Stereodynamic Effects of CO Molecules Scattered from a Graphite Surface

Abstract

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.

Scattering of N2 Molecules from Silica Surfaces: Effect of Polymorph and Surface Temperature

“…Recently, the need to include a proper formulation of the long-range attraction in the gas–surface interaction has been demonstrated, since it is promoting the formation of the precursor state that controls all basic elementary processes occurring at the gas–surface interphase [ 10 , 12 , 13 , 14 , 24 , 25 ]. Therefore, in the present study, we have evaluated the long-range interaction potentials, represented by the improved Lennard–Jones ILJ model [ 26 ], for N/N 2 impinging on quartz, inserted in the new PES formulation (see next Section 3.2 ), whilst the PES for the interaction of N/N 2 with cristobalite was lately determined in ref.…”

“…Several studies exist within this context, recently conducted by different groups, to characterize the inelastic scattering of molecules both with increasingly complex and refined experiments [ 1 , 2 , 3 , 4 , 5 , 6 ] and with state-resolved molecular dynamics (MD) simulations, the latter based on quantum [ 7 , 8 ], quasi-classical trajectory (QCT) [ 9 ] and semiclassical [ 10 , 11 , 12 , 13 , 14 ] methods.…”

“…These tasks will be carried out through MD simulations with the adoption of a semiclassical collision method [ 23 ] in conjunction with an accurate potential energy surface (PES) formulation, obtained by treating the interaction at short and long distances differently. Recently, it has been shown that long/intermediate-range interactions have a considerable impact on the microscopic dynamics of molecules interacting with surfaces [ 12 , 13 , 14 ]. Moreover, the appropriate treatment of the weak interactions is of primary importance to accurately describe the dynamics of several elementary processes, including those occurring at the gas–surface interphase, especially for molecules impinging at low collision energy [ 24 , 25 ].…”

“…[ 26 ] and already used in refs. [ 10 , 11 , 12 , 13 , 14 ], to study the dynamics of light molecules impinging on graphite. The obtained results are consistent with those of the molecular alignment processes, associated with the propensity and selectivity of elastic and inelastic scattering, observed in gas-phase experiments conducted with molecular beams [ 2 , 27 , 28 ].…”

The role of precursor states in the stereo-dynamics of elementary processes

“…[41][42][43] Potential energy surfaces, given in analytical form, have been used to investigate, by semi-classical molecular dynamics calculations, the scattering, under a variety of conditions of applied interest, of gaseous diatomic molecules, such as H 2 , O 2 , N 2 and CO in well-defined initial vibration-rotation (v i , j i ) states, from graphite surfaces. [44][45][46][47] The role of the precursor state, whose formation is controlled by the physisorption potential well arising from the long-range dispersion forces, has been properly emphasized. The collision dynamics, dominated by the coupling between translational and rotational internal degrees of freedom of molecule, indicates that, at low-medium collision energies, it can be also affected by the energy exchange with the surface phonons.…”