A CIDEP study of p -benzosemiquinone

• Published in: The Journal of chemical physics 1975-09, Vol.63 (6), p.2398-2405
• Main Authors: Pedersen, J. Boiden, Hansen, C. E. M., Parbo, H., Muus, L. T.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.431668

Chemically induced dynamic electron polarization (CIDEP) from photolytically generated p-benzosemiquinone radicals is studied by time resolved steady state experiments. The experimental time resolved intensity curves are fitted to curved derived from theory. Two different polarization contributions are observed with ethylene glycol as solvent. A hyperfine independent initial polarization P∞(I) =−0.107 is due to a triplet mechanism (TM) and a hyperfine dependent polarization (−0.032?P*⩽0.032) is caused by a radical pair mechanism (RPM) due to the radical termination reaction. P∞(I) =−0.034 when isopropanol is used as solvent. The solvent dependence of P∞(I) is consistent with the microscopic theory and the observed values of P∞(I) are indicative of a triplet lifetime in the range 0.1–10 nsec and a zero field parameter ‖D‖≳700 G. The magnitude and hyperfine dependence of P* is in accord with the microscopic theory for an exponentially decaying exchange interaction J (r) with the maximum value J0≳109 rad/sec. The separation at which J (r) is decreased by a factor 105 equals the distance of closest approach (?6.5 Å).