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Investigation of the cw Saturation Technique for Measurement of Electron Spin‐Lattice Relaxation: Application to the Benzene Anion Radical
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22.Perhaps at this point it is appropriate to comment on the differences between the values reported here and those reported by Freed and co‐workers.2j,2k The differences in magnitude are easily explained by the fact that although both groups used 3‐mm‐o.d. sample tubes, were used thin wall tubes and F‘reed and co‐workers used regular glass tubing which has thicker walls. Thus in our case a greater amount of solvent was present in the cavity resulting in a greater depression in the cavity value observed. With respect to our observation of the minimum in we have no explanation. Down to minus 80 °C our results parallel those of Freed and co‐workers at which point our values begin to increase as shown in Fig. 5, whereas Kooser et al.2j,24 report that shows no significant variation with temperature.
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37.Confirmation of this type of interpretation lies in changing spectrometer frequencies to see if the corresponding changes in occur.
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40.This conclusion differs from that reached by Das et al. [Ref. 2(k)] who studied several different systems including benzene. However, it is our opinion that the question of whether the source of the enhanced relaxation in the benzene anion radical is intraor intermolecular is still open. We do not believe that the range of solvents and/or cations over which the benzene anion radical has been studied is sufficient to conclude otherwise. For example, it appears from the work of Jones and co‐workers (Ref. 29) that the benzene anion radical is ion paired over the whole temperature range that it can be studied and in all solvents in which it has been studied. We would change our opinion if studies of the benzene anion radical showed no change for solvents which are more polar than THF, DME, etc., and for which it could be demonstrated that the benzene anion radical was not ion paired.
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