The Spectroscopy of Flames PDF
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THE SPECTROSCOPY OF FLAMES The Spectroscopy of Flames A.G.GAYDON D.Se., F.R.S. Warren Research Fellow of the Royal Society and Emeritus Professor of Molecular Spectroscopy Imperial College, London SECOND EDITION LONDON CHAPMAN AND HALL First published 1957 by Chapman and Hall Ltd 11 New Fetter Lane, London EC4 P 4EE Second edition 1974 © 1957, 1974 A. G. Gaydon Softcover reprint ofthe hardcover 1st edition 1957 Typeset by Preface Ltd, Salisbury, Wilts and printed in Great Britain by T & A Constable Ltd, Edinburgh ISBN-13: 978-94-009-5722-0 e-ISBN- 13: 978-94-009-5720-6 DOl: 10.1007/978-94-009-5720-6 All rights reserved. No part of this book may be reprinted, or reproduced or utilized in any form or by any electronic, mechanical or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the Publisher. Distributed in the U.S.A. by Halsted Press, a Division of John Wiley & Sons, Inc., New York Preface to Second Edition The spectrum of a candle flame was first mapped by Swan in 1857 and early observations on spectra of metals in flames were made by Bunsen and Kirchhoff around 1860. Since then investigations have continued at an increasing pace and knowledge obtained from these spectroscopic studies is accepted as making an important contribu tion to the understanding of flame processes. I have myself been working in this field for some 40 years now and have been associated with some of the recent advances in techniques. My small monograph on Spectroscopy and Combustion Theory first appeared in 1942, and the revised edition in 1948. This summarized not only direct observations on the visible and ultra violet emission spectra of flames, but also covered the infra-red region and absorption spectroscopy. Indirect applications, such as the use of spectroscopic data for determining dissociation equilibria and flame temperatures were also included. The spectroscopic observations were interpreted in relation to chemical processes of combustion, to the initial energy distribution resulting from the reactions, and to the state of equilibrium in the flame gases. This earlier monograph served to summarize work up to about 1947 and, I hope, to stimulate further research. These research developments, and also the coverage of parts of the field in my other books, Flames, their Structure, Radiation and Temperature, jointly with H. G. Wolfhard, and my Dissociation Energies, led to a complete revision of the older monograph under the new title Spectroscopy of Flames in 1957. That edition covered many exciting new developments - the work on low-pressure flames, burners for flat diffusion and flat premixed flames, flames supported by free atoms, flash photolysis, early investigations in shock tubes, and the use of isotope tracer methods. The 1957 edition did indeed stand the test of time rather better than the older monograph, because the information about flame spectra and flame processes was by then much more definite. vi PREFACE TO SECOND EDITION During the 17 years since the previous edition was prepared there have been many refinements in techniques and some important related advances, such as the discovery of the laser and the use of atomic absorption and atomic fluorescence for analytical work. For this thorough revision the whole book has been completely re worked, but the same plan has been retained so that it appears, deceptively, similar to the previous edition. It is hoped that the new book is now in a sufficiently definitive form to be of continuing value, because although further advances are to be expected and hoped for, the main facts, such as the identity of emitting and absorbing species and the reactions forming them in flames, are now established. Many of the older publications tend to get forgotten, but my long continuity of work in this field has enabled me to make use of old data where still relevant. The book deals primarily with the use of spectroscopic observa tions to interpret combustion processes in flames and flame structure, including explosion flames and engines. This is not a book on flame photometry, but the understanding of flame equilibria, and departures therefrom, is relevant to this subject and in the final chapter I have commented on the use of flames for spectrochemical analysis including the recently developed atomic absorption and atomic fluorescence methods. I have endeavoured to present the ,subject in such a way that the book may be of service to those engaged in research, but so that it may be read easily by the beginner and the non-specialist. The treatment is not mathematical, and where an understanding of the theory of molecular spectra is necessary I have endeavoured to give this theory in simple terms. I have included a fairly extensive Bibliography and an Appendix, giving tables of wavelengths, and in this edition wavenumbers as well, of all the main band spectra frequently found in flames and combustion systems; these should make the book valuable for reference purposes. My early work owes much to the initial stimulation of the late Professors Alfred Fowler and Sir Alfred Egerton, and also I have benefited from