A Rydberg-atom ionization source for negative ion mass spectrometry

Abstract

An ion source for negative ion mass spectrometry has been developed. The ionization method is based on the collisional electron transfer from a high-Rydberg atom (A **) to a target molecule which possesses a positive electron affinity. In this ionization process, negative ions are directly produced via resonance capture of the “quasi-free” Rydberg electrons: A ** + M → A + + M −. In contrast to negative chemical ionization, the Rydberg-atom ionization proceeds at a low pressure of ≈ 10 −3 Pa. The method was applied to several molecular systems, such as 1-decanethiol, 3-nitrobenzyl alcohol and o-nitrophenyl octyl ether.