Reaching the cold regime: S(1D) + H2 and the role of long-range interactions in open shell reactive collisions

Abstract

Reactive cross-sections for the collision of open shell S( 1 D) atoms with ortho-and para-hydrogen, in the kinetic energy range 1−120 K, have been calculated using the hyperspherical quantum reactive scattering method developed by Launay et al. [Chem. Phys. Lett. 169, 473 (1990)]. Short-range interactions, described using the ab initio potential energy surface by Ho et al., were complemented with an accurate description of the longrange interactions, where the main electrostatic (∼ R −5 ) and dispersion (∼ R −6 ) contributions were considered. This allows the comparison with recent experimental measurements of rate constants and excitation functions for the title reaction at low temperatures [Berteloite et al., accepted in Phys. Rev. Lett., 2010]. The agreement is fairly good. The behavior in the considered energy range can be understood on the average in terms of a classical Langevin (capture) model, where the centrifugal barriers determine the amount of reactive flux which reaches the barrierless transition state. Additionally, the structure of the van der Waals well provides temporal trapping at short distances thus allowing the system to find its way to the reaction at some classically-forbidden energies. Interestingly, the cross-section for para-hydrogen shows clearly oscillating features associated to the opening of new partial waves and to shape resonances which may be amenable to experimental detection.

Dynamics of theS(D21)+HD(j=0Lara1, Chefdeville2, Hickson3 et al. 2012Phys. Rev. Lett.Self Cite413290View full textAdd to dashboardCite

“…3) associated with the PES of Ho et al These potentials have been calculated by adiabatically separating the fast coordinates, r and , from the collision coordinate R [where (R, r, ) are the usual reactant Jacobi coordinates]. All the terms in the Hamiltonian, except for the radial collision kinetic energy, were diagonalized in a basis of reactant states for a fixed R [21]. Interestingly, the resulting average over internuclear distances and angles of approach displays in general two barriers as a function of R: the outer barrier is the usual centrifugal one; however, the very sharp inner one seems to be a feature of the system, appearing for many different partial waves and on both 1 A 0 PESs considered.…”

“…The TI QM calculations were performed by applying the hyperspherical quantum reaction scattering methodology, using the ab initio ground-state 1 A 0 PES calculated by Ho et al [20], which was complemented with accurate calculations of the long-range interactions [21]. Converged cross sections were obtained on a fine grid up to E T ¼ 5 meV (partial waves J ¼ 0-16) and then on a coarser grid up to E T ¼ 28:5 meV (partial waves J ¼ 0-25), due to computational time increasing excessively with J.…”

Rate coefficients from quantum and quasi-classical cumulative reaction probabilities for the S(1D) + H2 reaction

“…56 Recent modifications of the method, performed in order to allow the accurate inclusion of long-range interactions, were described in depth in Ref. 45 in the context of our study of the title reaction at low collision energies. Such modifications are not necessary in the present work.…”

The Influence of Collision Energy on the Reaction H+HS→H2+S

“…The system of S+H 2 has been studied in both theoretical [1][2][3][4][5][6][7][8][9] and experimental 10,11 methods due to its important role in combustion and atmospheric chemistry. Maiti et al 4 have studied the intersystem crossing effect in the reaction S+H 2 by employing a "mixed" representation approach in conjunction with a trajectory surface-hopping method.…”

“…In the study of Berteloite et al, 7 kinetics and crossed-beam experiments were performed in experimental conditions approaching the cold energy regime. By employing the quantum mechanical (QM) hyperspherical reactive scattering method and quasi-classical trajectory (QCT) and statistical quasi-classical trajectory (SQCT) approaches, Lara et al 8 have calculated the reaction probabilities as a function of total angular momentum (opacity function) and the resulting reaction cross-section for the reaction S+H 2 at low energies (0.09-10 meV) based on two different ab initio potential energy surfaces (PESs). S. H. Lee and Liu 10,11 have investigated the S( The inverse reaction H+HS has also attracted the attentions.…”