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Vibrational cooling of large molecules in supersonic expansions: The case of C 60 and pyrene

Vibrational cooling of large molecules in supersonic expansions: The case of C 60 and pyrene. Bradley M. Gibson and Jacob T. Stewart, Department of Chemistry, University of Illinois at Urbana-Champaign

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Vibrational cooling of large molecules in supersonic expansions: The case of C 60 and pyrene

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  1. Vibrational cooling of large molecules in supersonic expansions: The case of C60and pyrene Bradley M. Gibson and Jacob T. Stewart, Department of Chemistry, University of Illinois at Urbana-Champaign Benjamin J. McCall, Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign

  2. Symmetry Astrochemical Relevance Why study C60? Figure from: J. Cami, J. Bernard-Salas, E. Peeters, and S.E. Malek. Science 329, 1180 (Sep. 2010)

  3. High- temperature (~850 K) oven • Cooling via continuous supersonic expansion • CW-CRDS detection, ~1185 cm-1 C60 Vapor Pressure How do we look for C60? Figures from: B. Brumfield. Development of a quantum cascade laser based spectrometer for high-resolution spectroscopy of gas phase C60. UIUC, 2011.

  4. Branch heads possible • S / N = • Pinhole nozzle: ~2 • Slit nozzle: ~40 What do we expect to see? ∆B Figure from: J. T. Stewart, B. Brumfield, B. M. Gibson, B. J. McCall. In preparation.

  5. Estimated: What did we actually see? Observed: (NEA ~0.6 ppm) Figures from: J. T. Stewart, B. Brumfield, B. M. Gibson, B. J. McCall. In preparation.

  6. Ground State Population High-Temperature Oven Alignment Why didn’t we see anything? Figure from: B. Brumfield. Development of a quantum cascade laser based spectrometer for high-resolution spectroscopy of gas phase C60. UIUC, 2011.

  7. Pyrene • Oven temp ~430 K • Estimated from absorption depth • Tvib 60-90 K • D2O • Oven temp ~800 K • Estimated from hot band • Tvib > 1000 K Do other molecules cool efficiently?

  8. V-T Transfer How does vibrational cooling work? v = 2 v = 1 kBT kBT v = 0 Translational Energy: ↑ Vibrational Energy: ↓ See also: M. E. Sanz, M. C. McCarthy and P. Thaddeus. J. Chem. Phys. 122, 194319 (2005)

  9. V-T Transfer How does vibrational cooling work? v = 2 kBT v = 1 kBT v = 0 Translational Energy: ↑ Vibrational Energy: ↓ See also: M. E. Sanz, M. C. McCarthy and P. Thaddeus. J. Chem. Phys. 122, 194319 (2005)

  10. V-T Transfer How does vibrational cooling work?

  11. Intramode Relaxation How does vibrational cooling work? v = 2 v = 1 v = 0 See also: M. E. Sanz, M. C. McCarthy and P. Thaddeus. J. Chem. Phys. 122, 194319 (2005)

  12. IntermodeRelaxation How does vibrational cooling work? Bend Stretch See also: M. E. Sanz, M. C. McCarthy and P. Thaddeus. J. Chem. Phys. 122, 194319 (2005)

  13. Cluster Predissociation How does vibrational cooling work? Bend Intermolecular Stretch See also: G. Ewing. Chem. Phys. 29, 253 (Apr. 1978)

  14. Laser Ablation • Initial temperature >1900K • Laser Desorption • Initial temperature uncertain • Ground state detectable by R2PI How can we produce colder vapor? See also: E. E. B. Campbell, I. V. Hertel, Ch. Kusch, R. Mitzner, and B. Winter. Synth. Mat. 77, 173 (1996) R. E. Haufler, L-S. Wang, L. P. F. Chibante, C. Jin, J. Conceicao, Y. Chai, and R. E. Smalley. Chem. Phys. Lett. 179, 449 (1991)

  15. Supercritical Fluid Expansion • Initial temperature solvent dependent (~450 K) • CO2 w/ toluene co-solvent – aids cooling • Low vapor flux (~1013molecules s-1) How can we produce colder vapor? See also: C. H. Sin, M. R. Linford, and S. R. Goates. Anal. Chem. 64, 233 (1992)

  16. C60 signal not yet observed • Lack of signal likely due to poor vibrational cooling • Efficient cooling highly dependent upon initial temperature • New vaporization technique required Conclusions

  17. McCall Group • Brian Brumfield • Claire Gmachl Acknowledgements

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