Polycyclic Aromatic Hydrocarbons and Astrophysics

404 Pages·1986·15.52 MB·English

by  L. d’Hendecourt (auth.)

Polycyclic Aromatic Hydrocarbons and Astrophysics
NATO ASI Series
Advanced Science Institutes Series
A series presentmg the results of activities sponsored by the NATO Science Committee,
which aims at the dissemination of advanced scientific and technological knowledge,
with a view to strengthening links between scientific communities.
The series is published by an international board of publishers in conjunction with the
NATO Scientific Affairs Division
A Life Sciences Plenum Publishing Corporation
B Physics London and New York
C Mathematical D. Reidel Publishing Company
and Physical Sciences Dordrecht, Boston, Lancaster and Tokyo
D Behavioural and Social Sciences Martinus Nijhoff Publishers
E Engineering and The Hague, Boston and Lancaster
Materials Sciences
F Computer and Systems Sciences Springer-Verlag
G Ecological Sciences Berlin, Heidelberg, New York and Tokyo
Series C: Mathematical and Physical Sciences Vol. 191
Polycyclic Aromatic Hydrocarbons
and Astrophysics
edited by
A. Leger
and
L. d'Hendecourt
Groupe de Physique des Solides de l'Ecole Normale Superieure,
Universite Paris VII, France
and
N. Boccara
C. E. N., Saclay, France
D. Reidel Publishing Company
Dordrecht / Boston / Lancaster / Tokyo
Published in cooperation with NATO Scientific Affairs Division
Proceedings of the NATO Advanced Research and CNRS Workshop on
Polycyclic Aromatic Hydrocarbons and Astrophysics
Les Houches, France
February 17-22, 1986
Library of Congress CataloginQ in Publication Data
Polycyclic aromatic hydrocarbons and astrophysics.
(NATO ASI series. Series C, Mathematical and physical sciences; v. 191)
"Published in cooperation with NATO Scientific Affairs Division."
"Proceedings of the NATO Advanced Research and CNRS Workshop on Polycyclic
Aromatic Hydrocarbons and Astrophysics, Les Houches, France, February 17 - 22,
1986"-Verso t.p.
Includes index.
1. Interstellar matter-Congresses. 2. Polycyclic aromatic
hydrocarbons-Congresses. I. Leger, A. (Alain), 1943- . II. Hendecourt, L. (Louis)
d',1953- . III. Boccara, N. (Nino) IV. NATO Advanced Research and CNRS
Workshop on Polycyclic Aromatic Hydrocarbons and Astrophysics (1986: Les Houches,
Haute-Savoie, France) V. Series: NATO ASI series.
Series C, Mathematical and physical sciences; vol. 191.
QB790.P65 1986 523.1.'12 86-22022
ISBN-13: 978-94-010-8619-6 e-ISBN-13: 978-94-009-4776-4
001: 10. 1007/978-94-009-4776-4
Published by D. Reidel Publishing Company
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© 1987 by D. Reidel Publishing Company, Dordrecht, Holland.
