Learning objectives
Application of some key concepts of quantum mechanics and their use in spectroscopy. Becoming familiar with some spectroscopic techniques (UV-visible absorption and fluorescence FT-IR, Raman). Interpretation of spectroscopic data and their use to obtain molecular parameters.
Prerequisites
The same as those of Chemical Physics 2
Course unit content
UV-Vis spectrometer. Raman spectrometer. Notes on Fourier transform; Michelson interferometer spectrometer and FT-IR
Model of particle in a box potential. Applying a pi-conjugated organic molecules.
Born-Oppenheimer approximation.
Theory of groups: group definition, symmetry groups, symmetry elements, reducible and irreducible representations. Reduction of representations. Connection with the quantum-mechanical.
Basics of molecular spectroscopy. Selection rules.
Definition of the normal modes of vibration, the symmetry of the normal modes of vibration (with examples). Use of symmetry for the evaluation of integrals important as mechanical. Selection rules for IR spectroscopy. Raman spectroscopy and its selection rules. Prediction of IR and Raman spectra of molecules of different symmetry.
Calculation methods for quantum-mechanical electronic structure of molecules (notes). Huckel method: approximations, problem solving and calculation of atomic charges, bond orders, dipole moments. 4n +2 rule, use of symmetry.
Laboratory experiments
1) electronic spectra of dyes pi-conjugated and the model of the particle in a box
Recording the spectrum of visible-NIR absorption of organic dyes of increasing length. Interpretation of results based on the model of the particle in a box potential.
2) Absorption spectra and fluorescence of organic dyes. Vibronic structure
Recording the absorption spectrum of electronic and flurescenza of fluorescein, and analysis of the vibronic structure
3) Fluorescence of a molecule excited at two different wavelengths: Kasha's rule
Recording of the absorption spectrum, and two fluorescence spectra excited at two different wavelengths. According to the rule of Kasha, the output will be the same in both cases.
4) Infrared and Raman spectra of inorganic salts having anions of different symmetry
Registration of IR and Raman spectra of solid samples. Interpretation of the spectra using group theory.
5) Calculation of the electronic structure of an unsaturated hydrocarbon by the Hückel method (operation to the computer)
The exercise consists in solving the electronic structure of a greek pi-unsaturated hydrocarbon using the Hückel method. In addition to the energies of the states, we will derive even bond orders and net atomic charges. Through the use of group theory, we will identify the kind of symmetry of the molecular orbitals and therefore the symmetries of the ground state and excited states, and the selection rules for electronic spectroscopy.
Full programme
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Bibliography
P. W. Atkins, Molecular Quantum Mechanics, Oxford University Press
F. A. Cotton, Group Theory in Chemistry
Teaching methods
Oral lessons, exercises, and laboratory experiments
Assessment methods and criteria
Oral examination (together with Chemical Physics 2)
Other information
The written reports of the laboratory experiments have to completed individually or for each group, and have to be given to the teacher at least a week in advance with respect to the examination date. IN ANY CASE the reports have to consigned before the beginning of the next academic year, otherwise the student must enrolle again to the laboratory.
