Investigation of CIDEP Effects of Hydrogen Radicals by Time Resolved ESR Spectroscopy

Abstract

By means of time resolved ESR spectroscopy the CIDEP effects of hydrogen radicals produced by pulse radiolysis of aqueous solutions were investigated. The quantitative analysis of the ESR time profiles of both H atom hfs lines and of D atom hfs lines based on the modified Bloch equations allows us to determine the spin relaxation times T1 and T2, the chemical life time τH and the initial and recombination polarizations PA, PA. While the relaxation rates T 1−1 and T 2−1 and the reciprocal of the life time τH−1 are proportional to the H radical concentration the recombination polarization PR is independent on the H atom concentration but shows an asymmetric behaviour to the spectrum centre. This asymmetry can be attributed to the ST0‐ and ST−1‐polarization of F pairs. – The experimental polarization parameters were compared with the theoretical results obtained from the stochastic Liouville equation by Pedersen and Freed. By this comparison the following quantities can be determined: The exchange interaction J(d) at the distance of closest approach of two H radical without recombination, The distance d of closest approach without use of the Smoluchowski relation and The number of radical pairs in the spur of water radiolysis including the probability of triplet and singlet precursors of direct produced H atoms in water radiolysis.