Knowledge Bank

Optically detected magnetic resonance experiments under pressure in excess of 40 kbar have been performed in several triplet state aromatic molecules. The sample is contained in a small hole in a metal gasket in a diamond anvil high pressure cell. A judiciously designed hairpin effectively couples microwave magnetic field to the sample. Data will be reported for p-dichlorobenzene (DCB) in p-xylene, s-tetrachlorobenzene (TCB) in durene and quinoxalene (Q) in durene. The zero-field parameter D decreases linearly with increasing pressure, whereas E has more subtle changes. These results are interpreted in terms of the mesomeric effect in chlorobenzenes and the inductive effect in azeromatics. The quadrupolar field gradient of the $C135$ isotope has been measured as a function of pressure. Its decreasing tend corroborates the above picture.