Collisional Effects on Molecular Spectra

by Hartmann; Boulet; Robert

• ISBN13: 9780444520173
• ISBN10: 0444520171
• Format: Hardcover
• Copyright: 2008-08-12
• Publisher: Elsevier Science

Summary

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 1000 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

Author Biography

Jean-Michel Hartmann, Directeur de Recherche au CNRS, Laboratoire Inter-universitaire des Systemes Atmospheriques, Universites Paris VII, Paris XII et CNRS, Faculte des Sciences et Technologie, 61 avenue du General de Gaulle, 94010 Creteil Cedex, France Christian Boulet, Professeur des Universites, Laboratoire de PhotoPhysique Moleculaire, Universite Paris XI et CNRS, Campus d'Orsay (batiment 350), 91405 Orsay Cedex, France Daniel Robert, Professeur emerite des Universites, Institut UTINAM, Universite de Franche-Comte et CNRS, UFR Sciences Techniques, 16 route de Gray, 25030 Besancon Cedex, France

Table of Contents

Foreword	p. xiii
Acknowledgments	p. xv
Introduction	p. 1
General Equations	p. 9
Introduction	p. 9
Dipole Autocorrelation Function	p. 10
General formalism	p. 10
The Hamiltonian of the molecular system	p. 13
Toward "Conventional" Impact Theories	p. 16
General properties of the correlation function	p. 16
The binary collision approximation	p. 17
Initial statistical correlations	p. 19
The impact approximation	p. 20
Beyond the Impact Approximation	p. 23
Effects of the Radiator Translational Motion	p. 25
Collision-Induced Spectra	p. 28
Conclusion	p. 33
Appendices
Spectral and time domain profiles in various spectroscopies	p. 33
Absorption, emission, and dispersion	p. 33
Rayleigh and spontaneous Raman scatterings	p. 35
Nonlinear Raman spectroscopies	p. 38
Time-resolved Raman spectroscopies	p. 42
Some criteria for the approximations	p. 44
The large number of perturbers	p. 44
The local thermodynamic equilibrium	p. 45
The binary collisions	p. 47
The (full) impact assumption	p. 49
The impact relaxation matrix	p. 50
Analysis through the time dependence	p. 50
Analysis through the frequency dependence	p. 54
The Liouville space	p. 55
The resolvent approach	p. 58
Spectral-shape expression	p. 58
Rotational invariance	p. 60
Detailed balance	p. 61
Isolated Lines	p. 63
Introduction	p. 63
Doppler Broadening and Dicke Narrowing	p. 73
The Doppler broadening	p. 74
The Dicke narrowing	p. 75
Basic Models for Spectral Line Shapes	p. 77
The Lorentz profile	p. 77
The Dicke profile	p. 78
The Voigt profile	p. 79
The Galatry profile	p. 80
The Nelkin-Ghatak profile	p. 81
Correlated profiles	p. 83
Characteristics of the basic profiles	p. 85
Speed-Dependent Line-Shape Models	p. 90
Observation of speed-dependent inhomogeneous profiles	p. 90
Basic speed-dependent profiles	p. 98
The Rautian-Sobelman model	p. 104
The Keilson-Storer memory model	p. 114
AB Initio Approaches of the Line Shape	p. 126
The Waldmann-Snider kinetic equation	p. 126
The generalized Hess method	p. 128
Collision kernel method	p. 130
Approaches from a simplified Waldmann-Snider equation	p. 133
Conclusion	p. 139
Appendix
Computational aspects	p. 140
Algorithms for the Voigt and Galatry profiles	p. 140
Computation of speed-dependent profiles	p. 142
Collisional Line Mixing (Within Clusters of Lines)	p. 147
Introduction	p. 147
The Spectral Shape	p. 154
Approximations and general expressions	p. 154
Asymptotic expansions	p. 158
Computational aspects and recommendations	p. 169
Constructing the Impact Relaxation Matrix	p. 173
Simple empirical (classical) approaches	p. 174
Statistically based energy gap fitting laws	p. 181
Dynamically based scaling laws	p. 188
Semi-classical models	p. 199
Quantum models	p. 211
Determining Line-Mixing Parameters from Experiments	p. 218
Introduction	p. 218
Relaxation matrix elements	p. 222
First-order line-coupling coefficients	p. 224
Mixed theoretical model and measured spectra fitting approaches	p. 227
Literature Review	p. 227
Available line-mixing data	p. 228
Comparisons between predictions and laboratory measurements	p. 229
Comparisons between predictions and atmospheric measurements	p. 232
Conclusion	p. 232
Appendices
Vibrational dephasing	p. 233
Perturbed wave functions	p. 237
Resonance broadening	p. 238
The Far Wings (Beyond the Impact Approximation)	p. 241
Introduction	p. 241
Empirical Models	p. 243
The x factor approach	p. 243
The tabulated continua	p. 246
Other approaches	p. 248
Far Wings Calculations: The Quasistatic Approach	p. 248
General expressions	p. 249
Practical implementation and typical results	p. 252
The band average line shape: back to the x factors	p. 255
From Resonance to the Far Wing: A Perturbative Treatment	p. 257
General expressions	p. 257
Illustrative results	p. 259
From Resonance to the Far Wing: A Non-Perturbative Treatment	p. 261
General expression	p. 261
Illustrative results	p. 263
Conclusion	p. 265
Appendix
The water vapor continuum	p. 266
Definition, properties and semi-empirical modeling of the H[subscript 2]O continuum	p. 268
On the origin of the water vapor continua	p. 269
The self- and N[subscript 2]-broadened continua within the v[subscript 2] band	p. 271
Conclusion	p. 272
Collision-Induced Absorption and Light Scattering	p. 275
Introduction	p. 275
Collision-Induced Dipoles and Polarizabilities for Diatomic Molecules	p. 276
Collision-Induced Spectra in the Isotropic Approximation	p. 277
Two illustrative examples: H[subscript 2] and N[subscript 2]	p. 277
Modeling of the line shape	p. 281
Effects of the Anisotropy of the Interaction Potential	p. 284
The Importance of Bound and Quasibound States in CIA Spectra	p. 290
Interference Between Permanent and Induced Dipoles (CIA) or Polarizabilities (CILS)	p. 293
Depolarized light scattering spectra of H[subscript 2] and N[subscript 2]	p. 294
The HD problem	p. 296
Intercollisional dips	p. 300
Conclusion	p. 301
Consequences for Applications	p. 303
Introduction	p. 303
Basic Equations	p. 304
Radiative heat transfer	p. 304
Remote sensing	p. 307
Isolated Lines	p. 311
The basic Lorentz and Voigt profiles	p. 311
More refined isolated line profiles	p. 314
Line Mixing within Clusters of Lines	p. 318
Allowed Band Wings and CIA	p. 325
Allowed band wings	p. 325
Collision-induced absorption	p. 331
Conclusion	p. 333
Toward Future Researches	p. 335
Introduction	p. 335
Dicke Narrowing in Speed-Dependent Line-Mixing Profiles	p. 335
Models of profiles in the hard collision frame	p. 335
Experimental tests in multiplet spectra	p. 339
From Resonances to the Far Wings	p. 343
Semi-classical approach	p. 344
Generalized scaling approach	p. 348
Tomorrow's Spectroscopic Databases	p. 348
Isolated lines	p. 349
Line mixing	p. 351
Far-wings and collision-induced absorption	p. 352
Conclusion	p. 354
Appendix	p. 357
Abbreviations and Acronyms	p. 357
Symbols	p. 360
Units and Conversions	p. 362
References	p. 365
Subject Index	p. 409
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