Grant: Research Tools and Instruments - Category 1 (<$150,000)

Helium nanodroplet isolation spectroscopy has become a versatile tool for the stabilization and study of unstable species. Even more remarkable is the use of helium droplets as nanoreactors. For this purpose, helium nanodroplets, which consist of several thousand up to several million helium atoms, can be doped with reactive species. At the very low temperature of 400 mK, a chemical reaction will occur if it is barrier-less or through a tunnelling mechanism if a low barrier exists or it can be photo-induced. We have developed a promising research program to study chemical reactions of atmospheric and astrophysical relevance using the method of helium nanodroplet spectroscopy. Of particular interest to us are reactions involving the OH radical, which plays a particularly important role as Earth's atmospheric ""vacuum cleaner"". Methods to produce reactive species, such as pyrolysis or electric discharge, are often ""dirty"" and introduce undesired by-products into the helium nanodroplets. This poses significant problems since the by-products will immediately associate with the reactant at the low droplet temperature. Therefore, a clean source for reactive species is needed. Clearly the most suitable and versatile of such sources is photolysis. An ultra-violet laser can be used, for example, to dissociate hydrogen peroxide to form two OH radicals. Since our spectrometer employs a continuous helium droplet source, a laser with high repetition pulse rate is needed to provide a quasi-continuous source of radicals. An 193 nm excimer laser with a 1 kHz repetition rate is ideal for this task and funding is requested for the purchase of such as system.