Inverse Deuterium Isotope Effect in the Intersystem Crossing of Diphenylcarbene

They are important chemical intermediates whose spin state dependent chemistry is implicated in a large number of organic reactions [l-4]. An important feature relevant to an understanding of many of their physical and chemical properties is the small energy gap separating the lowest singlet and triplet states. In fact for a number of carbenes these two states are in equilibrium at room temperature [5]. The ground state of these molecules can be either singlet or triplet depending on substituents and possibly geometry [6]. For the molecules we have studied, diphenylcarbene (DPC) and dibenzocycloheptadienylidene @CHD), DPC