Transcript Neutral-ion collisions in merged beams experiments

High Resolution Spectroscopy of Molecular Ion Beams
Holger Kreckel, Andrew Mills, Manori Perera,
Brian Siller, Kyle Crabtree, Carrie Kauffman,
Benjamin J. McCall
University of Illinois at Urbana-Champaign
SCRIBES
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Upcoming observatories exploring the molecular universe
Herschel
Space Observatory
SOFIA
Stratospheric Observatory for Infrared Astronomy
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Interstellar Medium: density and temperature
Molecular clouds:
places of stellar birth
temperatures:
density:
10-100 K
102 - 108 cm-3
• no three-body collisions
• no endothermic reactions
• no reactions with barriers
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Ions are key!
- the UMIST database lists 4572 binary reactions,
2386 ion-neutral reactions,
552 charge exchange reactions,
- 2/3 of the reactions are ion-neutral processes,
- 30% of these reactions have been measured.
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Ion
Spectroscopy
Techniques
Hirota, Amano
Maier, Nesbitt
Velocity
Modulation
Hollow
Cathode
Supersonic
Expansion
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Oka, Saykally
High ion column density
Ion-neutral discrimination
Low rotational temperature
Narrow linewidth
Compatible with
cavity-enhanced spectroscopy
Mass spectrometry of laser-probed ions
Spectral identification of ion mass
Sensitive
Cooled
Resolved
Ion
BEam
Spectroscopy
SCRIBES
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ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Why Ion Beam Spectroscopy?
kinematic compression
of the linewidth
Δω ~ 1/√ Ebeam
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
SCRIBES setup
detector
supersonic
expansion
source
20 cm
ion beam
cavity
mirrors
Overlap region
beam modulation plates
TOF mass spectrometer
laser light
particle
detector
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Ion sources
Cold cathode
discharge
Cathode
3.5 kV
Extraction plate
Ground
Continuous
Supersonic
Expansion
Anode
7.5 kV
N2 plasma
• simple
• high ion density
• rotationally hot
• new development
• requires heavy pumping
• rotationally cold
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Continuous supersonic expansion source
(K Crabtree, C Kauffman)
O-Rings
3 atm
Pinhole
Gas flow
<100
mtorr
Anode
Cathode
Macor Spacer
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Ion optics
Goal: optimize ion density in the overlap region
ion beam
20 cm
ion
source
Overlap region
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Quadrupole vs. asymmetric cylindrical deflector
Electrostatic quadrupoles are often used as 90o deflectors
-V
+V
Collimated beam
+V
-V
Diverging beam
Output
Input
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Asymmetric cylindrical deflector
R1=140 mm
V1=-740 V
z
y
x
R2=178 mm
V2=+740 V
y
y
x
z
z
z
3 keV ion beam
vacuum chamber
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Asymmetric cylindrical deflector
xxxxxxxxxx
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Ion optics
Goal: optimize ion density in the overlap region
Performance with the
cold cathode source:
ion beam
20 cm
ion
source
Overlap region / 30 cm
ISource = 30 µA
IBeam = 10 µA
IOverlap = 2 µA
(confined by 4mm
apertures,13 cm apart)
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Time of Flight Mass Spectrometer
(M Perera)
Goal: characterize ion beam: composition, energy, energy spread
ion beam
20 cm
ion
source
Overlap region
beam modulation plates
TOF mass spectrometer
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Time of Flight measurements
N+
Beam energy
width
~2ns
Voltage
TOF
energy
spread ~ 2V
N2+
3510V
3560V
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
