Fluorescence and dissociative energy transfer in high pressure Ar–HCN mixtures excited by relativistic electrons

Abstract

Studies of the radiation from Ar–HCN and Ar–H2O mixtures, excited by relativistic electrons from a Febetron 706 electron gun, are presented. The energy deposited by the electrons channels rapidly into the Ar* and Ar2* states; then by dissociative collisions with HCN it is transferred partly into the CN(B) state and partly into a reservoir state [most probably the CN(A) state] with near unit efficiency. Fluorescence emission from the electronic states A (2Πi) and B (2Σ+) of the CN radical, as well as the emission from the Ar2* excimer state, were measured for an Ar pressure range of 750–9000 torr [15–180 psi (absolute)], and an HCN pressure range of 0.2–13 torr. The quenching rates of Ar* metastable and the Ar2* excimer states, by collision with HCN molecules, were measured to be 6×10−10 and 1×10−9 cm3 sec−1, respectively. Our results suggest that population inversion can be achieved by collisional dissociation of simple molecules with excited rare gas atoms and excimers. Indeed the peak CN(B) population density was found to be 1.5×1015 cm−3, which corresponds to an optical gain for the B–X transition of 0.4 cm−1 if the ground state is empty. A computer kinetic model is presented that explains the time dependence and intensity of the CN(B) emission. In Ar–H2O mixtures the reaction rate for quenching of Ar2* excimer by H2O molecules is extremely high; however, the yield into the OH(A 2Σ+) is only 3%.