UVVis_Report_AdamRunkle_UMID_46249331

UVVis_Report_AdamRunkle_UMID_46249331 - Experiment 5-...

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Determination of the vibrational transition states for I 2 using Ultraviolet-Visible (UV-Vis) spectroscopy Adam Runkle, 1,* Tim Jin, 1 and Josh Young 1 *Corresponding author: Phone: (269)599-9112 E-mail: [email protected]
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Abstract The various degrees of freedom by which molecules can absorb energy have been well described and include translational, rotational, and vibrational modes. It has been repeatedly shown that each degree of freedom is dependent on intramolecular transitions in the form of electronic, rotational, or vibrational. Ultraviolet-visible (UV-Vis) spectroscopy produces absorbance spectra for molecules, and can be utilized to explicitly determine the energies associated with vibrational transitions of molecular iodine. A sealed sample of iodine absorbs UV-Vis light in a range from 540-590 nm and distinctively yields absorption bands which are characteristic of vibrational transitions from the ground state to the excited state. This experiment utilized such absorption spectra to explicitly determine the ionization energy of the molecule, the convergence limit of quantum vibrational states, the vibrational frequency and anharmonicity of the I2 bond, the dissociation energy of the ground and first excited state, as well as the first transition of the ground state.
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Introduction The variation in the type of molecular transitions—electronic, vibrational, and rotational —has been well established. [1] Considering the distinct separation between such transitions, exploration of the absorption spectra of diatomic molecules can reveal great detail about the electronic quantum states, and it is for this purpose the current experiment was conducted. Electronic transitions from the ground state to an excited state of iodine (I 2 ), as well as other molecules, can be determined by obtaining the absorption spectrum of the diatomic gas at high resolutions. The strength of molecular bonds is an integral part of chemistry and may be determined in a post hoc fashion by observing the absorption of ultraviolet and visible (UV-Vis) light, and utilizing the energies (cm -1 ) at which band heads—produced by the combination of rotational and vibrational transitions—are observed to construct a quantum mechanical diagram of the electronic and vibrational transitions. By conducting such a detailed analysis of the absorption spectra of molecules, scientists and students alike may gain valuable insight into the effectiveness and exactness of the theory of quantum mechanics. Such value is directly seen in the ability to calculate accurately the dissociation energy of the molecule, the vibrational frequency of the molecule, the atomic excitation energy of the molecule, as well as others. This ability to delve deeper into the subatomic structure and mechanics of molecules offers a unique opportunity for scientists to expand on well established theories.
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This note was uploaded on 03/12/2010 for the course CHEM 480 taught by Professor Chen during the Spring '08 term at University of Michigan.

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UVVis_Report_AdamRunkle_UMID_46249331 - Experiment 5-...

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