1. 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 Benjamin J. McCall, Departments of Chemistry and Astronomy, University of Illinois at Urbana-Champaign

2. Why study C 60 ? Figure from:J. Cami, J. Bernard-Salas, E. Peeters, and S.E. Malek. Science 329, 1180 (Sep. 2010) {2} SymmetryAstrochemical Relevance

3. How do we look for C 60 ? Figures from:B. Brumfield. Development of a quantum cascade laser based spectrometer for high-resolution spectroscopy of gas phase C 60. UIUC, 2011. {3} High- temperature ( ~ 850 K) oven Cooling via continuous supersonic expansion CW-CRDS detection, ~ 1185 cm -1 C 60 Vapor Pressure

4. What do we expect to see? Figure from:J. T. Stewart, B. Brumfield, B. M. Gibson, B. J. McCall. In preparation. {4} ∆B

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

6. 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 C 60. UIUC, 2011. {6} High-Temperature Oven AlignmentGround State Population

7. Do other molecules cool efficiently? {7} Pyrene Oven temp ~ 430 K Estimated from absorption depth T vib 60-90 K D2OD2O Oven temp ~ 800 K Estimated from hot band T vib > 1000 K

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

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

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

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

12. How does vibrational cooling work? See also:M. E. Sanz, M. C. McCarthy and P. Thaddeus. J. Chem. Phys. 122, 194319 (2005) {12} Intermode Relaxation BendStretch

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

14. 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) {14} Laser Ablation Initial temperature >1900K Laser Desorption Initial temperature uncertain Ground state detectable by R2PI

15. How can we produce colder vapor? See also:C. H. Sin, M. R. Linford, and S. R. Goates. Anal. Chem. 64, 233 (1992) {15} Supercritical Fluid Expansion Initial temperature solvent dependent ( ~ 450 K) CO 2 w/ toluene co-solvent – aids cooling Low vapor flux ( ~ 10 13 molecules s -1 )

16. Conclusions {16} C 60 signal not yet observed Lack of signal likely due to poor vibrational cooling Efficient cooling highly dependent upon initial temperature New vaporization technique required

17. Acknowledgements {17} McCall Group Brian Brumfield Claire Gmachl