Rainey_Experiment 5

Rainey_Experiment 5 - Experiment 5: Vibronic Spectrum of...

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Experiment 5: Vibronic Spectrum of Iodine by UV-Vis Absorption Author: Ben Rainey Group 3 Section 1, M 1:25 PM – 4:25 PM Partner: Mark Kalata March 7, 2011 Abstract: The main objective of this experiment was to plot the Morse potential as a function of the internuclear distance for the first excited state of iodine. This experiment uses a UV-Vis spectrophotomer to observe the vibronic spectrum of iodine. The peaks of the iodine absorption spectrum were labeled by comparison to a spectrum of known absorption. The change in vibrational energy was plotted against the quantum level. Utilizing this plot, the harmonic frequency, ω e , and first anharmonicity parameter, ω e x e were both determined. These values were determined to be 140.88 cm -1 and 1.150 cm -1 , respectively. The dissociation energy, D e , and Morse parameter, β, were determined to be 4315 cm -1 and 2.081 Å -1 , respectively. Using these values, a plot of Morse potential, V(R), versus interatomic radius, R, was generated. For a real diatomic molecule, energy levels are not equally spaced and the Morse potential does not follow a perfect parabolic trend and is therefore not a harmonic oscillator. I. Introduction There were two main objectives in this experiment. The first objective of this experiment was to obtain values for the Morse parameter and Dissociation energy for iodine. The second objective was to plot the Morse potential as a function of the internuclear distance for the first excited state of iodine.
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Experiment 5: Vibronic Spectrum of Iodine by UV-Vis Absorption The absorption of different molecules can be shown using UV-Vis absorption. Although it is known that the diatomic structure of iodine is two iodine atoms with a single bond between them, the simple dumbbell model for the occupation of molecular energy levels is not completely accurate. Diatomic iodine does not strictly have the shape of the rigid dumbbell. Molecules vibrate and, by absorbing a photon, can change the arrangement of electrons, thus changing the shape of the molecule. UV-Vis can be used to show the vibrational levels in the ground and excited states of iodine. Analysis of the absorption spectra from the UV-Vis can lead to a detailed description of the inter-atomic potential between two iodine atoms in diatomic iodine. According to the Born-Oppenheimer approximation, each electronic state in a diatomic molecule has a characteristic nuclear potential function, V(R), which relates the interatomic potential energy as a function of interatomic distance, R. For low vibrational energies, the interatomic potential can be simplified to that of a model of a harmonic oscillator. In this model, the potential energy curve would be a parabola and the energy levels would be equally spaced. Real atoms, however, do not behave like an ideal harmonic oscillator. As the interatomic
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Rainey_Experiment 5 - Experiment 5: Vibronic Spectrum of...

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