Selectivity in the inelastic rotational scattering of D 2 and HD molecules from graphite: Similarities and differences respect to the H 2 case

2020

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The scattering of N2 molecules from a graphite surface was studied using molecular dynamics simulations based on a state-to-state semiclassical collisional method in conjunction with a new reactive potential energy surface that includes the long-range part describing properly, for all accessible molecular configurations with respect to the surface, the noncovalent interactions promoting the physisorption. Molecules in well-defined initial internal vibrational and rotational states (v i , j i ) impinge on the surface with collisional energy (E coll) covering the range from thermal (0.01 eV) up to hyperthermal values (2.0 eV). In addition to the ground state of ortho and para symmetry, nitrogen molecules excited initially in low-medium v i and j i levels have been also considered. The main features of scattering dynamics, already reported in the literature, are confirmed on a larger range of both initial rotational levels and collision energies. However, new selectivity and stereodynamics effects are highlighted by studying in detail the microscopic mechanisms driven by the interaction that promotes physisorption. This investigation contributes also to a broader understanding of molecular scattering from surfaces by relating observed effects to phenomena controlled by rotational alignment and rotational rainbow, already well-characterized both experimentally and theoretically, in gas phase collisions and for molecular scattering from metallic surfaces.

Section: Computational Detailsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Selectivity and Stereodynamics Effects in the Scattering of Nitrogen Molecules from a Graphite Surface

2020

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“…In two recent papers, , we simulated the interaction of H 2 , HD, and D 2 molecules, in well-defined initial roto–vibrational ( v i , j i ) states, with a graphite surface. The investigation was conducted by using molecular dynamics (MD) calculations, on the basis of a PES, formulated in terms of a recently proposed improved Lennard Jones (ILJ) model, suitable to describe noncovalent long-range interactions in the full space of the relative configurations.…”

Section: Introductionmentioning

confidence: 99%

On the Influence of Rotational Motion of Oxygen Molecules on the Scattering from Graphite Surfaces

2019

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A new analytical potential energy surface is proposed to investigate, by semiclassical molecular dynamics calculations, the scattering of O 2 molecules in well-defined initial roto−vibrational (v i , j i ) states from graphite under a variety of conditions of applied interest. The reaction dynamics appears to be dominated by the coupling between translational and rotational internal degrees of freedom of molecule, that, at low-medium collision energies, can be also triggered by the energy exchange with the surface phonons. The final states (v f , j f ) of backscattered molecules are characterized and carefully analyzed. Most important results are the following:(1) after the interaction with the surface, molecules are backscattered mainly in a direction very close to the specular one; (2) v i is preserved, except for high initial vibrational states; (3) the surface temperature plays a minor role; and (4) the final j f states exhibit non-Boltzmann distributions with the main peak nearby j f = j i and a secondary maximum at very high j f . Moreover, the features of rotational distributions suggest a close correlation between the initial rotational configuration of impinging molecules and the final state achieved after the scattering. These findings, complementary to those from molecular beam experiments, cast light on relevant selectivities in elastic and inelastic collision events that control the stereodynamics of several elementary processes occurring both in gaseous and condensed phases for low energy (as those meet in the interstellar medium) as well as for high energy (as those of interest for aerospace applications).

“…For this reason, we have undertaken the study of the interaction of light molecules, with well-defined internal energy, with a graphite surface. In the previous investigations − some selectivity and peculiarities, together with stereodynamic effects, have been pointed out for H 2 (and its isotopologue molecules), O 2 , and N 2 molecules using chemical molecular dynamics (MD) simulations in conjunction with an accurate formulation of the interaction potential energy surface (PES), which drives the collision dynamics. In particular, the adopted formulation exploits an improved Lennard-Jones (ILJ) model that represents the long-range interaction, playing a key role in the trapping of gaseous molecules on surfaces, with a high degree of accuracy based on the intrinsic physical properties of interacting species.…”

Section: Introductionmentioning

confidence: 99%

Stereodynamic Effects of CO Molecules Scattered from a Graphite Surface

2021

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The scattering of CO molecules from a graphite surface has been characterized by exploiting molecular dynamics simulations, based on a chemical state-to-state semiclassical collisional method, and adopting a new reactive potential energy surface that considers the proper treatment of long-range noncovalent interactions promoting the physisorption. Carbon monoxide molecules impinge the surface in well-defined initial rotovibrational states and with the collision energy varying from subthermal up to hyperthermal values. The simulations predict that scattering events occur through both single- and multi-bounces and the initial vibrational state is preserved. In the multibounces instance, molecules tend to be trapped in the physisorption well, especially for collision energies lower than the thermal one. For medium–high collision energies, the scattering occurs mainly via a single-bounce mechanism. The heteronuclear character of the molecule brings out a new intriguing stereodynamic effect, in addition to those highlighted for homonuclear molecules: due to the anisotropic physisorption attraction, the molecule C-end bends toward the surface while approaching this latter. This effect produces evident propensities in the final rotational distributions of the CO scattered molecules.