The kinetics of associative desorption from mixed adlayers containing two kinds of particles (N and 0) have been examined. Standard statistical mechanical methods have been employed to study the effects of lateral interactions (ω
NN
, ω
NO
, ω
OO
) between near-neighbour particles on the desorption kinetics while the adlayer stoichiometry varies continuously during a desorption sweep. Although the most general case ω
NN
≠ ω
NO
≠ ω
OO
≠ 0) is found to be mathematically intractable, either one of two useful approximations can lead to analytic expressions for the desorption rate of N
2
, NO and O
2
. Both of these approximations have been used to simulate the thermal desorption spectra from a 1:1 layer of N and O atoms absorbed on Pt, Ni and Ru surfaces. The results show that, although the operation of lateral interactions can profoundly affect the desorption kinetics of these systems they cannot significantly alter the product distribution. N
2
and O
2
are overwhelmingly the major products, with NO desorption being entirely negligible in every case. We therefore conclude that observations of molecular NO in thermal desorption in these systems is evidence of molecularly adsorbed NO on the surface. Such desorption of NO is
not
due to recombination of surface N and O atoms. Reasonable values of the interaction parameters are used in model calculations which give a fairly good quantitative account of the available experimental data. The comparison with experiment leads to the conclusion that O-O repulsions are significant in every case. The N-N interaction is either zero or slightly attractive on Pt and Ni, but is very definitely repulsive on Ru.
Lateral interactions between adsorbed molecules: Investigations of CO on Ru(001) using nonlinear surface vibrational spectroscopies
