Kinetic study of the forward and backward electron transfer between N,N,N′,N′-tetramethylbenzidine and CH2Cl2 in solid argon leading to a photoequilibrium Original Research Article

The kinetics of the two-photon ionization of N,N,N′,N′-tetramethylbenzidine (TMB) in dichloromethane (CH2Cl2)-doped solid argon using 254 nm high-pressure Hg-lamp radiation is investigated by means of UV/VIS absorption spectroscopy. The experimental findings, especially the incomplete running of the ionization reaction, can be quantitatively understood on the basis of a kinetic model which includes dissociative electron attachment to CH2Cl2 and associative photodetachment of the corresponding radical anion. The model implies that the underlying electron transfer reactions reach the photoequilibrium TMB+CH2Cl2⇌hν2hνTMB•++ClHCH•⋯Cl−. The ionization cross-section of TMB in the lowest triplet state, the cross-section of associative photodetachment and the rate constant of cation electron recombination are obtained by adapting calculated to measured irradiation time dependent concentrations of the radical cation.