Electrospray and charge reduction in the gas phase

A key goal of our project is to extend quantum interferometric experiments to matter of biological relevance like large peptides, proteins, DNA strands and eventually viroids.

The development of electrospray ionisation (ESI) and matrix assisted laser desorption and ionisation (MALDI), have revolutionized biopolymer mass spectrometry because they are minimally invasive. Starting with charged biomolecules we can mass-select, guide and focus them with DC and RF fields.

For experiments in quantum optics the particles should be neutral, to avoid decoherence with electric stray fields. Here we propose to achieve their neutralisation in a two steps process. First, the molecules can be charge-reduced, in polar air, for instance created in plasma discharge [4].

Singly charged molecules can still be mass selected in a quadrupole mass filter as well as cooled and slowed in a cryogenically cold 2D hexapole guide, where cold neutral noble gas atoms, at a temperature of 30-70K, thermalize with the molecular beam by collisions. 

A key challeng is to devise a soft neutralization step in a controlled photo-reaction.  Our first efforts have showed that site-specific cleavage can be achieved in a high vacuum environment for small model systems [5].

References

[1] Eibenberger S, Gerlich S, Arndt M, Tüxen J and Mayor M, New J. Phys. 13, 43033 (2011)

[2] Gring M et al, Phys. Rev. A, 81, 031604(R) (2010)

[3] Eibenberger S, Cheng X, Cotter JP and Arndt M, Phys. Rev. Lett., 112 250402 (2014)

[4] Scalf M, Westphall MS and Smith LM, Analytical chemistry,72(1), 52-60, (2000)

[5] Sezer U , Geyer P, Kriegleder M, Debiossac M, Shayeghi A, Arndt M, Felix L and Mayor M, Beilstein J. Nanotechnol. 2017, 8, 325–333 (2017)

Partners on the experiment

MSc Jonas Schätti, Dr. Valentin Köhler, Prof. Marcel Mayor
University of Basel,
Departement of Chemistry