Pulsed ion deflection to overcome detector saturation in cryogenic ice sampling

Abstract

In 2014, we introduced a new experimental approach to study the UV photo-processing of cryogenic ices of astrophysical interest using laser ablation in combination with ionization and time-of-flight mass spectrometry (ToF-MS). The setup, MATRI${}^2$CES (Mass Analytical Tool to Research Interstellar ICES), allowed us to detect newly formed species at low abundances. However, we found that with increasing molecular complexity, the detection of larger photoproducts was hindered by the dynamic range of the detector. Here, we introduce a method to overcome this issue that we expect to be useful for similar applications in other research fields. The concept is based on a precisely controlled high-energy pulser that regulates the voltage across the deflection plates of the ToF-MS to deflect the most abundant species and prevent them from reaching the detector. In this way, the detector sensitivity can be increased from an operating voltage of 2500~V up to 3000~V. The applicability is first illustrated using an argon matrix, in which ${}^{40}$Ar${}^{+}$ ions are deflected to increase the detection sensitivity for ${}^{40}$Ar${}^{2+}$ at $m/z=20$ and ${}^{40}$Ar${}_2^{+}$ at $m/z=80$ by a factor of 30. Similarly, we show that substantially larger complex organic molecules can be measured in UV-irradiated methanol ice.

arXiv comment24 pages, 8 figures

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• In situ characterization of volatile and refractory hydrocarbons produced by UV photolysis of interstellar C${}_2$H${}_2$ ice