Collisional Effects on Molecular Spectra (eBook)

Laboratory Experiments and Models, Consequences for Applications

Christian Boulet, Jean-Michel Hartmann, Daniel Robert (Autoren)

eBook Download: PDF

2008 | 1. Auflage
432 Seiten
Elsevier Science (Verlag)
978-0-08-056994-9 (ISBN)

Infos

Gas phase molecular spectroscopy is a powerful tool for obtaining information on the geometry and internal structure of isolated molecules as well as on the interactions that they undergo. It enables the study of fundamental parameters and processes and is also used for the sounding of gas media through optical techniques. It has been facing always renewed challenges, due to the considerable improvement of experimental techniques and the increasing demand for accuracy and scope of remote sensing applications.
In practice, the radiating molecule is usually not isolated but diluted in a mixture at significant total pressure. The collisions among the molecules composing the gas can have a large influence on the spectral shape, affecting all wavelength regions through various mechanisms. These must be taken into account for the correct analysis and prediction of the resulting spectra.
This book reviews our current experimental and theoretical knowledge and the practical consequences of collisional effects on molecular spectral shapes in neutral gases. General expressions are first given. They are formal of difficult use for practical calculations often but enable discussion of the approximations leading to simplified situations. The first case examined is that of isolated transitions, with the usual pressure broadening and shifting but also refined effects due to speed dependence and collision-induced velocity changes. Collisional line-mixing, which invalidates the notion of isolated transitions and has spectral consequences when lines are closely spaced, is then discussed within the impact approximation. Regions where the contributions of many distant lines overlap, such as troughs between transitions and band wings, are considered next. For a description of these far wings the finite duration of collisions and concomitant breakdown of the impact approximation must be taken into account. Finally, for long paths or elevated pressures, the dipole or polarizability induced by intermolecular interactions can make significant contributions. Specific models for the description of these collision induced absorption and light scattering processes are presented.
The above mentioned topics are reviewed and discussed from a threefold point of view: the various models, the available data, and the consequences for applications including heat transfer, remote sensing and optical sounding. The extensive bibliography and discussion of some remaining problems complete the text.
• State-of-the-art on the subject
• A bibliography of nearly 1,000 references
• Tools for practical calculations
• Consequences for other scientific fields
• Numerous illustrative examples
• Fulfilling a need since there is no equivalent monograph on the subject

Jean-Michel HARTMANN: born in 1961, « Directeur de Recherche » for the French CNRS (Centre National de la Recherche Scientifique has been carrying research and advising PhD students in the field of the book for about twenty years. He is the director of the French Molecular Spectroscopy Network and the author of more than 100 publications in international journals.

