Sanghamitra Deb, Michael P. Minitti, Peter M. Weber Department Of Chemistry Brown University 64 th OSU International Symposium on Molecular Spectroscopy hv June 26 th 2009

Hydrogen atom: Electron is moving in Coulomb potential created by proton Energy levels: Molecular Rydberg states: Rydberg states are analogous to the states of hydrogen atom The Rydberg electron is moving in the potential created by the molecular ion Energy levels: Rydberg States δ – quantum defect accounts for the shielding created by the molecular ion core 1Kuthirummal, N.; Weber, P. M., J. Mol. Struc. 2006, 787, 163 R Ryd = 13.6 eV – Rydberg Constant n – principal quantum number

Effects of clustering on Rydberg states How the clusters change the photoelectron spectrum Study the dynamics of clusters What are the changes in mass spectrum What are effects on the time dependence of the mass peaks 2 Goal

3 3s 3p Ion X e-e- e-e- 209 nm 418 nm E B (3p) E B (3s) Gosselin, J. L.; Minitti, M. P.; Rudakov, F. M.; Sølling, T. I.; Weber, P. M. J. Phys. Chem. A, 2006, 110, DMIPA (N,N-dimethylisopropylamine)

Ti:Sapphire Regenerative Amplifier Laser System Experiment BBO Crystals 418 nm 209 nm Ion MCP e - MCP Delay Stage 4 5 kHz Rep. Rate 209 nm pump (5.93 eV) 418 nm probe (2.96 eV) ~ 260 fs 4ω pulse width Cheng, W.; Kuthirummal, N.; Gosselin, J. L.; Sølling, T. I.; Weinkauf, R.; Weber, P. M. J. Phys. Chem. A 2005, 109, 1920.

3s 3p 3s 3p Cluster DMIPA PES 5 Sample condition: 5 torr (-30C) and 35 torr (0C) Carrier Gases: He and Ar Time Constants: 3p Decay : 670 fs(30 fs) 3s Rise : 670 fs (30 fs) 3s Decay : 67 ps (3 ps)

Fragment Parent Fragment Parent Dimer Trimer Higher Order Clusters Clusters Parent and Fragment DMIPA Mass Spec 6

Time Resolved Parent Peak 7 Two components of Mass-88 incase of Ar Higher isotope of parent Protonated Parent Two main questions How do we get protonated parent? On which surface it is generated? Mass = 88 Parent (Mass=87)

Model – He Data 8  Monomer: 3p 3s Pump Probe P+P+ P+P+ P + F + P (3s) P (3p) Time Constants 3σ Parent Decay650 fs12 fs Fragment Rise650 fs12 fs Fragment Decay67 ps3 ps

9  Dimer: 3p 3s Pump Probe D+D+ D+D+ D + PH + P+P+ P+P+ D (3s) P (3s) D (3p) Model – Ar Data

Parent Decay Parent Rise Higher Isotope of Parent ~ 5.6% Protonated Parent Decay Time Constants 3σ Parent Decay670 fs12 fs Protonated Parent Rise 676 fs54 fs Parent Slow Rise 26 ps3 ps Protonated Parent Decay 22 ps4.2 ps Dimer Fast Decay 800 fs109 fs Slow Dimer Decay 25 ps3 ps Ar Data 10

Model 11  Monomer:  Dimer: 3p 3s Pump Probe P+P+ P+P+ P + F + ~670 fs 67 ps P (3s) P (3p) 3p 3s Pump Probe D+D+ D+D+ D + PH + ~670 fs P+P+ P+P+ ~25 ps D (3s) P (3s) D (3p) Long Lived State

Proton Transfer H. Transfer 12 Dimer iPr Me N N C C H H H H H H iPr Me N N C C H H H H H H Protonated Parent Mass – 86 (Neutral) Protonated Parent Mass – 86 (Neutral) Protonated Parent

Is it a Proton Transfer or Hydrogen Transfer? 13 Proton Transfer ! 2.86 Å 2.91 Å 1.87 Å hν DFT (B3LYP) g* ΔE = eV ΔE = eV

Ionization makes the dimer stronger Strong H-bonding in dimer in the ion state –N……H distance ≈ 1.87 Å (From calculations) –Strength ≈ eV We observe the ultrafast proton transfer in presence of clusters –Estimated time : 40 ps to 1 ns The proton transfer is occurring on Ion surface After the proton transfer the dimer dissociates Ionization makes the dimer stronger Strong H-bonding in dimer in the ion state –N……H distance ≈ 1.87 Å (From calculations) –Strength ≈ eV We observe the ultrafast proton transfer in presence of clusters –Estimated time : 40 ps to 1 ns The proton transfer is occurring on Ion surface After the proton transfer the dimer dissociates 14 Conclusion

Acknowledgements Prof. Peter M. Weber Dr. Michael P. Minitti Dr. Joseph Geiser Dr. Fedor Rudakov Joe Bush Jie Bao Bryan Bayes Mike Levy Xiao Liang Christine Buehler Prof. Peter M. Weber Dr. Michael P. Minitti Dr. Joseph Geiser Dr. Fedor Rudakov Joe Bush Jie Bao Bryan Bayes Mike Levy Xiao Liang Christine Buehler 15 $$$ DOE – Basic Sciences $$$ DOE – Basic Sciences