AM1 CALCULATIONS ON REACTIVE OXYGEN SPECIES .1. ANALYSIS OF HYDROXYL RADICAL REACTIONS

A variety of hydroxyl-radical reactions (hydrogen abstraction, (OH)-O- . addition to unsaturated molecules, and decomposition of the radical adducts) has been investigated by means of the AM1 semiempirical molec ular-orbital method. A limited CI treatment was employed to explore th e doubler ground-state potential surface of each reaction. The analysi s focuses on energy barriers of the reactions and the temperature depe ndence of the pre-exponential term in the expression for the rate cons tant. Experimental values of the Arrhenius activation energy E(a) and the heat of reaction Delta H-f300(o) are compared with the results of the calculations. Although the AMI method generally exaggerates the he ight of energy barriers and the stability of radical reaction products , trends in E(a) and Delta H-f300(o) are qualitatively followed by the calculations. To quantify the relationship between E(a) and the calcu lated AM1 barrier Delta H-f(double dagger), the data obtained from 19 reactions were subjected to linear regression analysis. The resultant expression yields useful estimates of E(a) from computed values of Del ta H-f(double dagger).