progress in the development of an infrared ion beam spectrometer

Main Title

Kyle Crabtree, Kyle Ford, Holger Kreckel, Andrew Mills, Manori Perera and Ben McCall

University of Illinois at Urbana-Champaign

64th International Symposium on Molecular SpectroscopyOhio State University

June 23th, 2009

Progress In The Development Of An Infrared Ion Beam

Spectrometer

Progress In The Development Of An Infrared Ion Beam

Spectrometer

2

OutlineOutline

• Why molecular ion beam

• First generation SCRIBES instrument

• Improvements

• Development of the second generation SCRIBES

• Prospects

SensitiveColdResolvedIonBEamSpectrometer

3

Why Use Molecular Ion Beam?

Why Use Molecular Ion Beam?

• Why molecular ions• Astrochemistry• Combustion • Carbocation chemistry• Fundamental insterest

• Why fast ion beam• Kinematic compression

• High resolution spectroscopy• Fingerprint for molecular ions

Andrew Mills, WH02 at 2:05pm

Δω depends on √1/Ufloat voltage

200

150

100

50W

idth

of th

e ab

sorp

tion

lin

e (M

Hz)

10008006004002000

Beam voltage (V)

4

First Generation SCRIBES Instrument

First Generation SCRIBES Instrument

Cathode

Anode

Ion Optics

Quadrupoles

Ion Optics

Pulser Plate

Iris

Electron Multiplier

Ringdown Mirrors

InSb

Drift Region

Modeled after Saykally’s instrument (Saykally et al. J. Chem. Phys. 1989, 90 (8), 3893-3894)

• Low ion beam current

• Overlap of the laser

• Modular

• Development of TOF-MS

5

Second Generation SCRIBESSecond Generation SCRIBESSource

• High ion beam current• Improved ion optics• Differential pumping

• Modular instrumentation

6

Ion Sources Ion Sources

• Cold cathode discharge source

• Considerations for the test application• High ion density• Fast ion beam without a big energy spread• Low maintenance

Precursor gas

Anode Cathode

Fused Silica

• Supersonic source

• Rotationally cold ions

• Continuous source

• Modular

7

Uncooled Cold Cathode Source with N2 PlasmaUncooled Cold Cathode Source with N2 Plasma

Source Cathode3.5 kV

Anode7.5 kV

Extraction plateGround

N2 plasma

ISource = 30 µA

IBeam = 10 µA

IOverlap= 1.5 µA

8

Ion OpticsIon Optics

Einzel Lens

Side view Frontal view

9

Cavity RegionCavity Region

V-V+

Neutrals

Laser path

Ions only3 mm

3 mm

10

QuadrupolesQuadrupoles

Output Input

Collimated beam

-V

+V

+V

-V

Diverging beam

11

Asymmetrical Deflector Plates

Asymmetrical Deflector Plates

Output parallel beam

Inputfocused beam

(-)V

(+)V

12

Mass Selecting RegionMass Selecting Region

• Characterization method• TOF mass spectrometer

Time-of-Flight Mass Spectrometer

• Identity of the masses

• Beam energy

• Beam energy spread

13

Collision CellCollision Cell

Laser

Rin

gdow

n T

ime

Con

stan

t (µ

s)

Pseudo-time (s)

CO2 gas at 30 mTorr

Ringdown mirror

14

Mass SpectrometerMass Spectrometer

8

6

4

2

Inte

nsi

ty (m

V)

353025201510

Mass (amu)

N+

O+

H2O+

N2+

O2+

15

Mass Spectrum of N2 PlasmaMass Spectrum of N2 Plasma

Ion beam energy = 3580 V ± 10 V

Power supply output = 3574 V

8

6

4

2

0

Inte

nsi

ty (V

)

30252015Mass (amu)

N2+ (m/z=28)90%

N+ (m/z=14)10%

16

Growth of SCRIBESGrowth of SCRIBES

1st Generation SCRIBES

cw-Cavity ringdown spectroscopy

2st Generation SCRIBES

Test N2+

Meinel lines

Velocity modulated cavity enhanced spectroscopy

Ion modulated cavity

ringdown spectroscopy

DFG laser

H3+ band

(fundamental)

Supersonic source

17

AcknowledgementAcknowledgement

• McCall Group

• Funding

Questions?Questions?