Pt. 1: Metastable Ion Studies with a /sup 252/Cf Time of Flight Mass Spectrometer. Pt.2: ''Spontaneous'' Desorption of Negative Ions from Organic Solids and Films of Ice at Low Temperature

摘要

Time of flight mass spectrometry associated with a MeV ion source is certainly a good combination to investigate high molecular masses. Since the discovery of the /sup 252/Cf desorption method several P.D.M.S. systems have been built in a number of different laboratories. At our institute a time of flight instrument which was designed for measuring masses of exotic radioactive nuclei has been used for applications in this new field as well as for new instrumental development, another /sup 252/Cf instrument being available for external users. An electrostatic mirror based on the Mamyrin principle has been adapted to improve the mass resolution and to allow for ''in flight'' metastable decay studies. We discuss here briefly the method and present some experimental results. It has been shown that under the effect of a constant voltage applied between a flat metallic surface and a high transmission grid (90%), electrons and negative ions are emitted simultaneously. Time of flight mass measurements can be made by taking electrons as start signals. Mass spectra of organic samples have been compared with those obtained by PDMS. The method - named by us ''Spontaneous'' Desorption Mass Spectrometry - has also been used to study the emission from a cooled ice target and its dependence with temperature (from 77 to 200K). Experimental investigations on the mechanisms are presented. (ERA citation 12:027930)