Plasma Chemistry

Both ions and neutral radicals are potential stepping-stones between the hydrogen-dominated chemistry of diffuse clouds and the complex organic chemistry observed in dense star-forming regions. We use plasma discharge to prepare these ions and radicals so that we can do laboratory spectroscopy on them.

In our laboratory, we have two plasma sources: a hollow cathode, and a supersonic expansion source. Our liquid-nitroge-cooled hollow cathode, based on the design of T. Amano [1], is an efficient discharge source to produce positive ions, especially protonated species. The copper cathode is housed in a PVC cell where appropriate precursor gases can flow continuously through. A high voltage source is then coupled to an anode, positioned halfway along the length of the cathode, and the resultant discharge produces a plasma that fills the length of the cathode tube. We intend to study important protonated ions in the ISM ion chemistry such as the floppy H₅+.

The supersonic expansion source, based on the design of M. C. McCarthy [2], arcs through the starting of a supersonic molecular beam. This source is versatile in producing neutral molecules, radicals, ions and molecular complexes.

[1] T. Amano, J. Opt. Soc. Am. B, 2, 790 (1985).
[2] M. C. McCarthy et al., Astrophys. J. Suppl. 129, 611 (2000).