mid-ir direct absorption/dispersion spectroscopy of a fast ion beam
DESCRIPTION
Mid-IR Direct Absorption/Dispersion Spectroscopy of a Fast Ion Beam. Brian Siller Michael Porambo Benjamin McCall. Near-IR Work. N 2 + is a good test molecule Not much else in the near-IR. Mid-IR Motivation. Astrochemistry >160 Molecules observed in ISM Only ~20 are ions - PowerPoint PPT PresentationTRANSCRIPT
Mid-IR Direct Absorption/Dispersion Spectroscopy of a Fast Ion BeamBrian SillerMichael PoramboBenjamin McCall
Near-IR Work• N2
+ is a good test molecule• Not much else in the near-IR
• Astrochemistry– >160 Molecules observed in ISM– Only ~20 are ions
• Fundamental Physics– CH5
+
– Carbocation reactive intermediates
Mid-IR Motivation
H2+
H3+
CH+
CH2+
CH3+
CH5+
CH4
C2H3+
C2H2
C3H+
C3H3+
C4H2+
C4H3+
C6H5+
C6H7+ C6H6
H2
H2
H2
H2
H2
C
e
C+
e
C+
C
H
C2H2
H2
e
OH+H2O+
H3O+H2O
OHe
OH2
H2
HCO+
CO
HCNCH3NH2
CH3CN
C2H5CN
N, eNH3, e
HCN, eCH 3CN, e
eCO, e
H2O, e
CH3OH, e
CHCH2CO
CH3OH
CH3OCH3
CH3+
C2H5+e
C2H4
eC3H2
eC3H
eC2H
CH5+
From White et al. Science, 1999, 284, 135–137.
Ti:Sapph Laser
PolarizingBeamsplitter
QuarterWave Plate
AOM
Locking Electronics
Ion BeamInstrument
PZT
20MHz
EOM1 EOM2
113MHz
AbsorptionSignal
Lock-In Amplifier
40 kHzDrift Tube
Modulation
DispersionSignal
Lock-In Amplifier
CavityModes
LaserSpectrum
ExperimentalSetup
fastslow
CavityModes
LaserSpectrum
Ion BeamInstrument
Ti:Sapph Laser
Nd:YAG Laser
EOM1 EOM2
PPLN
AOM
RAM: Residual Amplitude Modulation
NICE-OHMS Implementations
• Near-IR (0.7-1.7µm)– Nd:YAG1
– Ti:Sapph2
– ECDL3
– EDFL4
• Mid-IR (8.5µm)– QCL5
• Our DFG system represents the first* broadly tunable mid-IR NICE-OHMS spectrometer*see talks WI06 and WI07 on our OPO-based system for the other “first” of this kind
1J. Ye, et al., JOSAB 15, p.6 (1998) 2L. Ma, et al., JOSAB 16, p.2255 (1999) 3C. Ishibashi, et al., J. Mol. Spec. 200, p.147 (2000) 4F. Schmidt, et al., JOSAB 24, p.1392 (2007) 5M. Taubman, et al., Spectrochim. Acta A 60, 3457 (2004)
Spectroscopy Characterization
• The first broadly tunable mid-IR NICE-OHMS system (2.8-4.8 µm)
• Doppler broadened methane
Absorption
Dispersion
30mW coupled into cavity
Finesse ~ 300
Saturation parameter ~ 14
Sub-Doppler Spectroscopy• wm-NICE-OHMS of methane• ~3 MHz dither, 1f detection
Absorption
Dispersion
Sensitivity Analysis• fm-NICE-OHMS: 7×10-9 cm-1
• wm-NICE-OHMS: 8×10-10 cm-1
Frequency Calibration
• Calibrate Ti:Sapph with frequency comb
• Lock Nd:YAG to I2 hyperfine transition
Ion Beam Integration
H2+
H3+H+ H2
+
H3+
H+
Δt ~ 4 nsΔE ~ 4 VΔν ~ 70 MHz
+7 kV +4 kV 0 kV
Cathode in Front
+1 kV +4 kV 0 kV
Anode in Front
N+
N2+
NOCollisions!H2
+ + H2 → H3+ + H
Future Work• Obtain and optimize H3
+ absorption signal• Supersonic expansion discharge source
• 750 K rotational temperature with cold cathode• <100 K with supersonic source
• Vibrational spectroscopy of rotationally cooled molecular ions (CH5
+, C3H3+, etc.)
Crabtree, K. N. et al. Rev. Sci. Instrum. 2010, 81, 086103.
AcknowledgmentsMcCall Research Group
Jessica PearsonJoe PuhrCraig Riccardo
FundingNSF NASAAir Force PackardDreyfus Sloan