Alkaline 2'-deoxyguanosine undergoes one- and two-photon laser photoionization at 266 nm. Similar to tryptophan and indole, the one-photon quantum yield increases five-fold between 296 and 362 K. Earlier Arrhenius analyses of tryptophan and indole photoionization rate constants, yielded unreasonably large pre-exponential factors (10(13)-10(18) s(-1)). An analysis employing pre-exponential factors for diffusion controlled reactions (10(10)-10(11) s(-1)) provides evidence of activation barriers that decrease with increasing temperature over a range where water structure undergoes significant changes. In the context of Marcus theory, this analysis suggests that curvatures of the electron-transfer free energy surfaces decrease as temperature increases.