Classical stereodynamics in Ar + NO inelastic collisions

Abstract

The stereodynamics of the Ar þ NO (j ¼ 0) rotational inelastic excitation has been investigated at 66 meV by means of quasiclassical trajectories on a recent ab initio potential energy surface. A marked correlation between the preferred sense of rotation of NO and the scattering plane is obtained for the highest rotational levels accessible, which are excited in strong repulsive collisions. This result is in qualitative agreement with recent quantum mechanical calculations and experimental measurements. For the lower rotational levels, where the interactions are not so repulsive, the preferred sense of rotation is found to oscillate with scattering angle, but the intensity of the oscillations is small and their angular range is not entirely coincident with those from quantum mechanics and experiment. Classical dynamics, even including attractive interactions, cannot account properly for the mentioned oscillatory behaviour. Secondary encounters between the outgoing Ar atom and NO molecule, giving rise to 'chattering', are found to be relatively frequent, leading to a decrease in the final rotational energy of NO with respect to that attained in the first encounter. Chattering trajectories are defined and their mechanism is characterized. w Electronic supplementary information (ESI) available: Fig. 3 in colour. See

Rotational alignment effects in NO(X) + Ar inelastic collisions: A theoretical study

“…As noted in a previous QCT study of NO(X) + Ar, 17 if a great amount of linear momentum is transferred to the rotational degrees of freedom of the molecule, so that the atom slows down, a secondary, so-called chattering, collision can occur by which the degree of rotational excitation can be reduced. 15,17,33 The result of this cooling is that the population of high rotational states of NO(X) after collision is reduced. Note that the HEHS model does not predict any significant chattering when the correct dimensions of the ellipsoid are employed.…”

“…14,15 Early theoretical work by Alexander established propensity rules for the QM cross sections involving magnetic level, m j , resolved transitions for NO(X) + Ar. 16 Rotational polarization effects have also been investigated using quasiclassical trajectory (QCT) methods by Aoiz et al 17 These calculations were performed on the V sum PES, and their results reproduced well the quantum mechanical ones, once the latter were averaged over the initial, and summed over the final -doublet states. The authors also looked at the role of chattering collisions in rotationally inelastic scattering in this system.…”

“…The authors also looked at the role of chattering collisions in rotationally inelastic scattering in this system. 17 They provided a definition of chattering en-counters, and showed that, while chattering collisions do play some role in NO(X) + Ar in cooling the final rotational excitation compared with non-chattering collisions, they tend to result in lower angular momentum polarization than nonchattering collisions. 17 In a recent theoretical study of NO(X) scattering by the rare gases, Lemeshko et al 18 have described the alignment effects in the forward scattered region in terms of a Fraunhofer diffraction model.…”

“…17 They provided a definition of chattering en-counters, and showed that, while chattering collisions do play some role in NO(X) + Ar in cooling the final rotational excitation compared with non-chattering collisions, they tend to result in lower angular momentum polarization than nonchattering collisions. 17 In a recent theoretical study of NO(X) scattering by the rare gases, Lemeshko et al 18 have described the alignment effects in the forward scattered region in terms of a Fraunhofer diffraction model. This model accurately describes the oscillatory rotational alignment in the extreme forward scattered region, where diffraction effects dominate, but says little about the rotational polarization in the sideways and backward directions.…”

A quasiclassical trajectory analysis of stereodynamics of the H + FCl (v = 0 – 3, j = 0 – 3) → HCl + F reaction

“…34 Subsequently, the QCT procedure was gradually developed and optimized to study the chemical stereodynamics to other reaction system. [29][30][31][32][33] Many other theoretical methods were also developed to study the chemical stereodynamics, and the excellent work has been done by Aquilanti and co-workers, 35, 36 Aoiz and co-workers, 37,38 Roncero and co-workers and BalintKurti and co-workers. [39][40][41][42][43] …”