Two-Pulse Electron Spin Echo of Biradicals: Dependence on Pulse Turning Angles

Double spin labeling is often used to study the conformations of biomolecules using pulsed dipolar EPR spectroscopy (PDS). For spin labels based on triarylmethyl (TAM) radicals, there is a data processing problem due to the strong dipole–dipole coupling of the two spins due to the narrow EPR line. As recently shown, these problems can be overcome in a simple PDS approach based on two-pulse electron spin echo spectroscopy (2p ESE). Although the theory underlying this approach was developed by Salikhov and Zhidomirov many years ago, all of its predictions, however, have yet to be tested. Here we obtain additional arguments in favor of the applicability of this theory by investigating the dependence of the echo signal on the pulse turning angles. In addition, we show how the results obtained can be useful for data processing in PDS methods.