TY - JOUR

T1 - General relationships between the kinetic characteristics of bulk and geminate recombination of radicals in solutions

AU - Doktorov, Alexander B.

AU - Lukzen, Nikita N.

N1 - D.A.B. (Voevodsky Institute of Chemical Kinetics and Combustion SB RAS) acknowledge the core funding from the Russian Federal Ministry of Science and Higher Education (FWGF-2021-0002); N.N.L (International Tomography Center) acknowledge funding from Russian Federal Ministry of Science and Higher Education of the Russian Federation (Contract No. 075-15-2021-580).

PY - 2024/2

Y1 - 2024/2

N2 - Based on the (differential) Encounter theory developed in the literature, which describes the change in the internal quantum states of particles encountered in liquid dilute solutions due to stochastic (diffusion) molecular motion, closed kinetic equations for the temporal change in the concentration of free radicals recombining at encounters were obtained. The recombination rates from singlet and triplet states are often different, the recombination products from these states may also be different, i.e., the recombination process is spin-selective. The radical spins experience any quantum spin interactions including Zeeman interaction with external magnetic fields and hyperfine couplings with magnetic nuclei and the processes of longitudinal and transverse spin relaxation. In general, recombination can occur both from singlet and triplet states. The rates of such recombination are not limited by the traditional contact model, implying that recombination occurs only at the radicals contact, and, like any spin interactions, are not assumed to be spherically symmetric. Under these general conditions, an unambiguous relationship has been established between the bulk recombination rate constant and the recombination yields of the corresponding geminate reaction from the singlet and triplet states. In the particular case of the same spatial dependence of the rates of singlet and triplet recombination, the rate constant can be expressed only through the singlet recombination yield for a singlet precursor or through the triplet recombination yield for a triplet precursor, despite the fact that recombination occurs from both spin states. The particular case of spherically symmetric recombination probability of the freely diffusing radical pairs in liquid solution, which is the most common one in the literature, is also considered.

AB - Based on the (differential) Encounter theory developed in the literature, which describes the change in the internal quantum states of particles encountered in liquid dilute solutions due to stochastic (diffusion) molecular motion, closed kinetic equations for the temporal change in the concentration of free radicals recombining at encounters were obtained. The recombination rates from singlet and triplet states are often different, the recombination products from these states may also be different, i.e., the recombination process is spin-selective. The radical spins experience any quantum spin interactions including Zeeman interaction with external magnetic fields and hyperfine couplings with magnetic nuclei and the processes of longitudinal and transverse spin relaxation. In general, recombination can occur both from singlet and triplet states. The rates of such recombination are not limited by the traditional contact model, implying that recombination occurs only at the radicals contact, and, like any spin interactions, are not assumed to be spherically symmetric. Under these general conditions, an unambiguous relationship has been established between the bulk recombination rate constant and the recombination yields of the corresponding geminate reaction from the singlet and triplet states. In the particular case of the same spatial dependence of the rates of singlet and triplet recombination, the rate constant can be expressed only through the singlet recombination yield for a singlet precursor or through the triplet recombination yield for a triplet precursor, despite the fact that recombination occurs from both spin states. The particular case of spherically symmetric recombination probability of the freely diffusing radical pairs in liquid solution, which is the most common one in the literature, is also considered.

KW - Bulk recombination of free radicals

KW - Diffusion-influenced reactions

KW - Recombination rate constant

KW - Singlet and triplet precursors

KW - Singlet and triplet recombination yields

UR - https://www.scopus.com/record/display.uri?eid=2-s2.0-85178207450&origin=inward&txGid=2fa6c7004bd781f969368dc398fcf61e

UR - https://www.mendeley.com/catalogue/aa7a2cb9-5e35-3e17-af2b-bd05e25ed7fe/

U2 - 10.1007/s10910-023-01550-z

DO - 10.1007/s10910-023-01550-z

M3 - Article

VL - 62

SP - 502

EP - 521

JO - Journal of Mathematical Chemistry

JF - Journal of Mathematical Chemistry

SN - 0259-9791

IS - 2

ER -