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Detection of HCP Thermolyzed from a Stable Synthetic Precursor
Alexander W. Hull, Jun Jiang, Trevor J. Erickson, Carrie Womack, Matthew Nava, Christopher Cummins, Robert W. Field MIT Department of Chemistry Abstract Names
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Interest in HCP: A Spectroscopist’s Perspective
Similar to HCN, traditionally a more chemically relevant molecule: A(bent) — X (linear) transition The bending normal mode has a double potential well, corresponding to HCN/HNC or HCP/HPC isomerization Difference: HCP A — X transition is more accessible than the HCN A — X transition. Energy Diagram of double potential well Bending Vibrational Coordinate
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Interest in HCP: A Synthetic Chemist’s Perspective
Collaboration with the Cummins Group at MIT: Goals: Confirm that this precursor thermalizes to produce HCP Use the vibrational temperatures to gain insight into the mechanism Heat (200 C) Solid Solid Gas Stable under nitrogen
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Experimental Design – LIF and Chirped Pulse mmW
Standard Pulsed Valve (Argon) Hanging Wire Sample Cup Heating coil Vacuum Chamber: 40 μtorr
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Experimental Design – LIF and Chirped Pulse mmW
Standard Pulsed Valve (Argon) Hanging Wire Heat Sample Cup Heating coil Vacuum Chamber: 40 μtorr
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Experimental Design – LIF and Chirped Pulse mmW
Standard Pulsed Valve (Argon) Hanging Wire Pulse or Continuous Flow of Ar Sample Cup Heating coil Vacuum Chamber: 40 μtorr
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Experimental Design – LIF and Chirped Pulse mmW
Standard Pulsed Valve (Argon) Interrogate with either: Hanging Wire Pulse or Continuous Flow of Ar Chirped Pulse mmW or Laser Induced Fluorescence (LIF) Sample Cup Heating coil Vacuum Chamber: 40 μtorr
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LIF Chirped Pulse mmW G.B. Park, A.H. Steeves, K. Kuyanov-Prozument, J.L. Neill, R.W. Field 135, (2011) . Fast, broadband, high resolution technique ( GHz) Potential to monitor multiple rotational transitions at once For this initial experiment, we were probing the (v = 0) J = 2-1 pure rotational transition at MHz. J. W. C. Johns, J. M. R. Stone, and G. Winnewisser, J. Mol. Spectrosc. 38, 437 (1971). Excite with a tunable laser Detect the resulting fluorescence using a photomultiplier tube Probing the well characterized A(0311) – X(0000) vibronic transition J. W. C. Johns, H. F. Shurvell, and J. K. Tyler, Can. J. Phys. 47, 893 (1969).
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Chirped Pulse mmW: Why Broadband is Useful in this Context
V = 0 J = 2 - 1 v = 1 J = 2 - 1 Comparing intensity of the J = 2 – 1 rotational transitions of the v = 0, v = 1, v = 2 vibrational levels gives the population of each vibrational level v = 2 J = 2 - 1
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Results 6 different experiments:
Supersonic expansion into 40 μtorr vacuum with chirped pulse detection Supersonic expansion into 40 μtorr vacuum with LIF detection Continuous HCP production at ~1 mtorr with chirped pulse Continuous HCP production at ~1 mtorr with LIF Continuous HCP production at 100 mtorr with chirped pulse Write pressures: (40 microtorr) Continuous HCP production at 100 mtorr with LIF
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Results 6 different experiments:
Supersonic expansion into 40 μtorr vacuum with chirped pulse detection Supersonic expansion into 40 μtorr vacuum with LIF detection Continuous HCP production at ~1 mtorr with chirped pulse Continuous HCP production at ~1 mtorr with LIF Continuous HCP production at 100 mtorr with chirped pulse Write pressures: (40 microtorr) Continuous HCP production at 100 mtorr with LIF
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Results 6 different experiments:
Supersonic expansion into 40 μtorr vacuum with chirped pulse detection Supersonic expansion into 40 μtorr vacuum with LIF detection Continuous HCP production at ~1 mtorr with chirped pulse Continuous HCP production at ~1 mtorr with LIF Continuous HCP production at 100 mtorr with chirped pulse Write pressures: (40 microtorr) Continuous HCP production at 100 mtorr with LIF
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Results 6 different experiments:
Supersonic expansion into 40 μtorr vacuum with chirped pulse detection Supersonic expansion into 40 μtorr vacuum with LIF detection Continuous HCP production at ~1 mtorr with chirped pulse Continuous HCP production at ~1 mtorr with LIF Continuous HCP production at 100 mtorr with chirped pulse Write pressures: (40 microtorr) Continuous HCP production at 100 mtorr with LIF
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Results 6 different experiments:
Supersonic expansion into 40 μtorr vacuum with chirped pulse detection Supersonic expansion into 40 μtorr vacuum with LIF detection Continuous HCP production at ~1 mtorr with chirped pulse Continuous HCP production at ~1 mtorr with LIF Continuous HCP production at 100 mtorr with chirped pulse Write pressures: (40 microtorr) Continuous HCP production at 100 mtorr with LIF That only the flooded chamber with LIF worked suggests low HCP number density
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Temperature of the above spectrum: ~ 300 K
LIF A(0311) - X(0000) Band (100 mtorr) Scan cm-1 Assignments from: J. W. C. Johns, H. F. Shurvell, and J. K. Tyler, Can. J. Phys. 47, 893 (1969). Rotational temperature was estimated by comparing the relative intensities of 3 nearby peaks to simulated spectra Temperature of the above spectrum: ~ 300 K Exponential decay Lump: number density/laser fluctuations
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✔ ✗ Goals: Confirm that this precursor thermalizes to produce HCP
Determine the vibrational temperatures and use them to infer mechanism ✔ ✗ We had to flood the chamber, so we lost all information regarding mechanism.
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Indentation for Holding Sample
Moving Forward: We need a method that achieves high number density of HCP molecules that haven’t equilibrated with the walls of the chamber. Best option is (gentle) laser ablation Another option (higher number density only): Hole Pulsed Valve Indentation for Holding Sample c c
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Acknowledgements Prof. Robert Field Dr. Carrie Womack Jun Jiang
Trevor Erickson Cummins Group Matt Nava Funding: U.S. Department of Energy DOE funding
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