Negative-Ion Mass Spectrometry by Use of Collisional Ionization of High-Rydberg Atoms

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This research project was undertaken to establish a negative-ion mass spectrometry by use of collisional ionization of high-Rydberg agtoms. The basic principle of this ionization method is to use the outermost electron of Rg^<**> which is collisionally transferred to a target molecule with an efficiency 10^4 times as high as that for electron-impact ionization. In addition, the excess energy associated with the electron attachment can be minimized because of a small kinetic energy of the electron (10 - 20 meV). The following studies showed that this method of ionization is applicable as an ion source for the mass analysis of weakly-bound polymer molecules and molecular having postive vertical electron affinities.1. Studies on electron transfer from high-Rydberg rare gas atoms to van der Waals clustgersvan der Weals clusters of H_2O, NH_3, CH_3CN, (CH_3)_2CO, SF_6, CO_2, N_2O etc. wre ionized in collision with high -Ryodgerg Krypton atoms produced by electron impact. The mass spectroscopiec studies of negative ions thus produced revealed that the collisional electgron transfer provides a unique method for efficient and gentle production of negative cluster ions.2. Development of a negative-ion mass spectrometer equipped with a high-Ryodberg atom sourceAn ion source based on the ionization method mentioned in section 1 was made and mounted to a JEOL magnetic sector-type mass spectrometer of the central Technical Research Laboratory of NIPPON OIL Co., Ltd. Several samples, such as glutamic acid, perylene, benztriazole etc., wre examined and the parent negative ions of these species were obtained.