FT-EPR with a Nonresonant Probe: Use of a Truncated Coaxial Line

Abstract A truncated transmission line probe (TLP) has been utilized to excite and detect time domain responses after pulsed excitation in electron paramagnetic resonance (EPR) spectroscopic experiments in the frequency range 200–400 MHz. The TLP device is a modified short-circuited coaxial line, which allows the irradiation of the sample by the traveling wave B 1 fields in the frequency range of kilohertz to 30 GHz. In EPR studies at 300 MHz carrier frequency, with 10 W incident power, a 45° pulse is 45 ns in duration. This corresponds to a 0.9-G B 1 field. Using the TLP, time-domain responses from the solid N -methyl pyridinium tetra -cyanoquinodimethane (TCNQ) were collected at 200, 250, 300, and 350 MHz, with the range limited by the amplifiers. In addition two tubes containing TCNQ placed side-by-side vertically along the axis of the probe were used to collect time domain responses in the presence of magnetic field gradients to test the feasibility of two-dimensional imaging using a TLP. The magnetic field gradient was steered in the xz plane and 36 projections were collected at 5° intervals. Using filtered back-projection image reconstruction, the two-dimensional spatial image in the xz plane was obtained at good resolution.