The accelerator-based mass spectrometry of methane

Abstract

Accelerator-based Mass Spectrometric (AMS) methods have not been generally applied to the analysis of molecular species because of difficulties with ion sources and the fact that tandem accelerators are not generally applicable. A method has been developed to measure the abundance of fully deuterated methanes, 13 CD 4 and 12 CD 4 , in normal methane by using AMS. A low-energy electron bombardment ion source has been coupled to a single-ended electrostatic accelerator to produce positively charged molecular ions. The ions are accelerated, mass selected, and then dissociated into fragments that are detected by nuclear particle detection methods. In this way information about the composition of the original molecule, as well as the mass, is obtained. Measurements on natural neon, 12 CH 4 , 12 CD 4 , and 13 CD 4 have been made, and new approaches to the stabilization of accelerator voltage and isotopic abundance calibration are presented. Possible applications for analysis of other molecules not easily measured with conventional AMS are considered.