Infrared Spectrum of Ozone
Author: J. M. McCormick
Last Update: February 5, 2014
Introduction
This exercise is identical to the experiment found reference1, except that you will be using O3 instead of SO2, which will be synthesized directly from O2 by a sparkless electrical discharge. Note that some of the description of the IR spectrum of SO2 given in reference 1 may, or may not, apply to O3. It is recommended that you attempt some sort of theoretical modeling to complement the information given in reference 1 to assign the IR spectrum of O3 to specific vibrational modes. For additional information on the relevance of the normal modes of O3, please see references 2-5 and references therein.
Experimental
You will be using the Nicolet Avatar FTIR in the Advanced Laboratory Instrument room running the OMNIC software package again. Please see the HCl-DCl exercise for more information on how to operate this instrument.
You will again use the 10-cm IR gas cell and fill it by purging it with the gas to be analyzed (approximately 5% O3 with the balance being O2). The instructor will demonstrate how to operate the ozone generator. You may have to dilute the O3 in the cell by either withdrawing some O3 or purging the cell briefly with N2 to remove some O3 from the cell in order to bring the signals on-scale.
For the computational component you use should use WebMO.6 Remember to describe the quantum mechanical calculations in the Experimental section of your report. It is suggested that you perform at least a geometry optimization and a vibrational calculation on O3 starting with Hartree-Fock theory with the routine basis set (which should give reasonable results for O3). However, it is suggested that you explore how sensitive your calculated frequencies are to the theory and basis set used. A density functional approach (e. g., B3LYP) or one of the theories described in the HCl-DCl exercise may be a good starting point. Note that Gaussian7 cannot predict whether a Fermi resonance will occur or whether any overtones will be observed; you will have to determine this from your data.
Results and Analysis
Assign the IR spectrum of O3 (determine which transition corresponds to which normal mode or other transition). You will need to have a figure, or figures, that clearly show the different bands and explain how you came to your assignments (helpful hint: simply saying that somebody else assigned it that way will not be sufficient). Comment on how the O3spectrum differs from the SO2 spectrum and whether your calculated molecular parameters (e. g., bond angle) are consistent with literature values. Comment on the assignments of vibrational structure observed in ozone’s electronic transitions noted in references 2-5.
1. Halpern, A. M. and McBane, G. C. Experimental Physical Chemistry: A Laboratory Textbook, 3rd Ed.; Freeman: New York, 2006; p. 37.1-37.7.
2. Xie, D.; Guo, H. and Peterson, K. A. J. Chem. Phys. 2001, 115, 10404-10408. Click here to obtain this reference as a PDF file (Truman addresses and J. Chem. Phys. subscribers only).
3. Grebenschchikov, S. Yu.; Schinke, R.; Qu, Z.-W. and Zhu, H. J. Chem. Phys. 2006, 124, 204313-204325. Click here to obtain this reference as a PDF file (Truman addresses and J. Chem. Phys. subscribers only).
4. O’Keeffee, P.; Ridley, T.; Lawley, K. P. and Donovan, R. J. J. Chem. Phys. 2001, 115, 9311-9319. Click here to obtain this reference as a PDF file (Truman addresses and J. Chem. Phys. subscribers only).
5. Qu, Z.-W.; Zhe, H.; Tashiro, M.; Schinke, R. and Farantos, S. C. J. Chem. Phys. 2004, 120, 6811-6814. Click here to obtain this reference as a PDF file (Truman addresses and J. Chem. Phys. subscribers only).
6a. Polik, W. F and Schmidt, J. R. WebMO Pro 6.1.010p; WebMO LLC: Holland, MI, 2006.
b. Polik, W. F. and Schmidt, J. R. WebMO User’s Guide; 2003,http://www.webmo.net/download/WebMO_Users_Guide.pdf.
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