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

7

Time Resolved Parent Time Resolved Parent PeakPeak

8

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

9

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

10

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

11

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

13

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?

14

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

15

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

16

$$$DOE – Basic Sciences

$$$DOE – Basic Sciences