J. Gislason et H. Sellers, MOLECULAR-DYNAMICS SIMULATIONS OF REACTIONS ON METAL-SURFACES - RATE CONSTANTS FOR SELECTED DIATOMIC DISSOCIATION REACTIONS, Surface science, 385(1), 1997, pp. 77-86
We have employed our normalized bond index (NBI) potential energy func
tion in molecular dynamics simulations of the dissociation of various
isotopes of (a) O-2 on Ag(111), Au(111), Pt(111) and Ni(111), (b) S-2
on Ni(111), and (c) C-2 on Ni(111) surfaces for the purpose of computi
ng the zero coverage limit Arrhenius reaction rate constants. For O-16
(2) on Pt(111) we repeated the rate constant calculations at a simulat
ed coverage of 0.4, in order to compare our result with an experimenta
l value that corresponds to a low but otherwise unknown coverage. Our
computed rate constants for O-16(2) dissociation on Pt(111) are: (a) f
or the zero coverage limit, k = 5.42 x 10(12) s(-1) exp {-1.1 kcal/mol
/RT}, (b) for moderate coverage, k = 7.43 x 10(11) s(-1) exp {-5.8 kca
l/mol/RT}. The experimentally determined rate constant 9 x 10(11) s(-1
) exp {-2.5 kcal/mol/RT} is bracketed by our calculated values. Our co
mputed rate constants possess the general trend that the Arrhenius pre
-exponentials decrease with increasing vibrational mass of the dissoci
ating bond. Also, the Arrhenius pre-exponentials tend to decrease with
decreasing atomic heat of adsorption. We emphasize that the Arrhenius
activation barrier is an effective barrier that depends on several as
pects of the system, and may not closely correspond with any single fe
ature of the potential energy surface. (C) 1997 Elsevier Science B.V.