Simultaneous optical detection of chlorine NQR of p-dichlorobenzene in its non-radiative S o and phosphorescent T 1 state in a mixed single crystal

Abstract

By a combined optical and microwave pumping cycle electron spin alignment is transferred to the diluted chlorine nuclear spins. Because of the conservation of nuclear spin alignment during the electronic excitation and phosphorescence decay, NQR transitions within the excited triplet and electronic ground state of p-dichloro-benzene ( p-DCB) can be detected optically in a dilute mixed single crystal. A detailied analysis of NQR transition frequencies and intensities in the T 1 state has been performed. For the first time the change of the molecular field gradient under electronic excitation could be observed at the chlorine site. The NQR frequency change Δν q(S o, T 1) was found to be matrix dependent and varied from 2.52 MHz ( p-dibromobenzene) to 3.75 MHz (xylene).