Iwona Gulaczyk is an associate professor at the Faculty of Chemistry of Adam Mickiewicz University in Pozna, Poland. Her research focuses on high-resolution molecular spectroscopy of non-rigid molecules with astrophysical significance.Michaël Rey is a senior researcher at CNRS-Université de Bourgogne Europe, France. His research is devoted to the development of numerical and group-theoretical methods for modeling molecular spectra relevant to planetary atmospheres.Ha Tran is a senior researcher at CNRS, Sorbonne Université, Ecole Polytechnique, France. Her research focuses on the effects of intermolecular collisions on molecular gas spectra, specifically for high resolution spectroscopy and atmospheric remote sensing.

• Foreword ixJonathan TENNYSONIntroduction xiiiIwona GULACZYK, Michaël REY and Ha TRAN Chapter 1. Automated Rovibrational Configuration Interaction Calculations 1Subhasish DAS and Guntram RAUHUT1.1. Introduction 11.2. The Hamiltonian 21.3. VSCF/VCI calculations 51.4. RVCI calculations 101.5. Infrared intensities 191.6. Conclusion and outlook 241.7. Acknowledgments 261.8. References 26Chapter 2. Efficient Numerical and Group-Theoretical Methods for Computing Spectra 31Michaël REY2.1. Introduction 312.2. Exploiting symmetry in molecular spectroscopy 322.2.1. Group theory for rigid and nonrigid molecules 332.2.2. Symmetry-adapted functions and irreducible tensor operators 352.3. Variational calculation 422.3.1. Computation of ro-vibrational energy levels by pruning the basis 422.3.2. Nested tensor train contracted basis functions and symmetry 452.4. Hamiltonian for semirigid molecules 492.4.1. ITO formulation of the Eckart–Watson Hamiltonian 492.4.2. ITO formulation of Eckart-frame Hamiltonians in curvilinear coordinates 512.4.3. ITO formulation of ab initio effective Hamiltonians and dipole moment operators 532.5. Hybrid Hamiltonian for non-rigid molecules: ITO formulation of the Hougen–Bunker–Johns formalism 552.6. Calculation of rotation–vibration spectra 582.7. References 59Chapter 3. Isolated Line Shape Theory 65Ha TRAN, Ngoc Hoa NGO and Piotr WCISLO3.1. Introduction 653.2. Doppler broadening and the Gauss profile 673.3. Collisional broadening and shift and the Lorentz and Voigt profiles 683.3.1. Collisional broadening and shift and the Lorentz profile 683.3.2. The usual Voigt profile 683.4. Refined collisional effects and line-shape profiles 713.4.1. Dicke narrowing effect 713.4.2. The speed dependence of line broadening and shift 753.4.3. The Hartmann–Tran profile 783.4.4. The modified Hartmann–Tran profile 823.5. Beyond the impact approximation 863.6. Conclusion 873.7. References 87Chapter 4. Semi-Classical Line-shape Theory 95Robert R. GAMACHE4.1. Introduction 954.2. Semi-classical line-shape theory 974.2.1. From ATC theory to modern semi-classical theories 974.2.2. Collisional line broadening and shifting 984.2.3. Components contributing to the broadening and shifting 1044.2.4. The physics of what is going on 1064.2.5. What does an understanding of the collisional line broadening mechanism tell us? 1094.3. The semi-classical CRBM theory 1124.4. Components of the calculation to be considered 1134.4.1. Trajectory models 1144.4.2. Velocity integration versus mean-relative thermal velocity approximation 1164.4.3. Effect of imaginary components on the pressure-broadened half-width 1164.4.4. The atom–atom component of the intermolecular potential and the effects of its expansion 1184.4.5. Adjusting the atom–atom potential 1214.4.6. Line coupling 1244.5. Temperature dependence of γ and δ 1254.6. Comparison with measurement 1304.7. Speed dependence of γ and δ 1324.8. Vibrational effects 1354.9. Predicting line-shape parameters 1354.10. Conclusion 1394.11. References 140Chapter 5. Ab Initio Calculations of Line-Shape Parameters 153Hubert JÓZWIAK and Piotr WCISLO5.1. Formulation of the line-shape problem 1535.1.1. Derivation of the generalized Waldmann–Snider equation 1595.1.2. State multipoles 1685.1.3. Spectral line shape within the Hess method 1715.1.4. Relation to the phenomenological line-shape models 1775.1.5. Generalizations and other approaches to the spectral line shape problem 1805.2. Quantum scattering theory 1815.3. Application of the fully ab initio approach to molecular systems 1885.4. References 192Chapter 6. Line Mixing Within and Beyond the Impact Approximation 199Christian BOULET and Ha TRAN6.1. Introduction 1996.2. Collisional line mixing within the impact approximation 2026.2.1. Some basic equations 2026.2.2. The weak overlapping regime 2046.2.3. Profile in the near wing of a cluster of lines 2066.2.4. Profile in the near wing of a vibrational band 2076.2.5. Building the impact relaxation matrix 2096.3. Line mixing beyond the impact approximation 2266.3.1. Introduction 2266.3.2. Empirical models: the correcting Χ factor 2276.3.3. Far wings: the quasi-static approach of Rosenkranz 2276.3.4. From resonance to the far wings: non-Markovian ECS model 2316.3.5. Direct predictions from rCMDS (and CMDS) 2346.4. Conclusion 2356.5. References 235Conclusion 243Iwona GULACZYK, Michaël REY and Ha TRANList of Authors 245Index 247Summary of Volume 1A 251