The EPR spectrum of the general Ċ–CX3 quantum rotor Original Research Article

The quantum mechanical Liouville equation for the general Ċ–CX3 rotor is employed to obtain low temperature electron paramagnetic resonance (EPR) spectra exhibiting E-line splittings arising from the spin-rotational coupling in the hyperfine interaction. Analytic expression for the low temperature EPR spectrum for the general C3-symmetry rotor is presented. Analytic spectra for I=1/2, 1 and 3/2 nuclei-containing rotors are discussed in detail. Intensities and positions of first order transition sidebands are given for the general system and explicitly discussed for I=1/2 and 1 systems, with high accuracy determination of tunnelling frequencies and potential twist angles from low temperature experimental data as possible applications. Anomalous A/E mixing effects on the EPR spectrum in the transition region between tunnelling and stopped rotor conditions are demonstrated for I=1/2 and 1 systems and a particular choice of twist angle.