Exploring the accuracy level of new potential energy surfaces for the F + HD reactions: from exact quantum rate constants to the state-to-state reaction dynamics

Abstract

Exact quantum reactive scattering calculations in the collision energy range 1-250 meV have been carried out for both the isotopic product channels of the title system. The dynamical studies compares an ab initio potential energy surface (PES) recently appeared in the literature (J. Chem. Phys., 2008, 129, 011103) with other phenomenological PESs. Vibrational branching ratios, cross sections and rate constants are presented and compared with molecular beam scattering experiments as well as with chemical kinetics data. In particular, the agreement of the vibrational branching ratios with experimental measurements is improved with respect to previous studies on other PESs, mainly because of the presence of a broad peak in the HF(v' = 3) integral cross section completely absent in the previous simulations. This feature, observed by molecular beam experiments, is the fingerprint of a new reaction mechanism operative in the dynamics described by the new PES. A conjecture for its origin, able to explain many of its characteristic aspects, is analyzed and discussed.

Dynamics of theS(D21)+HD(j=0Lara1, Chefdeville2, Hickson3 et al. 2012Phys. Rev. Lett.393290View full textAdd to dashboardCite

“…This is in sharp contrast to the F þ HD ! HF þ D reaction where the partial-wave resonances show up at more than 10-fold higher values in E T and E T , rendering them impossible to distinguish as resolved peaks in the ICSs of the crossed-beam experiments [30]. This explains why resonance features could be still discernable in our low-energy ICS measurements.…”

Complex angular momentum theory of state-to-state integral cross sections: resonance effects in the F + HD → HF(v′ = 3) + D reaction

“…was reported in ref. 64, where the authors followed some of the peaks in the reaction probability, thus approximating only the real parts of the corresponding CE trajectories, with the results 73 who were the first to discuss their effect on the J = 0 reaction probability of the F + H 2 system. We will continue to use the same nomenclature in what follows.…”

“…Finally, the physical mechanism of a resonance, e.g., capture in the van der Waals well of the exit channel, is most easily established for CE poles. 62,64 The resonance contributions to observable cross sections, on the other hand, are best described with the help of CAM trajectories. 42 Again, the ability to relate the two types of trajectories can be helpful.…”

“…As was mentioned in the Introduction, below we will use mostly the S matrix elements reported in ref. 64. However, to get an accuracy of about 1% in the modules and phases of the single state-to-state S-matrix elements, quantum reactive scattering calculations in the lower energy range were repeated using the improved code described in ref.…”

“…Availability of detailed experimental data prompted theoretical interest in the F + HD system, further encouraged by the fact that the ab initio potential energy surface (PES) obtained by Stark and Werner (SW) 53 was able to reproduce, at least qualitatively, some of the resonance features observed. 45 The SW PES was later modified in the entrance channel region, 54 in order to take into account the spin-orbit and the long-range interactions, 55 64 as the input data for our analysis of resonance effects in the title reaction. The purpose of this paper is, therefore, to perform a detailed analysis of the effects produced by quantum mechanical resonances in the HF(v 0 = 3)…”