Molecular and applied modulation effects in electron electron double resonance. V. Passage effects in high resolution frequency and field swept ELDOR

The observation of electron electron double resonance (ELDOR) linewidths for nitroxide radicals which are significantly less than the hyperfine envelope widths is reported. For a 1.5×10−3M solution of 2,2,6,6‐tetramethyl‐4‐piperidinol‐1‐oxyl (TANOL) in sec‐butylbenzene (SBB) between the temperatures of −40 °C and −70 °C, the ELDOR linewidths correspond to single spin packet widths determined by the effective electron spin–spin relaxation rates. An analysis of the precise dependence of frequency swept absorption and dispersion ELDOR signals upon microwave radiation field intensities and upon the details of the applied Zeeman modulation and accompanying phase‐sensitive detection is also presented. Quantitative prediction of molecular and applied modulation effects is accomplished employing a modified density matrix treatment. Best fit parameters for TANOL in SBB at −63 °C include we(0) = 1.75×105 Hz, Te1e(0) = 1.3×10−6 sec, Te2e(0) = 2.7×10−7 sec, wn(14N) = 2.6×105 Hz, wn(all 1H) = 0 Hz, τ2 = 2×10−10 sec, ?...