Enhanced Resolution in EPR Spectroscopy Using <i>para</i> ‐Hydrogen Matrices

Abstract

Abstract We developed a matrix isolation experiment utilizing a closed‐cycle helium cryostat, which operates at 2.5 K and enables electron paramagnetic resonance (EPR) measurements in solid para ‐hydrogen ( p ‐H 2 ) matrices. The EPR spectra of the persistent 2,2,6,6‐tetramethylpiperidinyloxyl ( TEMPO ) radical and an in situ generated P ‐centered mono‐radical were recorded at 2.5 K in p ‐H 2 . The spectrum of TEMPO in p ‐H 2 shows a narrower linewidth compared to argon, and its matrix‐isolated spectrum and simulation are reported. The P ‐centered mono‐radical was generated in p ‐H 2 via in situ photolysis of the corresponding phosphorus iodide, which affords roughly a three‐fold increase in spectral resolution compared to argon, as well as higher sensitivity due to the non‐existing cage effect in soft p ‐H 2 .