EPR Study of Tetracene Positive Ion

Abstract

The EPR response of tetracene positive ion formed by dissolving tetracene in concentrated sulfuric acid has been investigated in detail. The splittings of the hyperfine lines have been carefully measured and the spectrum analyzed. Relaxation processes (T₁ and T₂) have been investigated over a range of experimental conditions. At low temperatures anisotropic hyperfine interactions determine linewidths and result in asymmetric spectra. This asymmetric interaction differs for the various classes of protons and depends on the form of the hyperfine tensor for each class. A second broad resonance of integrated intensity equal to that of the tetracene positive ion has been detected. In one experiment deuterated sulfuric acid was used, and it was found that the deuterium exchanged with the tetracene protons. Considerable attention has been paid to experimental techniques useful in investigating narrow line spectra. Both 100‐kc field modulation, where modulation sidebands were encountered, and superheterodyne detection have been employed. Linewidths as narrow as 35 mG have been obtained.