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Outline:

Introduction. The nature of spectra. Atomic hydrogen. Complex atoms. Radiative transitions and helium. Alkali atoms and their spectra. Nebular spectra. X-ray spectra. Isotope effects. Molecular spectra.

Aims:

This module aims to:

•ÌýÌý Ìýunderstand the atomic and molecular processes that give rise to astronomical spectra
•ÌýÌý Ìýextend knowledge of atomic physics and to a lesser extent of quantum physics
•ÌýÌý Ìýbecome familiar with the terminology used by atomic and molecular spectroscopists
•ÌýÌý Ìýdiscuss the emission and absorption of radiation by atoms and molecules, concentrating on line radiation
•ÌýÌý Ìýdiscuss the formation of emission and absorption lines in astronomical objects at all wavelengths from X-rays to radio, including excitation mechanisms
•ÌýÌý Ìýunderstand how spectral features give us information about the properties of the material from which the spectra originate
•ÌýÌý Ìýprovide the background required to understand astronomical applications of spectroscopy in other 3rd year and 4th year modules including observational astronomy practicals and lecture modules in astrophysics

Intended Learning Outcomes:

On successful completion of this module, students should be able to:

•ÌýÌý Ìýidentify astronomical spectral lines and interpret how they are formed
•ÌýÌý Ìýoutline the principles of the structure of atoms, including: electronic and nuclear angular momenta, the exclusion principle and electron shells; fine and hyperfine structure
•ÌýÌý Ìýdiscuss the processes of emission and absorption of radiation by atoms, defining the oscillator strength and the Einstein coefficients, and including: recombination and ionization; selection rules; forbidden transitions; fine and hyperfine structure transitions; autoionization; inner shell transitions
•ÌýÌý Ìýexplain the electronic, vibrational and rotational structure and spectra of diatomic molecules, including an outline of angular momentum coupling schemes
•ÌýÌý Ìýdiscuss astronomical applications of atomic and molecular spectroscopy, at all wavelengths from X-rays to the radio and in all types of object, indicating the types of result that can be obtained and including consideration of excitation mechanisms

Teaching and Learning Methodology:

This module is delivered via weekly lectures supplemented by additional discussion.

In addition to timetabled lectures, it is expected that students engage in self-study in order to master the material. This can take the form, for example, of practicing example questions and further reading in textbooks and online.

Indicative Topics:

1.ÌýÌý ÌýIntroduction: The history of spectroscopy

2.ÌýÌý ÌýThe nature of spectra: Astronomical spectra. Energy levels, absorption and emission spectra. Transitions, oscillator strengths, Einstein coefficients, optical thickness.

3.ÌýÌý ÌýAtomic hydrogen: Recap of the H-atom Schrödinger equation and wave functions, quantum numbers. Stellar spectra. Series and limits. Continuum spectra. Pressure effects. Selection rules. Recombination and radio lines. Angular momentum coupling. Fine structure. Hyperfine structure and 21 cm line. Metastable states. Nebulae and ionization structure.

4.ÌýÌý ÌýComplex atoms: Central field model and orbital approximation. Pauli Principle. Electron configurations and the Periodic Table. Ions. Angular momentum: L-S and j-j coupling. Spectroscopic notation: terms and levels, parity. Hund’s rules. Equivalent electrons and the N-atom.

5.ÌýÌý ÌýRadiative transitions and helium: Rigorous and propensity selection rules. Helium spectra. HeII. HeI. Selection rules. Intercombination and forbidden lines. Astrophysical applications. Grotrian diagrams.
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6.ÌýÌý ÌýAlkali atoms and their spectra: Quantum defect. Alkali spectra. Sodium spectral series. Spin-orbit interactions. Selection rules. Astronomical spectra.

7.ÌýÌý ÌýNebular spectra: Ionization structure of planetary nebulae. Excitation mechanisms and pumping. Critical density. UV and visible lines, recombination lines. OIII and the Bowen mechanism. Two valence electrons. Autoionization. Dielectronic recombination.

8.ÌýÌý ÌýX-ray spectra: Inner shell and valence shell transitions. Solar coronal spectra. Dielectronic satellite lines.

9.ÌýÌý ÌýIsotope effects: Mass effects. Nuclear size effects. Spin effects.

10.ÌýÌý ÌýMolecular spectra: (diatomics only). Dipole moments. Simple electronic structure, vibrations, rotations. Born-Oppenheimer approximation. Potential curves. Labelling of electronic states. Rotational energy levels and selection rules. Vibrational energy levels and selection rules. Fractionation. Isotopes. Distortion and dissociation. Rotation-vibration spectra: selection rules and wavelengths. Level populations. Sample astronomical spectra. Ortho and para H2.