The Performance Of A Continuous Supersonic Expansion Discharge

Source

Carrie A. Kauffman, Kyle N. Crabtree, Benjamin J. McCall

Department of Chemistry, University of IllinoisJune 24th, 2010

Outline1. Motivation 2. Source Design

3. Results 4. Conclusion

Motivation

Motivation

Interstellar medium:Diffuse Molecular Clouds

Temp ~ 60 KDensity ~ 101–103 cm-3

Dense Molecular CloudsTemp ~ 20 KDensity ~ 104–106 cm-3

Sensitive Cooled Resolved Ion BEam Spectroscopy

For more on SCRIBES, please stay for RE06.

Production of Cold Molecular Ions

Trot ~ 110-180 K

Trot ~ 300+ 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

High Pressure Gas

Small Orifice Trot ≈ 5-30 K

Low Pressure

Continuous Supersonic Expansion Discharge Source

Leybold 3-Stage Pumping SystemPumping speed ~ 3600 L/s

Basic Design

Anode

Macor Spacer

Cathode

Macor Cap

Gas InputHigh Temp

Silicone O-rings

H3+

R(1,0) R(1,1)u R(2,2)l

McCall, B.J. Ph.D. Thesis, University of Chicago, 2001.

Rotational Constant:43.56 cm-3

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

• ↑ column density with increasing discharge current.

•↑ in rotational temperature with increasing discharge current.

•Operated for over 150 hours without source failure.

Low Current Regime

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

Not Reported 1 x 1011 5x1010

3. Davis et al. Chem. Phys. Lett. 2001, 344, 23-30.

1. Xu et al. Chem. Phys. Lett. 1995, 242 126-131.

2. Tom et al. J. Chem. Phys. 2010, 132, 081103.

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