Slowing down of oxygen migration in the processes of radical oxidation and of phenanthrene phosphorescence quenching in methanol glasses at 90 K

Abstract

The hydroxymethyl radical oxidation kinetics follows the second-order equation with a time-dependent rate constant, K( t). The annealing effect is described by way of dividing K( t) into two factors, one of them depending on the preliminary annealing time (τ): K( t) = K 1( t + τ) K 2( t). The time dependence of both factors is fairly well approximated by the power functions: K 1( t + τ) ≈ ( t + τ) −0.18 and K 2( t ≈ t −0.26. The oxygen quenching of phenanthrene phosphorescence follows an exchange mechanism, with the static conditions setting in at 77 K. At 90 K oxygen diffusion adds to the quenching efficiency. The time of oxygen jumps (τ j) and its time dependence under the matrix annealing at 90 K are determined by comparing the theoretical 1/τ j dependence of the quenching volume with experiment. The 1/τ j(τ) is well described by the power function τ −0.18 ± 0.02). The annealing time functions of the oxidation rate constant and of the inverse jumping time are similar. The oxidation rate constant and the diffusion constant coincide in the order of magnitude. Consequently, the slowing down of oxygen migration contributes essentially to the time dependence of the rate constant.