CHEM3541 Experiment A - A-1 Study of UV-Visible Spectra of...

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A-1 Study of UV-Visible Spectra of Diphenyl Polyenes Using “Particle -in-a- Box” Model Introduction You may already be aware that molecules and photons can interact in various ways. For example, infrared photons may excite vibrational modes in molecules, while photons in the visible to near ultraviolet region have energies that can excite electrons out of their molecular orbitals into other bound states (formerly unoccupied molecular orbitals). So, each peak in a UV-Visible spectrum corresponds to the excitation of an electron from some occupied molecular orbital to some unoccupied molecular orbital. In this experiment, we shall treat the molecular orbitals in a conjugated carbon-carbon system as one dimensional particle-in-a-box wavefunctions. Transitions from one molecular orbital to another will be treated as transitions from one 1-D particle in a box state to another. The objective of this laboratory experiment is to interpret UV-Visible spectrum of three diphenyl polyenes. The UV- Visible transitions are compared to a particle-in-a-box model and also to transitions calculated using the software package HyperChem. trans,trans-1,4-diphenyl-1,3-butadiene 1,6-diphenyl-1,3,5-hexatriene 1,8-diphenyl-1,3,5,7-octatetraene
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