Use of Oxygen Gas in the Low-Temperature Time-Resolved EPR Experiments

A large transient microwave signal seen in low-temperature time-resolved electron paramagnetic resonance (TREPR) experiments is attributed to the presence of nitrogen as a flushing gas, when pulses of a 266- or 248-nm laser light is used for photolysis. We report here that, using oxygen as the flushing gas, this transient can be largely removed. Based on the studies using 355 nm laser light and also nitrous oxide as the flushing gas, photoelectron emission from the inner walls of the microwave cavity is proposed to be the origin of this transient, and the electron attachment to oxygen gas is the mechanism of its removal. Using oxygen as the flushing gas, recording of TREPR spectra at low temperatures as well as very close to the laser pulse of 266 or 248 nm is possible.