Inhalt

Front Cover 1
COLLISIONAL EFFECTS ON MOLECULAR SPECTRA: Laboratory Experiments and Models, Consequences for Applications 4
Copyright Page 5
TABLE OF CONTENTS 8
FOREWORD 14
ACKNOWLEDGMENTS 16
CHAPTER I INTRODUCTION 18
CHAPTER II GENERAL EQUATIONS 26
II.1 INTRODUCTION 26
II.2 DIPOLE AUTOCORRELATION FUNCTION 27
II.2.1 General formalism 27
II.2.2 The Hamiltonian of the molecular system 30
II.3 TOWARD "CONVENTIONAL" IMPACT THEORIES 33
II.3.1 General properties of the correlation function 33
II.3.2 The binary collision approximation 34
II.3.3 Initial statistical correlations 36
II.3.4 The impact approximation 37
II.4 BEYOND THE IMPACT APPROXIMATION 40
II.5 EFFECTS OF THE RADIATOR TRANSLATIONAL MOTION 42
II.6 COLLISION-INDUCED SPECTRA 45
II.7 CONCLUSION 50
APPENDICES 50
II.A Spectral and time domain profiles in various spectroscopies 50
1. Absorption, emission, and dispersion 50
2. Rayleigh and spontaneous Raman scatterings 52
3. Nonlinear Raman spectroscopies 55
4. Time-resolved Raman spectroscopies 59
II.B Some criteria for the approximations 61
1. The large number of perturbers 61
2. The local thermodynamic equilibrium 62
3. The binary collisions 64
4. The (full) impact assumption 66
II.C The impact relaxation matrix 67
1. Analysis through the time dependence 67
2. Analysis through the frequency dependence 71
II.D The Liouville space 72
II.E The resolvent approach 75
1. Spectral-shape expression 75
2. Rotational invariance 77
3. Detailed balance 78
CHAPTER III ISOLATED LINES 80
III.1 INTRODUCTION 80
III.2 DOPPLER BROADENING AND DICKE NARROWING 90
III.2.1 The Doppler broadening 91
III.2.2 The Dicke narrowing 92
III.3 BASIC MODELS FOR SPECTRAL LINE SHAPES 94
III.3.1 The Lorentz profile 94
III.3.2 The Dicke profile 95
III.3.3 The Voigt profile 96
III.3.4 The Galatry profile 97
III.3.5 The Nelkin-Ghatak profile 98
III.3.6 Correlated profiles 100
III.3.7 Characteristics of the basic profiles 102
III.4 SPEED-DEPENDENT LINE-SHAPE MODELS 107
III.4.1 Observation of speed-dependent inhomogeneous profiles 107
III.4.2 Basic speed-dependent profiles 115
III.4.3 The Rautian-Sobelman model 121
III.4.4 The Keilson-Storer memory model 131
III.5 AB INITIO APPROACHES OF THE LINE SHAPE 143
III.5.1 The Waldmann-Snider kinetic equation 143
III.5.2 The generalized Hess method 145
III.5.3 Collision kernel method 147
III.5.4 Approaches from a simplified Waldmann-Snider equation 150
III.6 CONCLUSION 156
APPENDIX 157
III.A Computational aspects 157
1. Algorithms for the Voigt and Galatry profiles 157
2. Computation of speed-dependent profiles 159
CHAPTER IV COLLISIONAL LINE MIXING (WITHIN CLUSTERS OF LINES) 164
IV.1 INTRODUCTION 164
IV.2 THE SPECTRAL SHAPE 171
IV.2.1 Approximations and general expressions 171
IV.2.2 Asymptotic expansions 175
IV.2.3 Computational aspects and recommendations 186
IV.3 CONSTRUCTING THE IMPACT RELAXATION MATRIX 190
IV.3.1 Simple empirical (classical) approaches 191
IV.3.2 Statistically based energy gap fitting laws 198
IV.3.3 Dynamically based scaling laws 205
IV.3.4 Semi-classical models 216
IV.3.5 Quantum models 228
IV.4 DETERMINING LINE-MIXING PARAMETERS FROM EXPERIMENTS 235
IV.4.1 Introduction 235
IV.4.2 Relaxation matrix elements 239
IV.4.3 First-order line-coupling coefficients 241
IV.4.4 Mixed theoretical model and measured spectra fitting approaches 244
IV.5 LITERATURE REVIEW 244
