New experimental and theoretical techniques in gas electron diffraction for determination of molecular structures of low-volatile and unstable compounds

This project is devoted to the development of gas electron diffraction – one of the main direct experimental methods for determination of molecular structures in the gas phase. The main goal of the development is to enable investigations of low-volatile and unstable substances. For this, a new experimental approach is introduced, termed low-pressure gas electron diffraction (LPGED). Current instrumental limitations of this approach will be eliminated by constructing a new evaporator with improved heating and a possibility to study air-sensitive compounds. In tandem with online mass-spectrometric control this will provide a capability to measure accurate diffraction patterns of high quality. From the other side new techniques for data processing, structural refinement and analysis are developed, which are especially important for large and flexible molecules. For demonstrating the capabilities of these new experimental and theoretical methods there will be done a series of investigations for some known as well as new compounds from different classes. These include complexes with gallium, biradicaloids with phosphor and arsenic, boron cage compounds, including one nickel bis(dicarbollide) and gold compounds. The substances have been chosen so that their gas-phase molecular structures can hardly be studied by classical electron diffraction but could probably be obtained due to the new methods from this project. The refined molecular structures will be of great importance for understanding the chemistry of the compounds and for further research in these fields.

Updated GED unit at Bielefeld University
Figure 1. Photograph of the gas electron diffraction instrument at Bielefeld University combined with the quadrupole mass-spectrometer. A — control panel, B — ampule with substance, C — evaporator (in the middle position on the photograph), D — diffraction chamber, E — cold trap reservoir for liquid nitrogen, F — mechanical valve, G — position of the ionisation chamber, H — ion gauge, I — control device for the turbo pump and the ion gauge, J — turbo molecular pump, K — chamber with the quadrupole mass-spectrometer probe, L — amplifier head, M — frame for the mass-spectrometer unit, N — electron gun.

From the experimental point of view the most important publications made within this project are:

Y. V. Vishnevskiy, S. Blomeyer, C. G. Reuter, O. A. Pimenov, & S. A. Shlykov, Combined gas electron diffraction and mass spectrometric experimental setup at Bielefeld University. Rev. Sci. Instrum., 91 (2020) 073103.

Y. V. Vishnevskiy, S. Blomeyer, & C. G. Reuter, Low pressure gas electron diffraction: An experimental setup and case studies. Rev. Sci. Instrum., 91 (2020) 074104.

The procedures for data processing are developed within the long-standing projects UNEX and Mir.