Tandem mass spectrometry of helium nano droplets

Abstract

In this thesis, helium nano droplets in highly charge states are analyzed. The helium nano droplets are formed in a free jet expansion source. Previous measurements showed a phenomenon, in which a narrow peak at relative small droplet sizes occurred in the size distribution of helium nano droplets, when high ionization power was applied. To test this, a tandem mass spectrometer of two identical 90 degree spherical capacitors with tunable voltage is realized. An ion source is mounted in front of each electrostatic sector. Behind the two sectors, the droplets are detected by a Channeltron Electron Multiplier (CEM). The first attempted explanation of the observed phenomenon as a fragmentation of the helium droplets via Coulomb explosion, is disproven. The insights gained by measurements using this setup suggest that the occurrence of the peaks in the size distribution can be explained by multiply charged helium droplets rather than their fragmentation. Furthermore, the minimum size of a helium droplet in a certain charge state is determined.Lukas TiefenthalerUniversität Innsbruck, Masterarbeit, 2018(VLID)280243