Electronic Spectroscopy of 1-Methylpyrene cation and related species. D. Kokkin, C. Marshall, A....
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Transcript of Electronic Spectroscopy of 1-Methylpyrene cation and related species. D. Kokkin, C. Marshall, A....
Electronic Spectroscopy of1-Methylpyrene cation
and related species.
D. Kokkin, C. Marshall, A. Bonnamy, And C. Joblin
and
A. Simon
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
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
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
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.
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
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
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)
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)
The Results – 1-Methylpyrene cation
189 ?
215 ?
The Results – 1-Methylpyrene cation
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.
Breakdown Pathway
-H
http://www.chem.uic.edu
Spectroscopy of 1-Methylpyrene cation
Spectroscopy of 1-Methylpyrene cation
420 430 440 450 460 470 480 4900
5
10
15
20
25
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35
40
45
Wavelength (nm)
Perc
ent D
issoc
iatio
n
D5
Improved cooling
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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40
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Wavelength (nm)
Perc
ent D
issoc
iatio
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D5
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
The Results – CH2 - C16H9+ cation
410 430 450 470 490 510 5300
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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
Breakdown Pathway
-H
http://www.chem.uic.edu
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
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
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
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
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+
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)