Benchmarking chemical reactivity in the deep tunnelling regime: the ultra-cold behaviours of the F+H2 reactive system and its isotopic variants

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 [1]. 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 [2], recently validated by experiments in the moderate tunnelling regime [3]. The F+ HD variant permits exploring tunnel as well as isotopic effects [4] and developing a phenomenology and interpretive ingredients down to the deep tunnelling regime [5,6] where the reactivity is strongly dominated by resonances and quantum effects. In the conference we discuss and compare cold and ultra-cold reactive behaviours of the F+H2 reaction and of its isotopic variants (F+HD and F+D2) to deeply understand its dependence by the entrance channel behaviour of the potential energy surface [2]- Simplified dynamical treatments and ultra-cold theories will be employed to understand the various resonance features obtained by 'exact' quantum reactive scattering results and as they affect cross sections and kinetic behaviours. [1] D. De Fazio, S. Cavalli and V. Aquilanti ; J. Phys. Chem. A, 120 (2016) 5288. [2] V. Aquilanti, S. Cavalli, D. De Fazio, A. Volpi, A. Aguilar, J. M. Lucas; Chem. Phys. 308, 237 (2005) [3] M. Tizniti, S. D. Le Picard, F. Lique, C. Berteloite, A. Canosa, M. H. Alexander, I. R. Sims Nature Chemistry., 6, 141 (2014) [4] D. De Fazio, V. Aquilanti, S. Cavalli, A. Aguilar, J. M. Lucas; J.Chem. Phys. 125, 133109 (2006) [5] V. Aquilanti, K.C. Mundim, S. Cavalli, D. De Fazio, A. Aguilar, J. M. Lucas Chemical Physics, 398,186-191 (2012) [6] S. Cavalli, V. Aquilanti, K. C. Mundim, D De Fazio; J Phys Chem A, 118, 6632-6641 (2014).