Astrophysics of the Diffuse Universe
The book is designed as an astrophysics textbook to provide a comprehensive introduction to the physics of Interstellar Matter. It is aimed primarily at those undertaking postgraduate courses, or those doing advanced projects as part of honours undergradu
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ASTRO TOMY Ai D \STRC)PlfYSICS LIBRARY I. Appenzeller, Heidelberg, Germany G. Bomer, Garching, Gennany A. Burkert, Miinchen, Gennany M. A. Dopita, Canberra, Australia A. Eckart, Koln, Germany T. Encrenaz, Meudon, France M. Harwit, Washington, DC, USA R. Kippenhahn, Gottingen, Germany J. Lequeux, Paris, France A. Maeder, Sauvemy, Switzerland V. Trimble, College Park, MD, and Irvine, CA, USA
M.A. Dopita R. S. Sutherland
Astrophysics of the Diffuse Universe With 70 Figures
~ Springer
Professor Michael A. Dopita Dr. Ralph S. Sutherland The Australian National University Research School of Astronomy and Astrophysics Weston Creek Post Office Canberra, ACT 2611, Australia
Cover picture: The central regions of the Lagoon Nebula in the light ofHa and forbidden [0 III]'\ 5007 \lA. The false colours are chosen to emphasise the differences in ionization conditions within the nebula as the ratio of the emission lines change. Young hot stars are photoionizing the nebula in a Huorescent process which converts UV radiation into visible light, mostly as emission lines of hydrogen and other light elements. Dark dust lanes and globules show where dense cores of interstellar clouds are still condensing, and where new star formation may still be taking place. (Credit: Sutherland, R.S. & Bessell, M. 1999, ANU Research School of Astronomy and Astrophysics, Mt Stromlo Observatory. )
Library of Congress Cataloging-in-Publication Data. Dopita, Michael A. Astrophysics of the diffuse universelM. A. Dopita, R. S. Sutherland. p.cm. - (Astronomy and astrophysics library, [SSN 0941-7834) Includes bibliographical references and index.
1. Interstellar matter. 2. Astrophysics. I. Sutherland, R.S. (Ralph S.), 1964-. II. Title. III. Series QB790.D67 2003 523.1' 135-~
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Separation (A) Fig. 2.6. The Morse potential for H 2 . The actual potential inferred from detailed spectroscopy is the solid curve, the Morse potential is given by the dashed curve.
This gives quantized vibrational states at the following energies: Cv
=
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We -
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where We is the vibration frequency as before and Xe is the 'anharmonicity constant'. We can see that W = we [l-x e (v+ 1/2)]' so the frequency difference between levels slowly decreases compared to the harmonic vibration model when Xe is typically small and positive (rv 0.01). The anharmonic oscillator has more relaxed selection rules, so that I1v = ±1, ±2, ±3, .... However, the transition probabilities decrease with larger changes in the vibrational quantum number. As a result, often only the first three or so transitions are observable at we (1 - 2x e ), 2we(1 - 3x e ), and 3we(1- 4xe). For CO, We = 2169.7 cm-I, and Xe = 0.0172.
2.5 Ro-Vibrational Spectra
33
2.5 Ro-Vibrational Spectra Given that the energies associated with the rotational states are of order B, or 10 cm
