Table Of ContentFUNDAMENTALS
OF MOLECULAR
SPECTROSCOPY
WALTER S. STRUVE
Department of Chemistry
Iowa State University
Ames, Iowa
WILEY
A WILEY-INTERSCIENCE PUBLICATION
JOHN WILEY & SONS
New York / Chichester / Brisbane / Toronto / Singapore
Copyright © 1989 by John Wiley & Sons, Inc.
All rights reserved. Published simultaneously in Canada.
Reproduction or translation of any part of this work
beyond that permitted by Section 107 or 108 of the
1976 United States Copyright Act without the permission
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permission or further information should be addressed to
the Permissions Department, John Wiley & Sons, Inc.
Library of Congress Cataloging in Publication Data:
Struve, Walter S.
Fundamentals of molecular spectroscopy.
"A Wiley—Interscience publication."
Bibliography: p.
1. Molecular spectroscopy. (cid:9) I. Title.
QC454.M6S87(cid:9) 1989 (cid:9) 539'.6 (cid:9) 88-5459
ISBN 0-471-85424-7
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
To Helen and my family
PREFACE
This book grew out of lecture notes for a graduate-level molecular spectroscopy
course that I developed at Iowa State University between 1974 and 1987. It is
intended to fill a pressing need for a concise introduction to the spectroscopy of
atoms and molecules. I have tried to stress logical continuity throughout, with a
view to developing readers' confidence in their physical intuition and problem-
solving techniques. A suitable quantum mechanical background is furnished by
the first seven and a half chapters of P. W. Atkins' Molecular Quantum
Mechanics, 2d ed. (Oxford University Press, London, 1983): The Schriidinger
equation for simple systems, angular momentum, the hydrogen atom, stationary
state perturbation theory, and the variational theorem are all presumed in this
book. Group theory is used extensively from Chapter 3 on; it is not developed
here, because many excellent texts are available on this subject. A one-semester
undergraduate course in electromagnetism is helpful but not strictly necessary:
The concepts of vector and scalar potentials are introduced in Chapter 1. Other
requisite material, such as time-dependent perturbation theory and second
quantization, is developed in the text.
Eight or nine of the eleven chapters in this book can be comfortably
accommodated within a one-semester course. The underlying time-dependent
perturbation theory for molecule—radiation interactions is emphasized early,
revealing the hierarchies of multipole and multiphoton transitions that can
occur. Several of the chapters are introduced using illustrative spectra from the
literature. This technique, extensively used by Herzberg in his classic series of
monographs, avoids excessive abstraction before spectroscopic applications are
reached. Diatomic rotations and vibrations are introduced explicitly in the
context of the Born-Oppenheimer principle. Electronic band spectra are
examined with careful attention to electronic structure, angular momentum
VII
Viii (cid:9) PREFACE
coupling, and rotational fine structure. The treatment of polyatomic rotations
hinges on a physically transparent demonstration of the commutation rules for
molecule-fixed and space-fixed angular momenta. From these, all of the energy
levels and selection rules that govern microwave spectroscopy are accessible
without recourse to detailed rotational eigenstates. The chapter on polyatomic
electronic spectra focuses on triatomic molecules and aromatic hydrocarbons—
the former for their environmental and astrophysical interest, and the latter for
their illustrations of vibronic coupling and radiationless relaxation phenomena.
Population inversion criteria, specific laser systems, and the principles of
ultrahigh-resolution lasers and ultrashort pulse generation are outlined in a
chapter on lasers, which have emerged as a ubiquitous tool in spectroscopy
laboratories. Some of the higher order terms in the time-dependent perturbation
expansion are fleshed out for several multiphoton spectroscopies (Raman, two-
photon absorption, second-harmonic generation, and CARS) in the final two
chapters. The reader is guided through the powerful diagrammatic perturbation
techniques in a discussion designed to enable facile determination of transition
probabilities for arbitrary multiphoton processes of the reader's choice.
It is my great pleasure to acknowledge the people who made this book
possible. I am particularly indebted to my teachers, Dudley Herschbach and
Roy Gordon, who communicated to me the inherent beauty and cohesiveness of
molecular quantum mechanics. The original suggestion for writing this book
carne from Cheuk-Yiu Ng. David Hoffman made seminal contributions to the
chapter on polyatomic rotations. I am grateful to numerous anonymous referees
for valuable suggestions for improving the manuscript, though, of course, the
responsibility for errors is still mine. The line drawings were supplied by Linda
Emmerson, and Sandra Bellefeuille, Klaus Ruedenberg, and Gregory Atchity
generated the computer graphics. Finally, I must express deep appreciation to
my wife, Helen, whose moral support was essential to completing this work.
WALTER S. STRUVE
Ames, Iowa
June 1988
CONTENTS
CHAPTER 1 RADIATION-MATTER
INTERACTIONS (cid:9) 1
1.1 Classical Electrostatics of Molecules in
Electric Fields (cid:9) 1
1.2 Quantum Theory of Molecules in Static
Electric Fields (cid:9) 4
1.3 Classical Description of Molecules in
Time-Dependent Fields (cid:9) 11
1.4 Time Dependent Perturbation Theory
of Radiation—Matter Interactions (cid:9) 17
1.5 Selection Rules for One-Photon
Transitions (cid:9) 22
References (cid:9) 28
CHAPTER 2 ATOMIC SPECTROSCOPY (cid:9) 33
2.1 Hydrogenlike Spectra (cid:9) 36
2.2 Spin—Orbit Coupling (cid:9) 43
2.3 Structure of Many-Electron Atoms (cid:9) 51
2.4 Angular Momentum Coupling in
Many-Electron Atoms (cid:9) 58
2.5 Many-Electron Atoms: Selection Rules
and Spectra (cid:9) 62
2.6 The Zeeman Effect (cid:9) 66
References (cid:9) 71
ix
