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GAS COMPOSITION CONTROL FOR A PULSED NOZZLE FT MICROWAVE SPECTROMETER AND APPLICATIONS

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/18152

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Title: GAS COMPOSITION CONTROL FOR A PULSED NOZZLE FT MICROWAVE SPECTROMETER AND APPLICATIONS
Creators: Emilsson, T.; Germann, T. C.; Gutowsky, H. S.
Issue Date: 1990
Abstract: Pulsed supersonic jets of inert carrer gases needed with more reactive species are used to generate small clusters for a varioty of experiments. In our case it is the sample source for a Balle/Flygare Fourier tranaform microwave spectrometer used to observe rotational transitions of the clusters and determine their structure. In such experiments, acourate control of the small concentrations of reactive species is both important and can be difficult. A system has been built which permits rapid (5 nec) and reproducible control of the composition and pressure of gas mixtures supplied to the nozzle. Typical samples consist of an arbitrary mixture of two inert gases seeded with one or two other substance at concentrations between several ppm to several percent. The concentration of each ingredient can be controlled to about 1 of its value. The system is comprised of four mass flow controllers (MKS, Instruments, Model 1259) and a micro-processor based programmer (MKS, Model 147), as well as a handful of small bore valves and miscellaneous plumbing. The gas control system is being used to explore kinetic features of the supersonic expansion in the specetrometer. For example, one may inquire whether the first step in the formation of an $Ar_{2}-HCN$ trimer is the formation of $Ar_{2}$ or of Ar-HCN, or both. The intensity observed for the $1_{11}+2_{02}$ transition of the trimer at 4312,38 MHz, using first run neon (70\% Ne, 30\% He) as the carrier gas, shows it to be first order in [Ar] and in [HCN]. This suggests that Ar2-HCN is formed primarily from Ar-HCN and Ar. The details of this and related experiments will be described.
URI: http://hdl.handle.net/1811/18152
Other Identifiers: 1990-RB-10
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