SCRIBES setup
Source
chamber
TOF Mass
spectrometer
Overlap
region
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Spectroscopy: first tests with N2+
cw cavity ringdown spectroscopy (cw-CRDS)
detector
Ti:Sa @ 925 nm
Source chamber
Optical Isolator
l-meter
Etalon
Finder
FPI
AOM
apertures
Mode
Matching
Optics
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Concentration Modulation CRDS
•99.99% RD Mirrors
33 ms time constant
amin =4x10-9 cm-1
•Concentration Modulation
Beam on/ Beam off
amin =5x10-10 cm-1
Reduces long term Drift
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
CRDS / representative scans N2+
-9
x10 (cm-1)
Absorbance
x10-9
amin=4.5 x 10-10 cm-1
20
1.0
15
0.8
10
0.6
5
0.4
0
-5
0.2
-10
924.405
924.406
924.407
924.408
Wavelength (nm)
924.409
924.410
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Next step: velocity modulation
(A Mills, B Siller)
detector
pzt
Source chamber
• Use lower finesse
cavity
• Modulate the velocity
of the ion beam by
applying field to drift
region
PLL
apertures
• Use lock in detection
to further reduce noise
and increase signal
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Cavity enhanced velocity modulation
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Cavity enhanced velocity modulation
Siller, B, Mills, A, and McCall B.J., Optics Letters, accepted
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
SCRIBES / Spectroscopy with Molecular Ion Beams
Future: high resolution infrared spectroscopy
difference frequency generation laser (DFG) 2.8- 4.8 µm
ortho-H3+
para-H3+
Nd:YAG
1064 nm
l/4
l/2
AOM
532 nm
pump
laser
Ti:Sapph
700 – 990 nm
reference
cavity
PPLN
detector
2.8 – 4.8 μm
l/2
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
SCRIBES / Spectroscopy with Molecular Ion Beams
Future: high resolution infrared spectroscopy
Menlo Systems frequency comb
Source: NIST
Source: Menlo Systems
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Lock-in-signal
Precision Cavity Enhanced Velocity
Modulation of N2+ in a AC Discharge Plasma
4
Q22(14)
6.6
6.4
6.2
0.001 cm-1
Ferguson
6.0
3
85
MHz
CEVMS
2
5.8
5.6
1
5.4
5.2
0
10859.34000
10859.34500
cm-1
10859.35000
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
High resolution Spectroscopy with SCRIBES
Almost all the individual parts are working,
Now we have to bring them all together!
Velocity modulation
Expansion source
DFG Laser
HNN+, HCS+,HOC+,
HCO+, CO+,CH+,
SCRIBES
+, CH +,
HCNH
5
+
C3H3 , C6H7+
etc, etc ....
Frequency
comb
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Acknowledgements
NSF Division of
AMO Physics
Dreyfus New
Faculty Award
NASA Laboratory
Astrophysics
NSF Divisions of
Chemistry & Astronomy
Holger Kreckel, Andrew Mills,
Manori Perera, Brian Siller,
Kyle Crabtree, Carrie Kauffman,
Benjamin J. McCall
University of Illinois
at Urbana-Champaign
Packard
Fellowship
Air Force Young
Investigator Award
Cottrell
Scholarship
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Action spectroscopy of H3+ in a cryogenic ion trap
He, Ar
H3+
H3+
ArH+
ArH++H2 - 0.57 eV
E [cm-1]
detector
H3+ (v=0) +Ar
H3+ (v>1) + Ar
ArH+ + H2 + X eV
Ti:Sa Laser
α [rad]
Kreckel et al, JCP 129, 164312 (2008)
ACS San Francisco, Mar 22nd 2010
Holger Kreckel / UIUC
High Resolution Spectroscopy of Molecular Ion Beams
Ion
Spectroscopy
Techniques
Hirota, Amano
Maier, Nesbitt
Velocity
Modulation
Hollow
Cathode
Supersonic
Expansion




()





Oka, Saykally
High ion column density
Ion-neutral discrimination
Low rotational temperature
Narrow linewidth
Compatible with
cavity-enhanced spectroscopy
Mass spectrometry of laser-probed ions
Spectral identification of ion mass
Sensitive
Cooled
Resolved
Ion
BEam
Spectroscopy
SCRIBES
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