Rapid frequency scan EPR

Abstract

In rapid frequency scan EPR with triangular scans, sufficient time must be allowed to insure that the magnetization in the x, y plane decays to baseline at the end of the scan, which typically is about 5 T 2 after the spins are excited. To permit relaxation of signals excited toward the extremes of the scan the total scan time required may be much longer than 5 T 2. However, with periodic, saw-tooth excitation, the slow-scan EPR spectrum can be recovered by Fourier deconvolution of data recorded with a total scan period of 5 T 2, even if some spins are excited later in the scan. This scan time is similar to polyphase excitation methods. The peak power required for either polyphase excitation or rapid frequency scans is substantially smaller than for pulsed EPR. The use of an arbitrary waveform generator (AWG) and cross loop resonator facilitated implementation of the rapid frequency scan experiments reported here. The use of constant continuous low B 1, periodic excitation waveform, and constant external magnetic field is similar to polyphase excitation, but could be implemented without the AWG that is required for polyphase excitation.