Deuterium effect on the pressure coefficient of the tunneling rate in the acridine-fluorene solid-state photoreactive system

We report the pressure effect on the intermolecular deuterium transfer tunn eling rate in the acridine-doped fluorene crystal at 77, 150, and 200 K. Si milar to the hydrogen transfer, the tunneling rate is exponentially enhance d by pressure. The pressure slope for this exponential enhancement, however , is found to be more temperature dependent for deuterium than for hydrogen tunneling. The ratio of the pressure coefficients for H and D stands at 2. 6 at 77 K, gradually decreasing with increasing temperature until it become s essentially unity at room temperature. An intuitive model based on the ma ss dependence of the tunneling distance is presented to rationalize these o bservations.