1. 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

2. 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

3. 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

4. Experimental Design – LIF and Chirped Pulse mmW
Standard Pulsed Valve (Argon)
Hanging Wire
Sample Cup
Heating coil
Vacuum Chamber: 40 μtorr

5. Experimental Design – LIF and Chirped Pulse mmW
Standard Pulsed Valve (Argon)
Hanging Wire
Heat
Sample Cup
Heating coil
Vacuum Chamber: 40 μtorr

6. 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

7. 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

8. 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).

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. ✔ ✗ 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.

17. 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

18. Acknowledgements Prof. Robert Field Dr. Carrie Womack Jun Jiang
Trevor Erickson
Cummins Group
Matt Nava
Funding: U.S. Department of Energy
DOE funding