IV.5.1 Available line-mixing data 245
IV.5.2 Comparisons between predictions and laboratory measurements 246
IV.5.3 Comparisons between predictions and atmospheric measurements 249
IV.6 CONCLUSION 249
APPENDICES 250
IV.A Vibrational dephasing 250
IV.B Perturbed wave functions 254
IV.C Resonance broadening 255
CHAPTER V THE FAR WINGS (BEYOND THE IMPACT APPROXIMATION) 258
V.1 INTRODUCTION 258
V.2 EMPIRICAL MODELS 260
V.2.1 The . factor approach 260
V.2.2 The tabulated continua 263
V.2.3 Other approaches 265
V.3 FAR WINGS CALCULATIONS: THE QUASISTATIC APPROACH 265
V.3.1 General expressions 266
V.3.2 Practical implementation and typical results 269
V.3.3 The band average line shape: back to the . factors 272
V.4 FROM RESONANCE TO THE FAR WING: A PERTURBATIVE TREATMENT 274
V.4.1 General expressions 274
V.4.2 Illustrative results 276
V.5 FROM RESONANCE TO THE FAR WING: A NON-PERTURBATIVE TREATMENT 278
V.5.1 General expression 278
V.5.2 Illustrative results 280
V.6 CONCLUSION 282
APPENDIX 283
V.A The water vapor continuum 283
1. Definition, properties and semi-empirical modeling of the H2O continuum 285
2. On the origin of the water vapor continua 286
3. The self- and N2-broadened continua within the .2 band 288
4. Conclusion 289
CHAPTER VI COLLISION-INDUCED ABSORPTION AND LIGHT SCATTERING 292
VI.1 INTRODUCTION 292
VI.2 COLLISION-INDUCED DIPOLES AND POLARIZABILITIES FOR DIATOMIC MOLECULES 293
VI.3 COLLISION-INDUCED SPECTRA IN THE ISOTROPIC APPROXIMATION 294
VI.3.1 Two illustrative examples: H2 and N2 294
VI.3.2 Modeling of the line shape 298
VI.4 EFFECTS OF THE ANISOTROPY OF THE INTERACTION POTENTIAL 301
VI.5 THE IMPORTANCE OF BOUND AND QUASIBOUND STATES IN CIA SPECTRA 307
VI.6 INTERFERENCE BETWEEN PERMANENT AND INDUCED DIPOLES (CIA) OR POLARIZABILITIES (CILS) 310
VI.6.1 Depolarized light scattering spectra of H2 and N2 311
VI.6.2 The HD problem 313
VI.6.3 Intercollisional dips 317
VI.7 CONCLUSION 318
CHAPTER VII CONSEQUENCES FOR APPLICATIONS 320
VII.1 INTRODUCTION 320
VII.2 BASIC EQUATIONS 321
VII.2.1 Radiative heat transfer 321
VII.2.2 Remote sensing 324
VII.3 ISOLATED LINES 328
VII.3.1 The basic Lorentz and Voigt profiles 328
VII.3.2 More refined isolated line profiles 331
VII.4 LINE MIXING WITHIN CLUSTERS OF LINES 335
VII.5 ALLOWED BAND WINGS AND CIA 342
VII.5.1 Allowed band wings 342
VII.5.2 Collision-induced absorption 348
VII.6 CONCLUSION 350
CHAPTER VIII TOWARD FUTURE RESEARCHES 352
VIII.1 INTRODUCTION 352
VIII.2 DICKE NARROWING IN SPEED-DEPENDENT LINE-MIXING PROFILES 352
VIII.2.1 Models of profiles in the hard collision frame 352
VIII.2.2 Experimental tests in multiplet spectra 356
VIII.3 FROM RESONANCES TO THE FAR WINGS 360
VIII.3.1 Semi-classical approach 361
VIII.3.2 Generalized scaling approach 365
VIII.4 TOMORROW'S SPECTROSCOPIC DATABASES 365
VIII.4.1 Isolated lines 366
VIII.4.2 Line mixing 368
VIII.4.3 Far-wings and collision-induced absorption 369
VIII.5 CONCLUSION 371
APPENDIX 374
ABBREVIATIONS AND ACRONYMS 374
SYMBOLS 377
UNITS AND CONVERSIONS 379
REFERENCES 382
SUBJECT INDEX 426

Produkt-Details

• Erscheint lt. Verlag: 12.8.2008
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie ► Analytische Chemie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Atom- / Kern- / Molekularphysik
• Themenwelt: Technik
• ISBN-10: 0-08-056994-3 / 0080569943
• ISBN-13: 978-0-08-056994-9 / 9780080569949