Specific MARY spectrum from radical anion of pentafluorobenzene

Abstract

The paper presents the first resolved experimental magnetically affected reaction yield (MARY) spectrum for a system with nonequivalent nuclei, radical anion of pentafluorobenzene. This observation dispels the common apprehension that because of a rather involved energy level layout a system with not all nuclei magnetically equivalent cannot produce resolved MARY lines in nonzero fields, and greatly increases the practical scope of level-crossing techniques for studies of spin-correlated radical pairs. The experimental finding is supported by schemes of energy levels calculated for this system.

Determination of Hyperfine Coupling Constants of Fluorinated Diphenylacetylene Radical Anions by Magnetic Field-Affected Reaction Yield Spectroscopy

“…In order to obtain quantitative information about the hyperfine coupling constants in the DMPFPEA and PFPEB radical anions, the MARY spectrum of the PFB radical anion with known A HF values was also recorded. The MARY spectra for this system were observed and interpreted previously, , and the hyperfine coupling constants in PFB radical anion are 27.9 mT (1F), 10.1 mT (2F), and 4.55 mT (2F) Figure shows the experimental MARY spectrum for the solution of PFB in DDC and its numerical modeling (see below).…”

“…Under the experimental conditions used in MARY spectroscopy, the Hamiltonian of RIP (see details in part of the Results and Discussion) conserves the total projection of all spins on the z -axis M z , so the full state space can be divided into nonoverlapping subspaces with different values of M z . Levels belonging to each of these subspaces can be populated simultaneously and the crossings inside the M z blocks, so-called active crossings, contribute to the MARY spectrum. ,− …”

“…For systems with nonequivalent magnetic nuclei, the energy level structure is more complicated and cannot be described by a simple expression. Despite this, the characteristic MARY spectra with specific lines for systems with nonequivalent nuclei have also been reported for the radical anions of fluorinated benzene derivatives: pentafluorobenzene ( PFB ) and 1,2,3-trifluorobenzene. , In both cases the A HF values in the radical anions had been already known from independent experiments, , and the aim of these works was to register the characteristic MARY spectra for these systems and to analyze the correlation between the energy level crossings and the positions of MARY lines in terms of active crossings without detailed modeling. The possibility of determining unknown A HF values using MARY spectroscopy for more complex systems is still questionable.…”

Simple rules for resolved level-crossing spectra in magnetic field effects on reaction yields

“…Several experimental reports of the resolved MARY spectra for systems with nonequivalent nuclei with large HFC constants, in all cases fluorines, have been published. These include radical anions of 1,2,3-trifluorobenzene (Kalneus et al, 2007), pentafluorobenzene (Kalneus et al, 2006b), and recently several fluorosubstituted diphenylacetylenes (Sannikova et al, 2019), again complemented with a radical cation with a narrow ESR spectrum. The spectra featured well-defined lines that were reproduced in simulations and were traced to clusters of level crossings in the spin system of the pair.…”

Comment on mr-2021-6

“…Several experimental reports of the resolved MARY spectra for systems with not equivalent nuclei with large HFC constants, in all cases fluorines, have been published. These include radical anions of 1,2,3-trifluorobenzene (Kalneus et al, 2007), pentafluorobenzene (Kalneus et al, 2006b), and recently several fluorosubstituted diphenylacetylenes (Sannikova et al 2019), again complemented with a radical cation having a narrow https://doi.org/10.5194/mr-2021-6…”