TB05montero.ppt
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Femtosecond Timescale Evolution of Pyrrole
Electronic Excitation
R. Montero, A. Peralta Conde , V. Ovejas, F. Castaño, A.
Longarte.
(Universidad del País Vasco UPV/EHU. Spain)
Ohio, June-2012
Introduction
ππ*
πσ*
ππ*
πσ*
ππ*
ππ*
πσ*
ππ*
ππ*
ππ*
ππ*
πσ*
Introduction
•
Spectroscopy
•
Dynamics
217 nm
Lippert et al., ChemPhysChem 5, 1423 (2004).
250 nm
To follow the relaxation dynamics directly on the parent molecule.
(Time resolved non resonant ionization).
Wei et al., Faraday Discuss. 127, 267 (2004).
Cronin et al., Phys. Chem. Chem. Phys. 6, 5031 (2004).
Cronin et al., Phys. Chem. Chem. Phys. 8, 3440 (2006).
Experiment
Energy
•Experiment
•Set up
ππ*
πσ*
•217 nm-230 nm tunability.
GS
N-H
Pump: 265-217 nm
Probe: 800 nm
IRF: 55-80 fs
Results: preliminary view
264 nm
250 nm
Coherent approach based on time
dependent Schrödinger eq. required.
(Optical Bloch equations)
225 nm
217 nm
-Very fast dynamics.
-(Out of resonance
experiments) signal
wider than IRF and
shifted by 5-10 fs.
(incompatible with a
single exponential).
-Fit:
gaussian+ultrafast
decay.
-265 nm is out of
resonance of any
excited state and
show dynamics!!
Coherent Population Return (CPR)
• Description in the adiabatic basis
Adiabatic condition:
N. V. Vitanov et al. Opt. Commun.,199, 117126, 2001.
A. Peralta Conde et al. Phys. Rev. Lett. 97, 243004, 2006.
Influence of CPR effect in the excitation of molecules with ultrashort laser
pulses
S2
S1
Dark state
Δ › 1/τ
S0
Chem. Phys. Chem. 16, 3420, (2010).
Results
The model for pyrrole: Optical Bloch Eq. for a multilevel system
11 0 g (t )12 j 21 j
i
2
22 j 0 g (t )12 j 21 j 22 22
i
2
33 j 22 22 j 33 33 j
12 j
i
22
i 2 j 21 j
0 g (t ) 22 j 11 j
2
2
N
N
j 0
j 0
22 22 j ; 33 33 j
Results
264 nm
252 nm
225 nm
217 nm
τππ*=19±3 fs
τπσ*=15±3 fs
σππ*= 1.3 σπσ*
Results
•Signal vs Δ (adiabatic excitation of ππ)
2 (t )
P 22(t )
42
A. Peralta conde el al.
Eur. Phys. J. D 51, 289–294 (2009)
If (x-A2)=Δ,
A2 Should be the energy of the state
responsible of the adiabatic excitation
Conclusions
•Dynamics observed in the parent ion
•Observation of the πσ* state dynamics to the red
of the lowest electronic transition can only be
understood in terms of out of resonance excitation
of the intense ππ* transition, and subsequent
internal conversion towards the lower πσ* state
during the adiabatic evolution of the ππ*-laser
interaction.
•τ1=15±3 fs lifetime reflects the loss of ionization
cross-section caused by the wavepacket
movement along the repulsive NH coordinate. In
good agreement with the clasical calculation (11
fs).
•f πσ*/f ππ* ~0.0027.
•The study of isolated systems by coherent
sources of increasing time resolution is required to
consider a great portion of the electronic
spectrum, to properly understand the relaxation
mechanisms.
S2
S1
Δ › 1/τ
S0
Dark state
ACKNOWLEDGEMENTS
Spectroscopy group (Bilbao)
Dr. A. Longarte (G.L).
Dr. F. Castaño.
Dr. A. Peralta Conde.
V. Ovejas. (PhD. Student)
M. Fernández. (PhD. Student)
CLPU (Salamanca)
Dr. J. Vázquez.
(Laser Facility)
Supporting information
Methyl Pyrrole
S1 243 nm
S2 216 nm
Supporting information
TD/B3LYP/6-311++G(d,p)