Positive hole hopping in glassy alkanes at 77 K: observation by the OD ESR technique

• Published in: Chemical physics letters Vol. 171; no. 5; pp. 413 - 422
• Main Authors: Tadjikov, B.M., Lukzen, N.N., Anisimov, O.A., Molin, Yu.N.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 17.08.1990; Elsevier Science
• Subjects: Chemical reactivity; Chemistry; Exact sciences and technology; Organic chemistry; Reactivity and mechanisms; Matrix isolation; Theoretical study; EPR spectrum; Hydrocarbon; Charge transfer; Glassy state
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/0009-2614(90)85239-9

The optically detected ESR spectra of radical cations of 3-methylpentane, 3,3-dimethylpentane, 2-methylpentane, 2,3-dimethylbutane and other branched alkanes in their glassy matrices at 77 K display an anomalous ratio of hyperfine component intensities observed in an increase of the intensity of weak components towards the binomial distribution. A theory of uncorrelated frequency migration accounts for this phenomenon, assuming motion of relaxed solvent holes via charge transfer between the solvent molecules. Comparison between the experimentally observed and theoretically calculated spectra gives quantitative parameters for this process. The results obtained show that the hole-residence time depends on the matrix and equals 0.1–0.2 μs for 3,3-dimethylpentane and 0.5–0.8 μs for 3-methylpentane at 77 K. Thus, the geminate solvent hole recombination in a glassy alkane matrix is preceded by a hopping motion among matrix molecules.