Emission spectra of glows produced by ionic liquid ion sources

Abstract

Electrospray devices, such as ionic liquid ion sources, often exhibit glows during operation in high vacuum facilities. The lack of electron excitation mechanisms during electrospray operation prompts the question: “What causes glow in an electrospray device?” Our optical emission spectroscopy results show that electrospray glow exhibits a broad spectral response between 350 and 800 nm with emission lines corresponding to atomic metal constituents of impinged surfaces, neutral and ionized atomic constituents of the ionic liquid propellant, and molecular line shapes that may also be dissociation products of the ionic liquid. We have previously defined secondary species emission to describe the many complex interfacial phenomena that occur when electrosprayed species impact surfaces downstream of the emitter. Our analysis of the optical emission spectra shows that these glows are only possible in the presence of secondary species emission. Therefore, the answer to the proposed question: high-velocity impacts that generate secondary species are the root cause of glow for electrosprays in high vacuum facilities.