1. Progress In The Development Of An Infrared Ion Beam Spectrometer

2. Outline Why molecular ion beam First generation SCRIBES instrument
Improvements
Development of the second generation SCRIBES
Prospects
Sensitive
Cold
Resolved
Ion
BEam
Spectrometer

3. Why Use Molecular Ion Beam?
Why molecular ions
Astrochemistry
Combustion
Carbocation chemistry
Fundamental insterest
Δω depends on √1/Ufloat voltage
Why fast ion beam
Kinematic compression
High resolution spectroscopy
Fingerprint for molecular ions
Andrew Mills, WH02 at 2:05pm

4. First Generation SCRIBES Instrument
Modular
Electron Multiplier
Low ion beam current
Overlap of the laser
Anode
Development of TOF-MS
Cathode
Iris
Pulser Plate
Ion Optics
Ringdown Mirrors
InSb
Ion Optics
Drift Region
Quadrupoles
Modeled after Saykally’s instrument (Saykally et al. J. Chem. Phys. 1989, 90 (8), )

5. Second Generation SCRIBES
Source
Modular instrumentation
High ion beam current
Improved ion optics
Differential pumping

6. Ion Sources Considerations for the test application High ion density
Fast ion beam without a big energy spread
Low maintenance
Supersonic source
Cold cathode discharge source
Rotationally cold ions
Continuous source
Modular
Precursor gas
Anode
Cathode
Fused Silica

7. Uncooled Cold Cathode Source with N2 Plasma
3.5 kV
Anode
7.5 kV
Extraction plate
Ground
N2 plasma
ISource = 30 µA
IBeam = 10 µA
IOverlap = 1.5 µA

8. Ion Optics
Einzel Lens
Side view
Frontal view

9. Cavity Region V- V+
Neutrals
Laser path
Ions only
3 mm
3 mm

10. Quadrupoles
Output
Input +V -V
Collimated beam +V -V
Diverging beam

11. Asymmetrical Deflector Plates
Output
parallel beam
Input
focused beam
(+)V
(-)V

12. Mass Selecting Region Identity of the masses Beam energy
Beam energy spread
Characterization method
TOF mass spectrometer
The new instrument is modular therefore working with different setup have become quite easy. We have moved to a CF system instead of chambers. We are able to profile the ion beams character on horizontal and vertical axis using BPMs, Apertures helps in overlapping the laser beam with the ion beam with better precision that prior instrument and also these apertures defines a highly collimated beam. Our mass spectrometer is also to easy to separate from the instrument. We also have faraday cups located at several positions to measure beam current as well as to trouble shoot any problems.
We were lacking higher ion beam current from the source. We decided to keep the source from first generation SCRIBE instrument due to its simplicity. However we instrooduced better ion optics and differential pumping to improve the ion current.
In the old instrument the cavity region was defined by the use of quadrupoles. Main problem with these was the fact we were unable to create a collimate ion beam and the overlap of the laser was ambiguous. Current setup has a bender to divert the ion beam off the source pathway, this works better than the quadrupole in creating a collimated beam. These small spertures help in alingment of the laser to the ion beam.
First generation SCRIBE never made it to the mass spectrometer development, we full filled that dream in the second generation instrument to characterize the beam.
Time-of-Flight Mass Spectrometer

13. Laser
Collision Cell
CO2 gas at 30 mTorr
Ringdown mirror

14. Mass Spectrometer

15. Mass Spectrum of N2 Plasma
Ion beam energy = 3580 V ± 10 V
Power supply output = 3574 V

16. Ion modulated cavity ringdown spectroscopy
Growth of SCRIBES
Velocity modulated
cavity enhanced spectroscopy
cw-Cavity ringdown spectroscopy
Supersonic
source
H3+ band (fundamental)
Ion modulated cavity ringdown spectroscopy
2st Generation
SCRIBES
1st Generation
SCRIBES
Test N2+ Meinel lines
DFG laser

17. Acknowledgement
McCall Group
Funding

18. Questions?