Theoretical modeling of photodissociation dynamics of CH3I on MgO(001)

Abstract

The 257 nm photodissociation dynamics of CH3I adsorbed on a MgO(001) surface is studied using classical molecular dynamics method. The substrate is modeled by a 6×6×3 slab of movable ions surrounded by a semi-infinite array of static ions. A single adsorbate molecule is aligned with the surface normal, the methyl end pointed either toward or away from the substrate. The system is equilibrated by using a Monte Carlo method to obtain the starting configuration. Fragment final state distributions are calculated for kinetic energy, angle of departure, and rovibrational states. Upon photodissociation of the adsorbate with the methyl end pointed toward the surface, the methyl fragments experienced vibrational cooling, in agreement with experimental results. Some rotational excitation is predicted for fragments produced from the methyl down orientation. The kinetic energy distributions of both the methyl and iodine fragments are qualitatively similar to those obtained by experiment. The results are compared with those obtained by the same model for CH3I adsorbed on LiF(001). Trapping of iodine atoms by the surface has also been investigated in this simulation.

Mixed quantum/classical simulation of the photolysis of HCl on MgO(001)

“…The large number of degrees of freedom made the studies focus predominantly on two situations. One is to use classical molecular dynamics, [1][2][3][4] which can be done with relative ease also in systems with a large number of coordinates. On the other hand, quantum calculations for the photofragments must rely on more stringent dynamical approximations like the one of a rigid surface.…”

Photoinitiated Reaction Dynamics between Aligned Adsorbates on Solid Surfaces: A Theoretical Exploration of the H + CO2System on LiF(001)

“…The energy distribution for the bromine atom (lower panel in Figure ) displays a high-energy tail, which is consistent with such a mechanism. Similar events in surface photodissociation have been discussed extensively before. − ,− Hydrogen atoms undergoing such chattering would likely become unavailable for reaction during subsequent encounters with coadsorbed CO 2 , both due to the energy loss and the angle of departure.…”

“…Similar events in surface photodissociation have been discussed extensively before. [47][48][49][55][56][57][58] Hydrogen atoms undergoing such chattering would likely become unavailable for reaction during subsequent encounters with coadsorbed CO 2 , both due to the energy loss and the angle of departure.…”

“…The simulation is carried out in two steps, similar to previous quasi-classical trajectory studies of photodissociation of adsorbates on insulator surfaces. ,− First, the adsorbates are equilibrated at a given temperature (typically 80 K) using the Metropolis Monte Carlo (MC) method . In the MC simulation, the molecules are treated as rigid skeletons, and both the center of mass and the orientation of the molecules with respect to the surface are varied randomly in search of an energy minimum.…”

Extended BEG model of monhalogenated methanes physisorbed on ionic crystals

“…Binding energy asymmetry is estimated to arise from asymmetric dipole-substrate interactions ( Table 2). [34][35][36][37] Depending on dipole orientation, the induced dipole will reinforce or mitigate the binding energy by an amount that is proportional to the square of the induced dipole moment and inversely proportional to the molecular polarizability α, i.e, ε up/down = ε b ± [p ind 2 /2⋅α]; this contribution is calculated and tallied in Table 2. The adsorbate-substrate field strength parameters ∆ and H are then calculated directly from Eq.…”