Brent-Experiment 5

Brent-Experiment 5 - Experiment 5- Vibronic Spectrum of...

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Experiment 5- Vibronic Spectrum of Iodine by UV-Vis Absorption Author: Brent G. Klapthor Group 6 Section 4, Tues 11:00 AM - 2:00 PM Partner: Jacob Waters 2/22/2011 Abstract: The primary objective of this experiment was to use UV-visible light spectroscopy to investigate the molecular structure of the diatomic iodine molecule. This first involved calculating the relative energies of Iodine in the ground state and excited states. An absorption spectrum for Iodine was generated through spectroscopy. The difference in vibrational energies could then be plotted against the v’+1 labeled peaks in a Birge-Sponer plot. The intercept of this plot corresponded to the harmonic frequency, ω e , found to be 138.253 cm -1 . The slope was used to calculate the first anharmonicity parameter, ω e x e, to be 1.052 cm -1 . Using equations and correlations discussed the dissociation energy, D e was calculated to be 4611 cm -1 and the Morse parameter, β, to be 1.974 Å. A Morse potential energy graph was constructed, illustrating the relative energy levels of interatomic separations.
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Experiment 5- Vibronic Spectrum of Iodine by UV-Vis Absorption I. Introduction UV-visible light spectroscopy is a method commonly used to investigate the quantum mechanics and atomic structure of elements. In this experiment, one of our goals was to determine the vibrational energy of atomic iodine as internuclear spacing varies. In doing so we were able to identify the equilibrium interatomic radius of iodine, the state the molecule is most commonly found in. In other words, this is the spacing which maximizes entropy, minimizes energy, and thus occurs most frequently in nature. From the raw spectroscopy data, our first task was to generate a Birge-Sponer plot. By graphing the difference between successive vibrational energy states, ΔG v , against (v +1), a line of the form = - ( + ) ∆Gv ωe 2ωexe v 1 was produced where ω e indicates the harmonic frequency and ω e x e is the first anharmonicity parameter which can be found from the intercept and slope of the line respectively. Next, in calculation of the Morse potential, the group had to complete several intermediate calculations such as the dissociation energy, D e , and Morse parameter, β. The Morse parameter equals, = β 8π2cμωexeh where in addition to the variables mentioned above are the constants the speed of light, c, Planck’s constant, h, and the reduced mass, μ. The group used spectroscopy to create calculations for the Vibronic energy levels at a range of interatomic spacing of each iodine molecule. = [ - - ( - )] VR De 1 e β R Re 2 From the Morse Potential graph, the equilibrium radius may be observed. Because molecules are most likely to populate their lowest energy states, we expect the most likely energy levels for Iodine to be the interatomic radius, r, where the Morse Potential V(R) is minimized. In actuality chemical bonds are not perfect harmonic oscillators. As chemical bonds stretch, they weaken and upon compression, interatomic repulsions raise
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This note was uploaded on 03/08/2011 for the course CHEM 232 taught by Professor James during the Spring '11 term at Clemson.

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Brent-Experiment 5 - Experiment 5- Vibronic Spectrum of...

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