Diiodomethane in Strong Laser Pulses Kyle Jensen Mentors Dr Artem Rudenko and Dr Daniel Rolles Kansas State University Motivation Halomethanes are a hot topic within atmospheric chemistry ID: 916450
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Slide1
Coulomb Explosion Imaging and Ionization of Diiodomethane in Strong Laser Pulses
Kyle JensenMentors: Dr. Artem Rudenko and Dr. Daniel RollesKansas State University
Slide2Motivation
Halomethanes are a hot topic within atmospheric chemistryHalomethanes provide a source of reactive halides leading to ozone destructionS. R. Nichols, “Strong field dynamics and control of molecular dissociation
”, PhD Thesis, Stony Brook University, 2008.In particular, diiodomethane (CH
2
I
2) represents a good test system for studies of atomic motion in molecules triggered by light: dissociation, vibrations, …D. Geißler, B.J. Pearson and T. Weinacht, „Wave packet driven dissociation and concerted elimination in CH2I2”, J. Chem Phys. 127 204305 (2007).The main goal of this project: create a “movie” of the molecule either vibrating or breaking apart (dissociating).
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Slide3Overview
BackgroundA Concept of the Pump-Probe ExperimentExperimental SetupResultsSummary and Outlook
3
Slide44
A “snapshot” of molecular motion
Pump pulse excites vibrations (rotations, dissociation, etc…
Distance between the fragments is reconstructed from the measured fragment energies:
Probe pulse removes two electrons from the two nuclei, and the molecule “explodes” due to the Coulomb repulsion: “
Coulomb explosion imaging”
molecule
Pump-Probe Concept
Slide5Experimental Setup
5
Interferometer
COLTRIMS:
A “Reaction Microscope”
for ions
Laser
Slide6Mach-Zehnder Interferometer
6
Slide7COLTRIMS
Cold target recoil ion momentum
spectroscopyDetects resulting ions and electrons after ion/photon interactions with a gas target (measures mass to charge ratios, kinetic energies and emission angles
)
Provides insight for a target’s potential dissociation channels
C. M. Maharjan, “Momentum imaging studies of electron and ion dynamics in a strong laser field”, PhD Thesis, Kansas State University, 2007.710-6
10-4
10
-9
10
-11
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Laser
---
Gas JetE,B
Slide8COLTRIMS
Main componentsGas jetUltrahigh vacuum chamberPressure: 10-11 torr
Differential pumping stagesSpectrometer
Time- and
Position Sensitive
Detector (MCP + Delay line)Focusing mirror (not shown)Laser directed into vacuum from the back810-6
10
-4
10
-9
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Laser
---
Gas Jet
1
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4
5
Slide9Experimental Specifications
Pulsar Laser Specs25 fs pulseWavelength: 800 nmRepetition Rate: 10 kHzIntensity:
Molecule: CH
2
I
2Ionization Potential: 9.34 eVVapor Pressure: 141 torrVibrational period (bending): ~300 fs 9
Diiodomethane (CH2I
2
)
~300 fs
Slide10Data AnalysisCalibrate Time of Flight (
ToF) spectra(define mass to charge ratios)Classify potential dissociation channels and measure fragment energiesAnalyze the ion yields and kinetic energy release (KER) as a function of pump-probe delay
10
Slide11ToF Ion Calibration
11
Slide12ToF Spectrum
12
CH2I
2
++
I2+
CH
2
+
CH
2
I
+
I
+CH
2I2+H2O+I++
Slide13Classification of Dissociation Channels: Ion-Ion Coincidence Spectrum
13
CH2
I
+
+I+
Slide1414
~300 fs
- I
+
CH
2
I+
I
2
+
CH
2
I
2
+
Delay / fsNormalized ion yieldDelay-dependent yields of different fragments300 fs: bending vibrations!
Slide1515
~300 fs
~300 fs
Enlarged view of the CH
2
I
+
channel
Slide1616
Delay
(
fs)
KER
(eV)Delay-dependent KER of CH2I+ + I+ coincident channel
Bound molecule
Dissociating molecule
Conclusions and OutlookWe have measured the ionic fragments after ionization, dissociation and Coulomb explosion of CH
2I2 molecule in a pump-probe experimentWe observe bending vibrations of the molecule and mapped one of the dissociation pathwaysIn the future, this technique will be applied to study different light-induced reactions in similar molecules
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Slide18AcknowledgementsThis material is based upon work supported by National
ScienceFoundation Grant: NSF grant number PHYS-1461251Dr. Artem RudenkoDr. Daniel Rolles
Lee PearsonBalram KaderiyaFarzaneh
Ziaee
Raju
Pandiri18