Comparison of exciplex generation under optical and X-ray excitation.

Exciplex generation under optical and X-ray excitation in identical conditions is experimentally compared using a specially chosen model donor-acceptor system, anthracene (electron acceptor) and N,N-dimethylaniline (electron donor) in non-polar solution, and the results are analyzed and interpreted based on analytically calculated luminescence quantum yields. Calculations are performed on the basis of kinetic equations for multistage schemes of bulk exciplex production reaction under optical excitation and combination of bulk and geminate reactions of radical ion pairs under X-ray excitation. These results explain the earlier experimentally found difference in the ratio of the quantum yields of exciplexes and excited electron acceptors (exciplex generation efficiency) and the corresponding change in the exciplex generation efficiency under X-irradiation as compared to the reaction under optical excitation.

Bifurcation transitions in a photochemical system under low magnetic fields.

In the last decades, the effect of low magnetic fields on biochemical and chemical systems has been an urgent problem. By now numerous experimental and theoretical studies have been conducted to demonstrate that commonly this effect is of no essence as it does not exceed 10%. However, there are experimental works which testify that in some systems, magnetic field effects are more significant. Thus, of great interest is an active search for rather simple but realistic models that are based on physically explicit assumptions and able to account for a strong effect of low magnetic fields. The present work not only offers a theoretical study on the simplest photochemical system, describing a reversible reaction of photodissociation, but also shows how a low magnetic field can strongly modify its properties under highly nonequilibrium conditions. It is assumed that external magnetic field can have effect on the rates of radical reactions occurring in a system. This, in turn, leads to bifurcation of the nonequilibrium stationary state and, thus, to a drastic change in the properties of chemical systems (temperature and reagent concentration).

The possibility of regime changing in chain reactions with degenerate branching under the influence of external magnetic field.

A reaction of hydrocarbons oxidation in the liquid phase is treated theoretically. The reaction system under discussion is a flow reactor, to the inlet of which the hydrocarbon is constantly delivered in the mixture with an inhibitor under oxygen saturation conditions; the reaction mixture constantly flows from the chamber at the same rate. The reaction gives rise to radicals that can subsequently recombine. It is shown that under certain conditions in this reaction system, three steady states may arise, two of which are stable and the third state is unstable. By varying rate constants of radical reactions by means of an external magnetic field, one can disturb the steady state stability and transfer the system to another steady state, which will be accompanied by an abrupt change in the concentration of reacting substances.

General kinetic laws of monomolecular-bimolecular reaction A+B <= => C in solutions.

Non-Markovian kinetic equations of the reversible monomolecular-bimolecular reactions of the type A+B right arrow over left arrow C (at arbitrary ratio between A and B concentrations) derived earlier are used in the calculation of kinetics on macroscopic space-time scales. It is found that the kinetics of the systems with different structure of reactants is universal, and it is the direct generalization of the kinetic law of mass action of formal chemical kinetics. The analysis of the kinetics allows one to establish the time range of the applicability of the law of mass action. It is shown that beyond these limits the usual kinetic law of mass action becomes invalid, and correct description of the kinetics even in the most rough approximation calls for the non-Markovian corrections to usual kinetic laws.