[en] The technique of spin trapping with nitrone spin traps gained wide acceptance as a method for estimating OH yields in ESR studies. Fast optical kinetic techniques applied to a series of these traps are reported to reveal relaxation spectra that indicate two absorption maxima with different time constants showing second order behaviour in most cases. These two spectral regions show different kinetics. Thus, two reaction sites are indicated, only one of which is necessarily a measure of initial OH when ESR methods are used. One other trap (DMPO) decays after OH reaction in one mode suggesting that its final product might be useful as a measure of initial OH. The ESR evidence also shows that OH detection can be improved significantly by spin trapping α-hydroxyalkyl radicals formed by OH attack on alcohols. (author)