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Atomic and molecular spectroscopy (CH2209)

Aims

This module aims to present the fundamental principles of spectroscopy, with specific reference to rotational, vibrational and electronic spectra. It describes the elementary absorption and emission processes in atoms and molecules, and outlines the essential selection rules that govern transitions between energy levels. It also illustrates how structural and electronic information can be obtained by analysis of spectra.

General description

This module develops the theory and applications of spectroscopy, from the Schrodinger treatment of electron wave behaviour, through electronic spectroscopy of atoms, rotation and vibrational spectra of molecules. It describes the theory behind each technique, and shows how the spectra obtained can give information about the structure of atoms and molecules, their bonding and energy levels.

Principles of photophysics are also introduced, leading to a description of the actions of lasers and the initiation of photochemical reactions.

Syllabus content

Major features of electronic spectroscopy, absorption of light, molar absorption coefficient, absorbance/transmittance. General factors influencing spectral line widths (collisional, Doppler, Heisenberg) and line intensities (transition probability, population of states, Beer-Lambert law).

Electronic angular momentum, Born-Oppenheimer approximation, Frank-Condon principle and the origin of progressions in electronic spectra. Interpretation of vibrational coarse structure in electronic spectra of diatomics.

Absorption intensity (stimulated and spontaneous processes), Einstein coefficient. Numerical examples of quantum yields and the Stern-Volmer relation will also be covered

Principles of photophysics, including emission and loss processes, fluorescence & phosphorescence, intramolecular energy transfer (IC, ISC), Jablonskii diagrams.

General principles of laser action.

Electrons behaving as waves. Schrodinger equation and its applications to particle-in-the-box and the H atom. Stern-Gerlach experiment and spin angular momentum. Many electron atoms, Russell-Saunders (LS) coupling, atomic term symbols. Atomic selection rules.

Molecular spectroscopy and structure. Microwave spectra, moments of inertia and rotational constants. The rigid diatomic. Types of molecular rotors. Energy levels and allowed transitions.

Infrared spectra: anharmonic oscillator, Morse potential.

Selection rules and rotational fine structure.

Practical work :

A study of the chemical equilibrium by absorption spectrophotometry in the visible region (Fe3+/SCN- system), a study of the Beer-Lambert law and its application to Cr(III) determination, determination of the kinetics of the excited state deprotonation - protonation reaction of 2-napthol by fluorescence spectroscopy, determination of the H-Cl bond length by IR spectroscopy, and UV of gas phase molecules.