Njb. Green et al., SPIN EFFECTS AN SPUR KINETICS - REENCOUNTERS AND THE INDEPENDENT PAIRS APPROXIMATION, Journal of the Chemical Society. Faraday transactions, 91(2), 1995, pp. 223-229
Citations number
41
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
Recent developments in the theory of reaction kinetics in multi-pair s
purs have incorporated the possibility that spin correlations may affe
ct the chemistry in a complex manner. The analyses published so far ha
ve employed two distinct approximations: that pairs evolve independent
ly, except on encounter, and that a non-reactive (e.g. triplet) encoun
ter does not affect the subsequent encounter rates. This paper present
s tests of these two approximations, both separately and in combinatio
n, using two Monte Carte simulation techniques: a random-flights metho
d, in which spin effects can be incorporated without either approximat
ion, and a modification of the independent reaction times method, whic
h is subject to the independent pairs approximation, but treats reenco
unters properly. The accuracy of both approximations is assessed, sepa
rately and in combination; both result in small errors in opposite dir
ections. As a result of this cancellation the predictions of random-fl
ights simulations and the master equation model, where both approximat
ions are used in combination, agree to within 2%. This error is consid
erably smaller than the spin effects under investigation, and is also
much smaller than errors incurred by using either (i) the prescribed d
iffusion approximation for the encounter rate coefficient (rather than
the independent pairs approximation) or (ii) a deterministic diffusio
n-kinetic analysis of the spur chemistry employing a macroscopic react
ion rate coefficient without explicit consideration of spin correlatio
n effects.