The Performance Of A Continuous Supersonic Expansion Discharge Source Carrie A. Kauffman, Kyle N. Crabtree, Benjamin J. McCall Department of Chemistry, University of Illinois June 24th, 2010

Outline 1. Motivation 2. Source Design 4. Conclusion 3. Results

Motivation

Motivation Interstellar medium: Diffuse Molecular Clouds Temp ~ 60 K Density ~ 101–103 cm-3 Dense Molecular Clouds Temp ~ 20 K Density ~ 104–106 cm-3

Sensitive Cooled Resolved Ion BEam Spectroscopy For more on SCRIBES, please stay for RE06.

Production of Cold Molecular Ions Trot ~ 300+ K Trot ~ 110-180 K

Production of Cold Molecular Ions Trot ~ 110+ K -No spectral intensity dilution, reduced spectral congestion -> easy spectral assignment -Astrophyiscally relevant temperatures-> molecular fingerprint for astronomers

Continuous Supersonic Expansion Discharge Source Small Orifice Trot ≈ 5-30 K High Pressure Gas Low Pressure

Continuous Supersonic Expansion Discharge Source Leybold 3-Stage Pumping System Pumping speed ~ 3600 L/s

Basic Design Gas Input High Temp Silicone O-rings Cathode Macor Cap Anode Macor Spacer

H3+ Rotational Constant: 43.56 cm-3 R(1,0) R(1,1)u R(2,2)l McCall, B.J. Ph.D. Thesis, University of Chicago, 2001.

Experimental Set-up

Source Conditions 2-3 bar of backing pressure Orifice Size: flared like a trumpet 0.5 to 4.1 mm in diameter Typical Chamber Pressure 200-300 mTorr Negative voltage applied to cathode and anode held at ground Current: 10-130 mA

Sample Spectra

Results Low Current Regime ↑ column density with increasing discharge current. ↑ in rotational temperature with increasing discharge current. Operated for over 150 hours without source failure.

Results High Current Regime ↑ column density No change in rotational temperature 50 hours of operation

Comparison This Work Xu et al.1 Tom et al.2 Davis et al.3 Type of Source Continuous nozzle Continuous slit-jet corona Pulse Nozzle Pulsed Slit Rotational Temperature (K) 50-110 77 60-100 Not Reported Ion Density (cm-3) 8 × 1010 to 2 × 1012 1 x 1011 5x1010 1. Xu et al. Chem. Phys. Lett. 1995, 242 126-131. 2. Tom et al. J. Chem. Phys. 2010, 132, 081103. 3. Davis et al. Chem. Phys. Lett. 2001, 344, 23-30.

Summary Rotational temperatures in the range of 50-110 Kelvin. Robust & durable design capable of operating for an extended period of time. Ion densities comparable to pulsed sources Increased sensitivity! Plans for improving this design will be tested by studying the ν1 fundamental band of HN2+.

Acknowledgments For more information visit the McCall Research Group at http://bjm.scs.uiuc.edu