Sanghamitra Deb, Michael P. Minitti, Peter M. Weber Department Of Chemistry Brown University 64 th...
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Transcript of Sanghamitra Deb, Michael P. Minitti, Peter M. Weber Department Of Chemistry Brown University 64 th...
Sanghamitra Deb, Michael P. Minitti, Peter M.
WeberDepartment Of Chemistry
Brown University64th OSU International
Symposium on Molecular Spectroscopy
hv
June 26th 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 StatesRydberg States
EB RRyd(n )2
€
En =RRydn2
δ – quantum defect accounts for the shielding created by the molecular ion core
2Kuthirummal, N.; Weber, P. M., J. Mol. Struc. 2006, 787, 163
RRyd = 13.6 eV – Rydberg Constantn – 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
3
GoalGoal
4
3s
3p
Ion
X
e-
e-
418 nm
EB(3p)
EB(3s)
Gosselin, J. L.; Minitti, M. P.; Rudakov, F. M.; Sølling, T. I.; Weber, P. M. J. Phys. Chem. A, 2006, 110, 4251.
DMIPA DMIPA (N,N-dimethylisopropylamine)(N,N-dimethylisopropylamine)
Ti:Sapphire Regenerative Amplifier Laser System
ExperimentExperimentBBO
Crystals
Ion MCP
e- MCP
Delay Stage
5
5 kHz Rep. Rate209 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.
3s3s3p3p
3s3s
3p3p ClusterCluster
DMIPA PESDMIPA PES
6
• 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
Fragment
ParentParent
Fragment
Fragment
ParentParent
DimerDimer
TrimerTrimer Higher Order Clusters
Higher Order Clusters
Clusters
Parent and Fragment
DMIPA Mass SpecDMIPA Mass Spec
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Time Resolved Parent Time Resolved Parent PeakPeak
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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 = 88Mass = 88
Parent (Mass=87)Parent (Mass=87)
Model – He DataModel – He Data
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Monomer:Monomer:
3p3p
3s3s
P+ P+ F+
P(3s)P(3s)
P(3p)P(3p)
Time Constants
3σ
Parent Decay 650 fs 12 fs
Fragment Rise 650 fs 12 fs
Fragment Decay 67 ps 3 ps
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Dimer:Dimer:
3p3p
3s3s
D+ D+ PH+ P+
D(3s)D(3s) P(3s)P(3s)
D(3p)D(3p)
Model – Ar DataModel – Ar Data
Parent DecayParent Decay
Parent RiseParent Rise
Higher Isotope of Parent ~ 5.6%
Higher Isotope of Parent ~ 5.6%
Protonated Parent DecayProtonated Parent Decay
Time Constants
3σ
Parent Decay 670 fs 12 fs
Protonated Parent Rise
676 fs 54 fs
Parent Slow Rise
26 ps 3 ps
Protonated Parent Decay
22 ps 4.2 ps
Dimer Fast Decay
800 fs 109 fs
Slow Dimer Decay
25 ps 3 ps
Ar Data Ar Data
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ModelModel
12
Monomer:Monomer: Dimer:Dimer:
3p3p
3s3s
P+ P+ F+
~670 fs~670 fs
P(3s)P(3s)
P(3p)P(3p)
3p3p
3s3s
D+ D+ PH+
~670 fs~670 fs
P+
~25 ps~25 ps
D(3s)D(3s) P(3s)P(3s)
D(3p)D(3p)
Long Lived State
Long Lived State
Proton TransferProton
TransferH. Transfer
H. Transfer
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Dimer
Dimer
iPriPr
MeMe
NN
CC
HH
HHHH
iPriPr
MeMe
NN
CC
HH
HHHH
Protonated Parent
Protonated Parent
Mass – 86 (Neutral)Mass – 86 (Neutral)
Protonated Parent
Protonated Parent
Mass – 86 (Neutral)Mass – 86 (Neutral)
Protonated Parent
Protonated Parent
Is it a Proton Transfer or Hydrogen Is it a Proton Transfer or Hydrogen Transfer?Transfer?
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ProtonProton Transfer !Transfer !
ProtonProton Transfer !Transfer !
2.86 Å
2.91 Å
1.87 Å
hν
DFT (B3LYP) 6-311++g*
ΔE = -0.025 eVΔE = -0.025 eV ΔE = -0.465 eVΔE = -0.465 eV
• Ionization makes the dimer stronger• Strong H-bonding in dimer in the ion
state– N……H distance ≈ 1.87 Å (From
calculations)– Strength ≈ 0.465 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 ≈ 0.465 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
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ConclusionConclusion
AcknowledgementsAcknowledgements
• 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
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$$$DOE – Basic Sciences
$$$DOE – Basic Sciences