Electron Ionization of Size-Selected Positively and Negatively Charged Helium Droplets

Abstract

A beam of size-selected charged helium droplets was crossed with an electron beam, and the ion efficiency curves for the product droplets in all different charge states were recorded. We estimate that the selected helium droplets on their passage through the electron beam are hit by several hundred electrons which can interact with the individual He atoms of the droplets. Reaction channels corresponding to the removal or capture of up to eight electrons were identified, and in all cases, inelastic scattering and the formation of metastable helium played a significant role.

Efficient Formation of Size-Selected Clusters upon Pickup of Dopants into Multiply Charged Helium Droplets

“…In the present paper, we present a novel approach to obtain intense beams of mono-dispersed singly charged cluster ions of almost any kind via pickup of gas phase dopants into multiply charged helium droplets. Droplets containing up to several billion helium atoms [ 16 , 17 , 18 ] can be formed via expansion of precooled pressurized helium through small nozzles into an ultra-high vacuum [ 19 , 20 ]. Evaporative cooling leads to an isothermal temperature of these droplets of about 0.4 K [ 21 ] and collisions with dopants lead to pickup and aggregation of these species to clusters [ 22 , 23 ] and nanoparticles [ 24 ] inside (heliophilic dopants) or on dimples at the surface of the helium droplets (heliophobic dopants) [ 25 , 26 ].…”

“Atoms” Special Issue (Electron Scattering in Gases—From Cross Sections to Plasma Modeling)

“…In this volume, we present a "cross-section" of different approaches, applications and processes, from industrial plasmas [3,4] to molecules of biological interest [5][6][7]; from experiments at ultra-low temperatures [8,9] to processes relevant for thermonuclear synthesis [10]. Thanks to a global response to the invitation, this volume hosts in an equilibrated manner the experimental aspects [6,8,9], ab-initio theories [7,[10][11][12] and semi-empirical approaches [13][14][15][16], both for electron and positron scattering [11,[15][16][17].…”

“…Liquid helium droplets are able to capture atoms and molecules, clusters may form inside them and the spectroscopy of cold molecules inside a neutral matrix is possible. Laimer et al [9] used a tandem mass spectrometer to study the collision of electrically charged He droplets with electrons with variable energy (0-120 eV). By changing the energy of the first electron beam, from 40 eV to 30 eV, positively or negatively charged droplets, with up to 100 million He atoms, can be produced.…”