ESR Spectra Of Radical Pairs Research Articles

Spin coherence effects observed in the OD ESR spectra of radical pairs with strong hyperfine interaction

The optically detected ESR technique is used to record the spectra of a radical pair generated in the photolysis of 2,4,6-trimethylbenzoyl diphenylphosphine oxide in a micellar sodium dodecylsulfate solution. Along with the signals of the radicals of the pair, additional resonances have been detected in the spectrum, whose signal is inverted with respect to the fundamental ones. It is shown that the inverted lines consist of narrow and wide components, which arise from the effects of crossing and anticrossing of pair spin energy levels, respectively.

Theory of multiquantum optically detected ESR spectra of radical pairs. I. General theory. Resonances in parallel radio-frequency field

A general theory of multiquantum optically detected ESR spectra of radical pairs has been developed neglecting the processes of internal spin relaxation. The theory has been used to calculate multiquantum resonances in radiofrequency field which is parallel to the Zeeman field. The position and form of spectral components at arbitrary values of nuclear partner spins have been studied assuming a Poisson life-time-distribution of radical pairs. A physical interpretation of the results obtained has been proposed. The position of the spectral lines of a resolved spectrum for a complex nuclear structure of radical pair partners has been established.

Theory of multiquantum optically detected ESR spectra of radical pairs. II. Resonances in perpendicular radio-frequency field

The previously developed general theory of multiquantum optically detected ESR spectra of radical pairs has been used to analyse multiquantum resonances in the radiofrequency field that is perpendicular to the Zeeman field. The cases of circular polarization (resonance and nonresonance rotation directions) have been considered. The position and form of spectral components at arbitrary values of nuclear spins have been studied assuming the Poisson lifetime distribution of radical pairs. A physical interpretation of the results obtained has been proposed. The resonances of the partners with a complex nuclear structure have been discussed. The nonresonance corrections in the spectra studied have been analysed. A simple method for their estimation has been proposed.

CIDNP-detected ESR of radical pairs in the photolysis of quinones

CIDNP-detected ESR spectra of short-lived radical pairs in the photolysis of quinones ( p-benzoquinone and duroquinone) have been studied. The influence of the saturating rf-field amplitude on the ESR spectra of radical pairs detected by this method has been demonstrated and investigated.

Ion—molecular charge transfer as studied by the method of optically detected ESR of radical pairs

Abstract Effects of ion—molecular charge transfer upon optically detected (OD) ESR spectra of radical pairs have been studied experimentally and theoretically. Theoretical analysis has shown that under certain conditions (often realized in experiments) OD ESR spectra are analogous to standard ESR ones. Broadening and collapse of the hyperfine structure (exchange broadening) have been observed experimentally depending on the concentration of neutral acceptors. Ion—molecular charge transfer rate constants have been calculated for some radical-anions from the experimental data.

Mechanism of hydrogen atom transfer in the photoexcitation of sterically hindered quinones and phenols

1. Analysis of the angular dependence of the ESR spectra of radical pairs formed under irradiation with polarized light showed the momentum vector for electron transfer from 3,6-ditert-butyl-o-benzoquinone to be directed at the angle of 70 ± 5° with respect to the plane of the molecule. 2. In frozen Vaseline solution, a triplet-triplet mechanism of energy transfer from 3,6-ditert-butyl-o-benzoquinone to 2,4,6-tri-tert-butylphenol is ineffective. 3. We have proposed a phototransfer mechanism in which the H atom is detached from the phenol molecule by a quinone molecule which is, itself, in a singlet excited state. Although it is clear that there is no isotope effect in phototransfer, it is equally clear that such an effect will come into play in the reverse process. The magnitude of this effect has been estimated from an analysis of the equation for the photoyield of radical pairs.

ESR spectra of radical pairs in irradiated oriented polyethylene

ESR spectra of radical pairs in irradiated oriented polyethylene