OPTICAL ABSORPTION
LEARNING OBJECTIVES Each student should be able to: Describe photon absorption; Explain the basic principles that create an absorption spectra; Explain a broaden absorption spectra; Describe the possible fate of optically excited states;
LESSON OUTLINE Absorption/Transmittance; Photon Absorption; Franck-Condon Principle Absorption/Transmittance Spectra; Fate of Excited States
TRANSMITTANCE L a = absorption coefficient I0 (lx ) It(lx ) © Thomson/Brooks Cole L It(lx ) = I0 (lx ) e-aL a = absorption coefficient I0 (lx ) It(lx ) Tunable Laser (lx ) Detector Sample
ABSORPTION & TRANSMISSION SPECTRA http://www.chem.ed.ac.uk/teaching/undergrad/chemistry1/lectures/notes/spectroscopy/spectroscopy%20lectures.pdf
LESSON OUTLINE Absorption/Transmittance; Photon Absorption; Franck-Condon Principle Absorption/Transmittance Spectra; Fate of Excited States
FRANCK-CONDON PRINCIPLE http://www.csus.edu/indiv/m/mackj/chem140b/elecspec.pdf
ABSORPTION SPECTRA When absorption occurs to unbound states of the upper electronic state, the molecule dissociates and the absorption is a continuum. Above the dissociation limit a continuous band of absorption occurs because the final state is an un-quantized translation of the fragments. Below the dissociate limit the electronic spectrum shows a normal vibrational structure. http://www.csus.edu/indiv/m/mackj/chem140b/elecspec.pdf
ABSORPTION STATES As the optical transition becomes less vertical the absorption spectra shift due to the change in the Franck-Condon patterns. http://www.csus.edu/indiv/m/mackj/chem140b/elecspec.pdf
POTENTIAL ENERGY CURVES FOR MOLECULAR OXYGEN http://www.csus.edu/indiv/m/mackj/chem140b/elecspec.pdf
MOLECULAR ORBITALS FOR BENZENE http://faculty.smu.edu/ebiehl/Wade16.ppt
THE ABSORPTION SPECTRUM OF CHLOROPHYLL Red Blue Green http://www.nat.vu.nl/bio/images/fluorescence18062004_1.ppt
TRANSMITTANCE - Aromatic Compounds -
TRANSMITTANCE - Carbonyl Compounds -
BROADENED ABSORPTION SPECTRA http://www.csus.edu/indiv/m/mackj/chem140b/elecspec.pdf
CHROMOPHORES Chromophores are a group of atoms in a molecule that produces color in dyes and other compounds through selective absorption of light, for example, the azo group. Chromophores are components of molecules which absorb light. The wavelength of absorption is related to the size of the chromophores. Smaller chromophores, higher energy (shorter wavelength). They are generally aromatic rings.
LESSON OUTLINE Absorption/Transmittance; Photon Absorption; Franck-Condon Principle Absorption/Transmittance Spectra; Fate of Excited States
FATE OF EXCITED STATES (Primary Photochemical Processes) http://www.csus.edu/indiv/m/mackj/chem140b/elecspec.pdf
PREDISSOCIATION Predissociation is the relaxation to a state with enough energy to break a bond. Predissociation arises when two electronic states cross. Usually one electronic state is stable, and has a well defined potential diagram. The other state is typically a repulsive state. The transition is initially to the stable state, and then transfers across to the repulsive state, where dissociation occurs http://www.csus.edu/indiv/m/mackj/chem140b/elecspec.pdf
DO YOU KNOW WHAT YOU KNOW?
LEARNING OBJECTIVES Each student should be able to: Describe photon absorption; Explain the basic principles that create an absorption spectra; Explain a broaden absorption spectra; Describe the possible fate of optically excited states;