Gas-Phase Chemistry in Space: Harvard Global Health Catalyst summit lecture notes

353 Pages·2019·38.085 MB·English

by  François Lique, Alexandre Faure

Gas-Phase Chemistry in Space
From elementary particles to complex organic molecules
AAS Editor in Chief
Ethan Vishniac, John Hopkins University, Maryland, US
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Gas-Phase Chemistry in Space
From elementary particles to complex organic molecules
Franc¸ois Lique
Universite Le Havre Normandie, France
Alexandre Faure
Universite Grenoble Alpes, France
IOP Publishing, Bristol, UK
ªIOPPublishingLtd2019
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thisworkinaccordancewithsections77and78oftheCopyright,DesignsandPatentsAct1988.
ISBN 978-0-7503-1425-1(ebook)
ISBN 978-0-7503-1426-8(print)
ISBN 978-0-7503-1427-5(mobi)
DOI 10.1088/2514-3433/aae1b5
Version:20190201
AAS–IOPAstronomy
ISSN2514-3433(online)
ISSN2515-141X(print)
BritishLibraryCataloguing-in-PublicationData:Acataloguerecordforthisbookisavailable
fromtheBritishLibrary.
PublishedbyIOPPublishing,whollyownedbyTheInstituteofPhysics,London
IOPPublishing,TempleCircus,TempleWay,Bristol,BS16HG,UK
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Contents
Preface x
Acknowledgements xi
About the Editors xii
Contributors xiv
1 The Chemistry of the Early Universe 1-1
1.1 Cosmological Background 1-1
1.1.1 Energy Exchanges: Radiation and Matter Temperatures 1-5
1.2 Big Bang Nucleosynthesis 1-6
1.3 The Recombination Era 1-8
1.4 Chemistry 1-11
1.4.1 Chemical Models 1-11
1.4.2 Formation and Destruction Processes 1-13
1.4.3 Recent Developments in Chemical Modeling 1-15
1.4.4 Non-standard Kinetics 1-19
1.4.5 Cooling Functions 1-20
1.5 Conclusions 1-22
References 1-23
2 Nucleosynthesis: The Origin of the Chemical Elements 2-1
2.1 Introduction 2-1
2.2 Nuclei in the Cosmos 2-2
2.2.1 Solar and Cosmic Abundances 2-2
2.2.2 Cosmic Abundances versus Nuclear Properties 2-4
2.2.3 Overview of Nucleosynthesis 2-6
2.3 Primordial Nucleosynthesis: from H to He 2-7
2.3.1 Thermodynamics of the Early Universe 2-8
2.3.2 BBN: Results and Comparison to Observations 2-10
2.4 Stars: from the Main Sequence to Red Giants 2-14
2.4.1 Basic Stellar Properties 2-14
2.4.2 H burning on the Main Sequence 2-16
2.4.3 He burning in Red Giants 2-18
2.5 Advanced Evolution of Massive Stars 2-20
2.5.1 Neutrino Losses Accelerate Stellar Evolution 2-21
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2.5.2 C, Ne, and O burning 2-23
2.5.3 Si melting and Nuclear Statistical Equilibrium (NSE) 2-25
2.5.4 Overview of the Advanced Evolutionary Phases 2-28
2.6 Explosive Nucleosynthesis in Supernovae 2-30
2.6.1 Main Properties and Classification of Supernovae 2-30
2.6.2 Explosive Nucleosynthesis in Core-collapse Supernovae 2-31
2.6.3 Explosive Nucleosynthesis in Thermonuclear SN 2-35
2.6.4 Production of Intermediate-mass Nuclei (From C to Fe peak) 2-37
2.7 The Heavier-than-Fe Nuclei 2-37
2.7.1 Production Mechanisms and Classification of Isotopes 2-38
2.7.2 The s-process 2-39
2.7.3 The r-process 2-41
2.8 Summary 2-42
References 2-43
3 Gas-phase Chemistry: Reactive Bimolecular Collisions 3-1
3.1 Introduction 3-1
3.2 Basics in Bimolecular Reaction Kinetics 3-3
3.2.1 Interaction Potential—Potential Energy Surface 3-3
3.2.2 Cross Sections and Thermal Rate Coefficients 3-5
3.2.3 Reaction Mechanisms 3-6
3.2.4 Thermodynamic Considerations 3-7
3.2.5 Temperature Dependence of the Thermal Rate Coefficients 3-7
3.3 Experimental Methods 3-9
3.3.1 Total Thermal Rate Coefficient Determination 3-10
3.3.2 Reaction Product Identification and Branching Ratios 3-23
3.4 Theoretical Methods 3-27
3.4.1 Quantum Calculations 3-27
3.4.2 Semi-classical and Statistical Calculations 3-38
3.5 Some Perspectives 3-42
References 3-43
4 Radiative Processes in Astrophysical Molecules 4-1
4.1 Introduction 4-1
4.2 Radiative Transitions 4-2
4.2.1 Photodissociation 4-4
4.2.2 Bound–bound Einstein Coefficients 4-6
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4.2.3 Radiative Association 4-6
4.3 Non-radiative Transitions 4-7
4.3.1 One Dissociative State: Direct Photodissociation 4-9