collaboration, at Imperial College, with my former colleagues Drs H. P. Broida, R. A. Durie, P. F. Jessen, N. P. W. Moore, W. M. Vaidya and H. G. Wolfhard, to whom I express my PREFACE TO SECOND EDITION vii thanks. I am grateful to my wife and Miss D. Waller for some help with indexing and proof reading. I would also like to acknowledge support over many years from the Warren Research Fund of the Royal Society. Department of Chemical Engineering and Chemical Technology, A.G.G. Imperial College, London, S. W. 7. April 1974. ix Contents Preface page v I. FLAME SPECTRA 1 The purpose of studying flame spectra - Types of spectra - The structure of flames - The spectrum of the Bunsen flame - Equilibria, radiation and collision processes. II. EXPERIMENTAL METHODS 14 The recording of spectra - Spectrographic equipment - Optical systems - The study of absorption spectra - Wavelength determination - Intensity measurements - Effects of flame shape. III. SPECIAL TECHNIQUES 41 Flat flames - Low-pressure flames - Temperature effects on flames - Atomic flames - Flash photolysis - Shock tube studies - Fluorescence and laser-Raman scattering - Use of isotope shifts IV. INTRODUCTION TO THE THEORY OF SPECTRA 65 Line or atomic spectra - Bohr theory - The spectra of diatomic molecules: vibrational structure - Rotational structure of the spectra of diatomic molecules - Electronic states of diatomic molecules - Vibrational intensity distribution: the Franck-Condon principle - Predissociation - Infra-red spectra - Raman spectra - Electronic spectra of polyatomic molecules - Con tinuous spectra - Ionization continua - Dissociation continua - Association continua - The width and shape of spectrum lines x CONTENTS V. HYDROGEN FLAMES 99 The OH bands - Hydrogen/air flames - Hydrogen! oxygen flames - Pressure effects - Absorption spectra - Excitation of metal spectra in H /0 /N flames - 2 2 2 Candoluminescence - Applications to combustion mechanism - The hydrogen/nitrous oxide flame - Flames with NO and N0 2 VI. THE CARBON MONOXIDE FLAME 127 The spectrum - The carbon monoxide flame bands - The excitation of the flame bands - The continuous spectrum: pressure and temperature effects - Com bustion processes for carbon monoxide - Flames of carbon and carbon suboxide VII. THE SPECTRA OF ORGANIC FLAMES 144 The CH bands - Bands of C Vaidya's hydrocarbon 2 - flame bands (HCO) - The 4050 A "comet head" group (C EmelaIs's cool flame bands (CH 0) - Band 3) - 2 systems of CO - Other band systems in flames - The carbon line, X2478 - Premixed flames - Diffusion flames - Cool flames and preignition glows - Absorp- tion spectra VIII. MEASUREMENTS OF EFFECTIVE TEMPERATURE 182 AND STUDIES WITH SPECIAL SOURCES Electronic excitation temperatures - Translational temperatures from Doppler broadening - Measurement of rotational temperatures: OH - Rotational tempera tures for CH, C NH etc. - Effective vibrational 2, temperatures - Predissociation - Flash photolysis - Atomic flames - Spectra excited by shock waves - Occurrence of C and CH in some special flames - 2 Isotope tracer experiments IX. THE INFRA-RED REGION 221 The amount of radiation from flames - Infra-red spectra of organic flames - Relative band intensities and temperature measurements - Radiation from explosion flames - Cool flames - Flames with nitrous oxide - Flames with halogens CONTENTS xi X. FLAME STRUCTURE AND REACTION PROCESSES 244 Reactions in cool flames - The formaldehyde excitation process - Reactions in diffusion flames - Reactions in premixed flames - Carbon formation in premixed flames - Concentrations of free radicals - Reactions forming excited species - Ionization and electron temperatures - The high electronic excitation in the flame front - Effects on flame structure of lags in equipartition of energy. XI. EXPLOSIONS, ENGINES AND INDUSTRIAL FLAMES 282 Explosions in closed vessels - Detonations - The internal combustion engine: flame fronts and afterburn- ing - Knock - Compression-ignition (diesel) engines - Engines with continuous combustion - Exhaust flames - Furnace flames - Solid propellants. XII. FLAMES CONTAINING NITROGEN, HALOGENS, 296 SULPHUR AND INORGANIC SUBSTANCES Flames of ammonia, hydrazine etc. - Flames of organic nitrogen compounds - Flames supported by oxides of nitrogen - Formation of oxides of J.litrogen - Ozone Halogens in oxidizing flames - Flames supported by halogens - Flames of sulphur, hydrogen sulphide and carbon disulphide - Flames with added SO SO or 2, 3 H S - Phosphorus in flames - Flames containing boron 2 - Metals in flames. XIII. FLAME SPECTROPHOTOMETRY 320 The choice of flame type - The burner and spray system - Recording methods - The relation between line intensity and concentration - Interference by one element with the estimation of another - Atomic absorption - Atomic fluorescence - Effects of flame disequilibria APPENDIX I Band spectra emitted by flames 338 II Absorption spectra 369 III Some atomic and molecular energy levels and constants 376 xli CONTENTS REFERENCES 381 AUTHOR INDEX 397 SUBJECT INDEX (Including symbols used and values of physical constants) 405 PLA TES Plates 1 to 8 appear between pages 212-213
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