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Electron Paramagnetic Resonance Study of Radical Pairs and Isolated Radicals Trapped in Irradiated Long‐Chain Hydrocarbons at Low Temperatures
Author(s) -
Lin D. P.,
Fan Kuo Wei,
Yeh SiJung,
Chen Grace M.S.
Publication year - 1975
Publication title -
journal of the chinese chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.329
H-Index - 45
eISSN - 2192-6549
pISSN - 0009-4536
DOI - 10.1002/jccs.197500015
Subject(s) - radical , chemistry , radiolysis , electron paramagnetic resonance , photochemistry , squalane , reaction rate constant , arrhenius equation , isothermal process , kinetics , nuclear magnetic resonance , activation energy , organic chemistry , thermodynamics , physics , quantum mechanics
The intrinsic characteristics of radical pairs produced in squalane and in cetane receiving high gamma‐dose are extensively studied with the EPR technique at temperatures from 77° K up to 150° K . The spectra of the paired radicals occur at g=4 with a very low transition probability in contrast to that of isolated radicals which appear at g =2 A well‐resolved hyperfine spectrum corresponding to the species (CH 3 CH 2 .CH 2 CH 3 ) is observed in cetane. The isothermal decay rates of radical pairs in cetane below 100° K are significantly slow; however, the decay kinetics at 150° K is first order with rate constant=1.86 min −1 . A relatively slower decay rate is obtained for isolated radicals suggesting that the decay mechanism of paired radicals is through geminate recombination. The relative inter‐radical distance in radical pairs is known from a decay curve as a function of temperature. The yields of radical pairs are low in both matrices, only few percents of those of isolated radicals. The formation mechanisms of paired radicals with direct radiolytic bond scission process are discussed in connection with the experimental observations.