Photoionization of magnesium and copper phthalocyanine in oxygen and hydrogen

The photoionization energies of magnesium phthalocyanine (MgPC) and copper phthalocyanine (CuPC) single crystals are determined in different ambient atmospheres by an electrostatic method. The sample crystal is suspended by a quartz fibre in an electric field between two capacitor plates, and the onset of ionization with photon energy is determined through the potential required to restore zero deflection. Results of threshold energy φ for MgPC and CuPC crystals in a clean ultrahigh vacuum of 10−9 Torr and the changes in φ produced by adsorption in 10−2 Torr oxygen and hydrogen atmosphere are presented. The φ values in vacuum obtained here are comparatively lower than those reported by previous workers. The striking features observed in the adsorption of oxygen and hydrogen are that the classic electron donor, hydrogen, raises the threshold of ionization whereas oxygen does not effect any change in the threshold from its value in vacuum. Experiments have also established that MgPC and CuPC do not exhibit a double quantum photoemission.