electronic spectroscopy of 1-methylpyrene cation and related species. d. kokkin, c. marshall, a....
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Electronic Spectroscopy of1-Methylpyrene cation
and related species.
D. Kokkin, C. Marshall, A. Bonnamy, And C. Joblin
and
A. Simon
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The Unidentified Infra Red (UIR) bands
Infrared emission features that match the vibrational modes of the polycyclic aromatic hydrocarbons (PAHs)
Must survive UV radiation field conditions
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The Diffuse Interstellar Bands
Series of absorption bands between 400 nm and about 1400 nm
Observed in both galactic and extra-galactic sources
Primarily in diffuse sources but weakly observed in dense clouds
http://bjm.scs.uiuc.edu/research/opb2.php
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Properties of the DIBs
UV flux seems important:Too little or too much UV
removes the DIB absorbersIRC+10216 vs IRAS06530-0213
Chemical composition of local environment important
Some DIBs show structure:Isotopic?Rotational?
Sarre, MNRAS 277, 1995
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Why 1-Methylpyrene cation?
Léger, A., D’Hendecourt, L., & Défourneau, D. (1995), A&A, 293, L53
1- Methylene pyrene or related photo product possible carrier for indicated DIBs from matrix spectra.
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The Experiment – FTICR-MSThe PIRENEA-Setup
Cold ICR cell
Technique validated in the work of Useli Bacchitta et al in obtaining the optical spectra of isolated PAH cations by resonant multi-photon dissociation
Useli Bacchitta et al. 2010 chem Phys, 371,16
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The PIRENEA set-up for astrochemistry
UV-Visible irradiation
Superconductor magnet (5T)
ICR cell
Turbo-molecular pump
OPO laser210 nm – 2 µm
Solid pellet
Ablation laser (266 nm)
Externalcold shield
Internal cold shield
zr
P ~ 10-11 mbarT=35 K
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8
Absorption of UV photon - Relaxation mechanims
D0
D1
Dn
hinterstellar
Energy
Q1?
PAH+
IC ICIVRIVR
Dissociation ?H, C2H2
(H2)
IR Emission AIBs
IV. NRT, PAH et MIS
~10-12 s
10-2 - 1 s
From short timescales (~ps) to very long timescales (~s)
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Ion trap + MPD techniqueAdvantage:
production in situ of isolated cations in various hydrogenation state provide good band position for the gas-phase ion oscillator strength derived by modelling
Disadvantage:
no access to the profile of the cold ion
vibronic structure due to :- the multiphotonic absorption process- the preparation of the ions (ejection process in particular)
GASPARIM ANR project:
improve the cooling of the ions (collaboration with S. Schlemmer- Univ. Cologne)
implement a two colour laser scheme (collaboration with T. Pino & Ph. Bréchignac at ISMO-Univ. Paris Sud)
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The Results – 1-Methylpyrene cation
189 ?
215 ?
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The Results – 1-Methylpyrene cation
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Theory
• Gaussian 09– B3LYP functionals for geometry optimization and
frequency calculations.– BLYP functionals for vertical excited state calculations.
– 6-31G(d,p) basis set was chosen after comparing computational cost and accuracy on pyrene cation.
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Breakdown Pathway
-H
http://www.chem.uic.edu
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Spectroscopy of 1-Methylpyrene cation
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Spectroscopy of 1-Methylpyrene cation
420 430 440 450 460 470 480 4900
5
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35
40
45
Wavelength (nm)
Perc
ent D
issoc
iatio
n
D5
Improved cooling
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Spectroscopy of 1-Methylpyrene cation
Tan, X., Salama, F. (2006), Chem. Phys. Letters., 422, 518-521
420 430 440 450 460 470 480 4900
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Wavelength (nm)
Perc
ent D
issoc
iatio
n
D5
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Spectroscopy of 1-Methylpyrene cation
TransitionEnergy of transition
Wavelength (nm) (TD-DFT) (Experiment)
Oscillator strength
D4 ← D0
2.4902 eV 20084.8 (497.89) -
0.0185
D5 ← D0
2.8807 eV 23234.2 (430.40)
22520(444)(441 CRD)
0.2339
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The Results – CH2 - C16H9+ cation
410 430 450 470 490 510 5300
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Wavelength (nm)
Perc
ent D
issoc
iatio
n
S3
S2
2 possible structures. The seven member ring system has a calculated S1 state at 455.11 f=0.1149
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Breakdown Pathway
-H
http://www.chem.uic.edu
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The Results – CH2 - C16H9+ cation
410 430 450 470 490 510 5300
5
10
15
20
25
30
35
Wavelength (nm)
Perc
ent D
issoc
iatio
n
S3
S2
2 possible structures. The seven member ring system has a calculated S1 state at 455.11 f=0.1149
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The Results – CH2 - C16H9+ cation
TransitionEnergy of transition
Wavelength (nm) (TD-DFT) (Experiment)
Oscillator strength
S1 ← S0 2.2230 eV17929.9 (577.73)
- f=0.0608
S2 ← S0 2.5120 eV20260.6 (493.57)
19685 (508 nm)
f=0.1241
S3 ← S0 2.9193 eV23545.5 (424.71)
?? f =0.1520
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m/z=189
• Calculated electronic properties. Singlet ground state.
• 5 member ring IR spectrum to confirm. Ring mode at calculated 1713cm-1(~1670cm-1), which is not present in system with just 6 member rings.
548nm 0.0125
406nm 0.1152
317nm 0.0818
255nm 0.31
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The Future
• 2 laser experiment. Preliminary experiments underway. OPO to probe the spectroscopy with the second laser to break.
• 2 laser ablation scheme for better control of the ablation – ionization process
425 430 435 440 445 450 4550.600000000000001
0.650000000000001
0.700000000000001
0.750000000000001
0.800000000000001
0.850000000000001
0.900000000000001
0.950000000000001
1
Wavelength (nm)
Pare
nt S
igna
l
~30% Dissociation
OPO
+
355nm
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The Future
215.1
214.1
213.1
185.1
187.1
189.1
190.1
161.1
159.1
135.0
134.0
111.0
110.0
109.0
87.086.0
85.0
63.0
62.0
61.0
39.0
C3H3+
C5H3+
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Acknowledgements• Loic Nogues
• $$$$$: French Nationale de la Recherche (ANR), under grant “Gas-phase PAH research for the interstellar medium.” (GASPARIM)
• CNRS / Programme National Physique et Chimie du Milieu Interstellaire
• University Paul Sabatier and Observatory Midi-Pyrénées (AST Molecules and Grains: from laboratory to the universe)
• Super-Computing Center of Midi-Pyrenees (http://www.calmip.cict.fr)