Softcover reprint of the hardcover 1s t edition 1987
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L E S HOUCHES
CENTRE DE PHYSIQUE
operated by the
Universit~ Scientifique et M~dicale de Grenoble
Counc:il Hembers : M. Tanche, president, D. Bloch, vice-president,
P. Averbuch, R. Balian, N. Boccara, R. Carr~, C. DeWitt, J.P. Hansen,
S. Haroche, J.C. Lacoume, R. Maynard, A. Neveu, P. Papon, Y. Rocard,
R. Romestain, R. Stora, D. Thoulouze, N. Vinh Mau, G. Weill.
D:irect:or Nino Boccara, CEN-Saclay
POLYCYCLIC AROMATIC HYDROCARBONS AND ASTROPHYSICS
February 17 - 22, 1986
Sess:ion Organ:izat::ion CommJ.'t:t:ee. : A. Leger, L. d'Hendecourt, A. Beswick,
J. Friedel, S. Leach, A. Omont, N. Panagia, J.L. Puget, W. SchmidL
TABLE OF CONTENTS
Preface xi
Organizing Committee and List of Participants xiii
Section 1 : INTRODUCTION
Objectives of the Workshop I
by L. d'Hendecourt
Photons, Molecules and Solids in Interstellar and Circum-
stellar Regions: an Introduction for Non-Astronomers 3
by M. Jura
Section 2 : PHYSICS AND CHEMISTRY OF GRAPHITE, CARBONACEOUS
GRAINS AND CLUSTERS
On the Electronic Structure of Graphite 15
by P. Joyes
Various Kinds of Solid Carbon: Structure and Optical
Properties 31
by A. Marchand
Gas/Carbonaceous Surface Interactions 55
by A. Thorny, P. Wehrer
VUV to FIR Laboratory Observations on Submicron Amorphous
Carbon Particles 63
by E. Bussoletti, L. Colangeli, A. Borghesi
Spectroscopy of Matrix-Isolated Carbon Molecules in the
UV, VIS, and IR Spectral Range 75
by W. Kratschmer, K. Nachtigall
Remarkable Periodicities in the Mass Spectra of Carbon
Aggregates 85
by P. Joyes
Reactions of Thermal Hydrogen Atoms and Energetic
Hydrogen and Oxygen Ions with Pyrolytic Graphite 95
by V. Philipps, E. Vietzke
viii TABLE OF CONTENTS
Section 3 : PHYSICS AND CHEMISTRY OF POLYCYCLIC AROMATIC
HYDROCARBONS (PAD's)
Photophysics, Electronic Spectroscopy and Relaxation
of Molecular Ions and Radicals with Special Reference to
Polycyclic Aromatic Hydrocarbone 99
by S. Leach
Fluorescence Lineshapes of Polyatomic Molecules - Spectro-
scopy without Eigenstates 129
by S. Mukamel, K. Shan, Yi Jing Yan
Structure and Chemistry of PAH's 149
by W. Schmidt
Synthesis and Spectroscopy of Tribenzo(a,g,m)Coronene,
a New, Exceptionally Stable, Fully Benzenoid PAH 165
by S. Obenland, W. Schmidt
Hot Carbon Atoms as a Potential Source for Polycyclic
Aromatic Hydrocarbons 173
by K. Rossler
Section 4 : CARBONACEOUS MATERIALS AND ASTROPHYSICS
Carbon Components of Interstellar Dust 177
by J.M. Greenberg, M.S. De Groot, G.P. Van der Zwet
Molecular Origin of the 216 nm Interstellar Hump 183
by G.P. Van der Zwet, M.S. De Groot, F. Baas,
J.M. Greenberg
Chains and Grains in Interstellar Space 197
by H.W. Kroto
Mid Infrared Excess and Ultraviolet Extinction 207
by P. Cox, A. Leene
High Spectral Resolution Observation of the 3.3 pm
Emission Band and Comparison with Laboratory-Synthesized
Quenched Carbonaceous Composite (QCC) 213
by T. Onaka, A. Sakata, S. Wada Y. Nakada,
A.T. Tokunaga, K. Sellgren, R.G. Smith, D.L. DePoy
DISCUSSION I : Carbon in the Interstellar Medium 215
Chairman: P.G. Martin
TABLE OF CONTENTS ix
Section 5 : POLYCYCLIC AROMATIC HYDROCARBONS AND ASTROPHYSICS
Identification of PAH's in Astronomical IR Spectra
- Implications 223
by A. Leger, L. d'Hendecourt
The IR Emission Features : Emission from PAH Molecules
and Amorphous Carbon Particles 255
by L.J. Allamandola, A.G.G.M. Tielens, J.R. Barker
The Hydrogen Coverage of Interstellar PAH's 273
by A.G.G.M. Tielens, L.J. Allamandola, J.R. Barker,
M. Cohen
New Observations of Infrared Astronomical Bands: lRAS-LRS
and 3 ~m Ground-Based Spectra 287
