Events
NON-MARKOVIAN IONISATION AND RADICAL-IONS RECOMBINATION AFFECTED BY DIFFUSION AND SPIN-CONVERSION
Diffusion assisted transfer reactions in liquid solutions were first shown to be non-Markovian by Smoluchowski (1917) who
proved that their rate constants are time dependent under
diffusion control. This approach was developed into Differential
Encounter Theory (DET) at late 60-th when the way was found how to calculate the time dependent rate constant of bimolecular reactions from the first quantum-mechanical principles. Fitted to experiment- ally studied transient effects in ionization DET provides us with the reliable data on electron tunneling length and coupling. The Radical Ion Pairs (RIP) produced by ionization are subjected to geminate recombination and separation which is usually considered independently assuming arbitrary initial separation between ions. Only the Unified Theory (UT) developed in 1992 joined together the intimately associated bimolecular ionization and geminate recombi- nation from either singlet or triplet states, accounting for the incoherent spin-conversion between them. The theory fits well the kinetics of RIP accumulation/dissipation and explains the non- monotonous diffusional dependence of the quantum yields of free ions and triplet recombination products provided the recombination is not contact and spin-conversion during encounter is rather strong. In contact approximation of recombination the same yields were exactly calculated using the coherent (Hamiltonian) descript- ion of spin-conversion carried out by HFI and delta-g mechanisms. In the latter case the Magnetic Field Effect is well fitted, but only with coherent conversion. Nevertheless, the incoherent (rate) description of spin-conversion was shown to be surprisingly good
in zero magnetic field. The UT of the highly exergonic non-
contact quenching of Perylene by TCNE was successfully fitted to the whole kinetics of ionization via double channel electron transfer (to the ground and excited states of charged products) as well as to Stern-Volmer constant at any concentration. The kinetic rate constants of both channels were shown to be much larger than the latter which appears to be a diffusional one. This fact resolves the famous Rehm-Weller paradox without revision the Marcus Free Energy Gap law.