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

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Wavelength (nm)

Perc

ent D

issoc

iatio

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D5

Improved cooling

Spectroscopy of 1-Methylpyrene cation

Tan, X., Salama, F. (2006), Chem. Phys. Letters., 422, 518-521

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Wavelength (nm)

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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

The Results – CH2 - C16H9+ cation

410 430 450 470 490 510 5300

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Wavelength (nm)

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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

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Wavelength (nm)

Perc

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issoc

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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)