by M. de Muizon, L.B. d'Hendecourt, T.R. Geballe
Distribution of PAH in the Galaxy Derived from the IRAS
Data 303
by J.L. Puget
Infrared Features in Extragalactic Objects 307
by P.F. Roche
Very Small Grains in Spiral Galaxies 317
by S.K. Ghosh, S. Drapatz
lRAS Observations of a "Typical" Dark Cloud 323
by R.J. Laureijs, G. Chlewicki, F.O. Clark
Coal Tar as a Laboratory Analog of an Interstellar PAH
Mixture 327
by T.J. Wdowiak
Hydrogenated Amorphous Carbon (a:C-H) in the Planetary
Nebula NGC 7027 329
by J.H. Goebel
Visual and Infrared Fluorescence from L1780 335
by G. Chlewicki, R.J. Laureijs
DISCUSSION II : Interpretation of IR Observations 339
ChaIrman : L. Allamandola
Section 6 : DIFFUSE INTERSTELLAR BANDS
Possible Carriers of the Diffuse Interstellar Bands 351
by G. Van der Zwet
DISCUSSION III : The Diffuse Interstellar Bands. Are they
Carried by PAH's ? 367
Chairman : M. Jura
x TABLE OF CONTENTS
Section 7 PHYSICS AND CHEMISTRY OF PAD t S IN THE INTERSTELLAR
MEDIUM
Physic.s and Chemistry of Interstellar Polyc.yc.lic. Aromatic.
Molec.ules 371
by A. Omont
Formation, Destruc.tion and Exc.itation of Carbon Grains
and PAR Molec.ules 373
by W.W. Duley
Polyaromatic. Hydroc.arbons and the Condensation of
Carbon in Stellar Winds 387
by R. Keller
Subject Index 399
PREFACE
The near Infra-Red emission of the Interstellar Medium is a very
puzzling subject. In the brightest regions, where spectroscopic observa
tions are possible from the ground, several bands (3.3 - 3.4 - 6.2 -
7.7 - 8.6 - 11.3 ~m) have been observed since 1973. The absence of
satisfying explanation was so obvious that they were called "Unidenti
fied IR Emission Bands".
The puzzle still increased when were known the first results of the
general IR sky survey made by the satellite IRAS. On a large scale, the
near IR emission of the Interstellar medium was expected to be very
small but it was observed to be about one third of the total IR emission
for our own galaxy ..•
The situation has moved in 1984 when it was suggested that a class of
stable organic molecules, the Polycyclic Aromatic Hydrocarbons (PAH's)
could be at the origin of this near IR emission. Initially based on the
required refractory character of particules that should be heated to
high temperature without subliming, this hypothesis leads to a sugges
tive spectroscopic similarity with the observed astronomical bands.
This hypothesis is attractive and it has many implications, for ins
tance, the PAHs would be the most abundant organic molecules in the
universe. However, many points have to be clarified and the different
consequences of this suggestion should be explored.
To reach such a goal, advanced enlightening from Chemistry, Solid State
and Molecular Physics are needed. On the other hand, the astrophysical
conditions provide a unique situation for fundamental studies in these
disciplines: highly isolated molecules, species unstable under labora
tory conditions (radicals), long time scales ...
Such conditions motivated the organization of this LnterdLscLplLnary
meetLng between chemists, solid state and molecular physicists and
astrophysicists. All the participants have tried to play the game of
interdisciplinary exchanges, paying special attention to be accessible
to scientists not in their own field and not using technical concepts or
vocabulary without prior introduction.
This was not always easy, for instance, we had discussions to decide
whether'distinct appellations in two disciplines were describing the
same physical phenomenum or not. The net result of this effort was quite
positive and stimulating by all accounts.
xi