Frequencyhyphen;Swept Electronndash;Electron Double Resonance: DPPH in Liquid and Frozen Solution

摘要

Instrumentation for frequencyhyphen;swept electronndash;electron double resonance (ELDOR) at X band is described. Reliable control of the sweeping (pump) microwave frequency to 1 part in 106(10 kHz) has been achieved. The technique has been applied to liquid and frozen solutions of DPPH in toluene. The isotropic nitrogen coupling constants areAagr;thinsp;equals;thinsp;7.933thinsp;plusmn;thinsp;0.007andAbgr;thinsp;equals;thinsp;9.739thinsp;plusmn;thinsp;0.014Gincluding secondhyphen;order corrections. The ratioAagr;thinsp;sol;thinsp;Abgr;thinsp;equals;thinsp;0.815. In the solid phase the largest hyperfine coupling to theagr;hyphen;nitrogenverbar;thinsp;Athinsp;plus;thinsp;2Bthinsp;verbar;agr;and the largest hyperfine coupling to thebgr;hyphen;nitrogenverbar;thinsp;Athinsp;plus;thinsp;2Bthinsp;verbar;bgr;are each 20.1 G. The literature on this molecule is reviewed and the present experiments discussed in this context. Much of the paper is devoted to the physical basis of ELDOR spectroscopy. An analysis of ELDOR line shapes is given in an appendix.