1. A Continuous Supersonic Expansion Discharge Nozzle For Rotationally Cold Ions
Carrie A. Kauffman, Kyle N. Crabtree, Benjamin J. McCall
Department of Chemistry, University of Illinois
June 23rd, 2009

2. Motivation Molecular ions Organic Reaction Intermediates Combustion
Atmospheric Chemistry
Interstellar Chemistry +
Simulation of N2+ of the A 2∏u – X 2∑g+ (4-0)
Due to the low temperatures and pressures that occur in the interstellar medium, ions dominate the chemistry due to their low reaction barriers. In order to probe these species, laboratory spectra are needed. In addition, spectra of these molecular ions would aid in the understanding of organic reaction intermediates, combustion processes, and atmospheric chemistry.

3. Sensitive Cooled Resolved Ion BEam Spectroscopy Supersonic Source
For more on the progress of SCRIBES, stay for the next two talks.

4. Supersonic Expansion Barrel Shock Mach Disk Low Pressure Region
High Pressure Gas
Small Orifice
Adiabatic Process, dq = 0
dU = dq –dw
dU = -PV
Tvib >> Trot > Ttrans , where Trot ~ K

5. Design Considerations
Maximize ion density
Modular
Leak tight
Robust
Compatible with SCRIBES

6. Previous Reported Discharge Designs

7. First Generation - Corona
Advantages
Disadvantages
Continuous
Materials Chosen
No modular components
Compatibility
Engelking, P.C.; Corona Excited Supersonic Expansion. Rev. Sci. Instrum., 1986, 57,

8. Slit Design Advantages Disadvantages Materials Chosen
Integration with SCRIBES
Clustering
Pulsed
Broks, B.; Brok, W.; Remy, J; van der Mullen, J.; Benidar, A.; Biennier, L. & Salama, F.; Modeling the Influence of Anode-Cathode Spacing in a Pulsed Discharge Nozzle. Spectrochim Acta B, 2005, 60,

9. Nozzle Design Advantages Disadvantages Compatibility with SCRIBES
Pulsed
Modular
Materials
McCarthy, M. C., Chen, W.; Travers, M. J. & Thaddeus, P. Microwave Spectra of 11 Polyyne Carbon Chains. Astrophys. J. Suppl., 2000, 129,

10. Design 1-3 Atmosphere of backing pressure
Orifice Size: 250 to 1000 micron with varying geometry
Typical Chamber Pressure 100 mTorr

11. Source Nitrogen Gas Running Voltage: -200 to -500 V
Running Current: 30 mA
Operation Time: 100+ Hours

12. Characterization of the source
Ion Current
Optimization of Cooling Capabilities

13. Summary Design Continuous Supersonic Expansion Nozzle Discharge
Modular
Self-Aligning
Robust

14. Acknowledgements
SCS Machine Shop
McCall Research Group
Ben McCall