Generation of “bastard” molecular ions from van der Waals clusters: Ar_n(C₂Cl₄)_m⁺ ions, suspected interlopers in collection of solar neutrinos

Abstract

Gaseous molecular ions containing argon and perchlorethylene, Ar_n(C₂Cl₄)_m ⁺ in which n ≥ 1-29 and m ≥ 1-4, are produced by electron bombardment of van der Waals clusters formed by expanding an Ar/C₂Cl₄ mixture through a supersonic nozzle. Previous attempts to observe such ions in a high-pressure mass spectrometer were not successful, as with many other (“bastard”) ions that similarly lack a stable chemically bound neutral parent molecule. This is probably due to dissociation induced by the large exoergicity from charge transfer between species that differ greatly in ionization potential. Use of van der Waals clusters as parent species avoids entirely the exoergicity problem and thus offers a general method to generate bastard ions. The Ar(C₂Cl₄)_m ⁺ ions have been suspected of interfering with collection of ³⁷Ar⁺ ions produced by the ³⁷Cl(v,e^-)³⁷Ar⁺ reaction in the solar neutrino observatory. Although, as shown by our results, these ions are stable, they are unlikely to inhibit collection on the long time scale of the solar neutrino experiment.

• molecular beam
• supersonic expansion
• mass spectroscopy