Skew projection of echo-detected EPR spectra for increased sensitivity and resolution

Abstract

The measurement of EPR spectra during pulsed EPR experiments is commonly accomplished by recording the integral of the electron spin echo as the applied magnetic field is stepped through the spectrum. This approach to echo-detected EPR spectral measurement (ED-EPR) limits sensitivity and spectral resolution and can cause gross distortions in the resulting spectra because some of the information present in the electron spin echo is discarded in such measurements. However, Fourier Transformation of echo shapes measured at a series of magnetic field values followed by skew projection onto either a magnetic field or resonance frequency axis can increase both spectral resolution and sensitivity without the need to trade one against the other. Examples of skew-projected spectra with single crystals, glasses and powders show resolution improvements as large as a factor of seven with sensitivity increases of as much as a factor of five.

The tetrahydrobiopterin radical interacting with high- and low-spin heme in neuronal nitric oxide synthase – A new indicator of the extent of NOS coupling

“…The slow-relaxing spectrum is asymmetric and considerably broader than that of the fast-relaxing signal. Its wings are consistent with the CW-EPR spectrum of nNOS FQ (+BH 4 , − l -arg) considering that the ED-EPR spectra have some additional broadening from the measurement conditions [25, 47]. …”

Spin–spin interactions and spin delocalisation in a doped organic semiconductor probed by EPR spectroscopy

“…Fourier transform of the echo or FID signals followed by projection onto a magnetic field axis and summation results in pulse EPR spectra with increased sensitivity, and in some cases increased resolution, compared to standard pulse measurements performed by echo integration. 43 For F 4 TCNQ-doped P3HT films at a doping ratio of −2 , both the echo as well as the FID after a selective pulse (t π/2 =200 ns) give the same spectrum as obtained by echo integration. At a doping ratio of 2.5 • 10 −2 , the echo intensity has significantly decreased compared to the FID intensity on account of the faster spin-spin relaxation, and an additional contribution to the FID transients becomes evident.…”

Control of excitation selectivity in pulse EPR on spin-correlated radical pairs with shaped pulses

“…A selected echo transient is shown in the top left panel, and the corresponding Fourier transform is compared to the calculated pulse excitation profile in the top right panel. The echo-detected field sweep spectrum was constructed in the frequency domain as the sum of the individual echo Fourier transforms at different magnetic fields, following an approach first proposed by Bowman et al 63 for obtaining echo-detected spectra with increased spectral resolution and sensitivity compared to echo integration. The in-phase and out-of-phase contributions of the resulting echo-detected spectrum are compared to the EPR spectrum recorded using transient EPR on the top right.…”