polarization of molecular angular momentum in the chemical reactions Li+HF and F+HD" J. Chem. Phys. 138, 244302 (2013). [8] D. De Fazio, M. de Castro-Vitores, A. Aguado, V. Aquilanti, S. Cavalli " The He + H2+ -> HeH+ + H reaction: Ab initio studies of the potential energy surface, benchmark time-independent quantum dynamics in an extended energy range and comparison with experiments" J. Chem. Phys. 137, 244306 (2012)
Benchmarking reaction kinetics astride the transition between the moderate and deep tunnelling regimes
Dario De Fazio;
2015
Abstract
Recent attention to cold environments, either in the laboratory or under astrophysical and other conditions, is putting at the forefront the tunnel effect, a principal source of deviations from the Arrhenius rate law. Progress in theoretical chemical kinetics relies on accurate knowledge of potential energy surfaces, as provided by advanced quantum chemistry and tested against experiments. To generate accurate rate data, quantum scattering calculations involve sophisticated algorithms to produce scattering matrix elements at given angular momenta (to be summed to yield cross sections) and as a function of collision velocities (to be integrated to give rate constants and temperature dependencies). Here illustrated are these passages, a milestone having been benchmark temperature dependent rate constants for the prototypical F + H2 reaction [1], recently validated by experiments in the moderate tunnelling regime [2]. The F+ HD variant permits exploring tunnel as well as isotopic effects [3] and developing a phenomenology and interpretive ingredients down to the deep tunnelling regime [4-6]. Accurate data are becoming available for other reactions [7,8]. [1]V. Aquilanti, S. Cavalli, D. De Fazio, A. Volpi, A. Aguilar, J. M. Lucas " Benchmark rate constants by the hyperquantization algorithm. The F + H2 reaction for various potential energy surfaces: features of the entrance channel and of the transition state, and low temperature reactivity" Chem. Phys. 308, 237-253 (2005) [2] M. Tizniti, S. D. Le Picard, F. Lique, C. Berteloite, A. Canosa, M. H. Alexander, I. R. Sims "The rate of the F + H2 reaction at very low temperatures". Nature Chemistry., 6, 141-145 (2014) [3] D. De Fazio, V. Aquilanti, S. Cavalli, A. Aguilar, J. M. Lucas "Exact quantum calculations of the kinetic isotope effect: Cross sections and rate constants for the F + HD reaction and role of tunnelling" J.Chem. Phys. 125, 133109 (9 pages) (2006) [4] V. Aquilanti, K.C. Mundim, S. Cavalli, D. De Fazio, A. Aguilar, J. M. Lucas "Exact activation energies and phenomenological description of quantum tunneling for model potential energy surfaces. The F + H2 reaction at low temperature" Chemical Physics, 398,186-191 (2012) [5] V. H. C. Silva, V. Aquilanti, H. C. B. de Oliveira, K. C. Mundim "Uniform description of non-Arrhenius temperature dependence of reaction rates, and a heuristic criterion for quantum tunneling vs classical non-extensive distribution" Chem.Phys.Letters, 590, 201-207 (2013) [6] S. Cavalli, V. Aquilanti, K. C. Mundim, D De Fazio "Theoretical reaction kinetics astride the transition between moderate and deep tunneling regimes: the F + HD case", J Phys Chem A, 118, 6632-6641 (2014). [7] M. B. Krasilnikov, R. S. Popov, O. Roncero, D. De Fazio, S. Cavalli, V. Aquilanti, O. S. Vasyutinskii; "Polarization of molecular angular momentum in the chemical reactions Li+HF and F+HD" J. Chem. Phys. 138, 244302 (2013). [8] D. De Fazio, M. de Castro-Vitores, A. Aguado, V. Aquilanti, S. Cavalli " The He + H2+ -> HeH+ + H reaction: Ab initio studies of the potential energy surface, benchmark time-independent quantum dynamics in an extended energy range and comparison with experiments" J. Chem. Phys. 137, 244306 (2012)I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