4.3.2 One Bound State Coupled to Several Dissociative States: 4-10
Predissociation
4.3.3 Small-large Molecule Limits 4-12
4.4 Methods 4-15
4.4.1 Time-independent Close Coupling equations 4-16
4.4.2 Wave Packet Method 4-17
4.5 Electronic Structure Calculations 4-19
4.5.1 Excited Electronic States 4-20
4.5.2 Transition Dipole Moments 4-22
4.5.3 Non-adiabatic Couplings 4-23
4.5.4 Diabatization and Quasi-diabatization 4-23
4.6 Examples 4-25
4.6.1 CO 4-25
4.6.2 HCN 4-27
4.6.3 H CO 4-32
2
4.7 Appendix: Matrix Elements of the G(E) Operator 4-40
4.8 Appendix: Numerical Method for Close Coupling Equations 4-41
References 4-44
5 Electron Collision Processes 5-1
5.1 Introduction 5-1
5.2 Fundamental Processes 5-2
5.2.1 Elastic Scattering 5-3
5.2.2 Rotational Excitation 5-4
5.2.3 Vibrational Excitation 5-7
5.2.4 Electronic Excitation 5-8
5.2.5 Impact Dissociation 5-8
5.2.6 Dissociative Electron Attachment 5-9
5.2.7 Dissociative Recombination 5-10
5.2.8 Electron Impact Ionization 5-12
5.2.9 Electron Impact Dissociative Ionization 5-12
5.3 Methodology 5-12
5.4 Astrophysical Examples 5-15
5.4.1 Dissociative Recombination of H+ 5-15
3
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5.4.2 Electron-impact Excitation of Water 5-16
5.4.3 Electron-impact Rotational Excitation of Molecular Ions: 5-18
+ +
HCO and ArH
5.4.4 Electron-impact Rotational Excitation of CN 5-19
5.4.5 Electron-impact Rotational Excitation of CH+ 5-20
5.5 Sources of Data 5-21
References 5-23
6 Molecular Spectroscopy of Astrophysical Molecules 6-1
6.1 Introduction 6-1
6.2 Molecular Spectroscopy in a Nutshell: Diatomic Molecules 6-6
6.2.1 Vibrational States 6-6
6.2.2 Rotational States 6-9
6.2.3 The Non-rigid Rotor 6-13
6.2.4 Intensities, Populations, and Transition Probabilities 6-15
6.3 Laboratory Rotational Absorption Spectroscopy 6-17
6.3.1 Experimental Setup 6-17
6.4 The Symmetric Rotor 6-21
6.4.1 Energy Terms and Spectra 6-21
6.4.2 Intensities and Remote Sensing 6-25
6.4.3 Toward the Asymmetric Rotor 6-26
6.5 Laboratory Rotational Emission Spectroscopy 6-29
6.5.1 Experimental Setup 6-29
6.6 Molecular Symmetry—Group Theory in a Nutshell 6-31
6.6.1 Introduction, Separation of Variables 6-31
6.6.2 Pauli Principle 6-33
6.6.3 Normal Modes of Molecular Vibration 6-35
6.6.4 Molecular Symmetry Representations 6-38
6.7 Vibrational Spectroscopy 6-44
6.7.1 N O, a Linear Molecule 6-44
2
6.7.2 Vibrational and Rovibrational Spectroscopy 6-47
CH+—A Symmetric Top Molecule
3
6.7.3 Rotational Spectroscopy of an Asymmetric Top 6-53
6.8 Large Amplitude Motion: Tunneling and Internal Rotation 6-56
6.8.1 Tunneling: Chirped-pulse Fourier Transform Spectroscopy 6-56
6.8.2 Internal Rotation: CH Torsion 6-60
3
6.8.3 Rotation Torsion Coupling 6-63
6.8.4 Example: Methacrolein 6-64
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6.9 Astrophysical Spectra 6-66
6.9.1 Propanal: a Complex Molecule Seen with ALMA 6-67
6.9.2 Protonated Hydrogen, H+, Molecules as a Chemical Clock 6-70
3
6.9.3 C+, One Carrier of the DIBs 6-75
60
6.9.4 Molecular Spectroscopy: a Molecular Physics Perspective 6-77
References 6-79
7 Excitation of Astrophysical Molecules 7-1
7.1 Radiative Transitions 7-2
7.2 Non-LTE Situations 7-6
7.3 Collisional Transitions 7-12
7.3.1 Calculation and Fitting of Potential Energy Surfaces 7-14
7.3.2 Time-independent Quantum Scattering Calculations 7-18
7.3.3 Hyperfine Transitions 7-25
7.4 Excitation of Interstellar Molecules 7-25
References 7-27
8 Applications: the Molecular Viewpoint of Interstellar 8-1
Observations
8.1 Introduction 8-1
8.2 Importance of Accurate Molecular Data 8-5
8.2.1 Spectroscopy 8-6
8.2.2 Chemical Reactivity 8-8
8.2.3 Quantum Chemistry 8-8
8.2.4 Laboratory Confirmation 8-10
8.3 Success and Limitations of Gas-phase Chemistry 8-10
8.3.1 Successful Achievements of Gas-phase Chemical Models 8-12
8.3.2 The Limitations of Gas-phase Chemistry 8-26
8.3.3 Complex Organic Molecules 8-28
8.4 The Importance of Surface Chemistry 8-29
8.4.1 Bottom-up versus Top-down Chemistry 8-30
8.4.2 The Sulfur Problem 8-31
8.5 Conclusions 8-32
Acknowledgements 8-32
References 8-32
ix