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Title:VIibration-rotation analysis of the 13CO2 Asymmetric stretch fundamental band in ambient air for the physical teaching laboratory
Author(s):Dolson, David A.
Contributor(s):Anders, Catherine B.
Subject(s):Mini-symposium: Spectroscopy in the Classroom
Abstract:The chem{CO_2} asymmetric stretch fundamental band near 4.3 $mu$m is one of the strongest infrared absorption transitions of all small molecules. This band is an undesired interference in most infrared spectra, but it also serves as a potential choice for a vibration-rotation analysis experiment in the physical chemistry teaching laboratory. Due to the strength of this band and the 1.1% natural abundance of carbon-13, the asymmetric stretch fundamental band of $^{13}$chem{CO_2} is readily observable in a typical ambient air background spectrum and is shifted sufficiently from the stronger $^{12}$chem{CO_2} fundamental such that the $^{13}$chem{CO_2} P-branch lines are almost completely free of interferences and are easily assigned. All of the $^{13}$chem{CO_2} R-branch lines appear within the $^{12}$chem{CO_2} P-branch, which creates assignment challenges. Students in our program have analyzed the $^{13}$chem{CO_2} fundamental asymmetric stretch band over a two-year period. Analyses of the P-branch line positions enabled the prediction of additional R-branch line positions, which guided line identification and measurements in the $^{13}$chem{CO_2} R-branch. C=O bond lengths determined from analyses of the $^{13}$chem{CO_2} spectra improved when R-branch lines were added to the initial P-branch data sets. Spectral appearance, analyses and results will be presented for spectra obtained at 0.5 cm$^{-1}$ resolution and at 0.125 cm$^{-1}$ resolution. The challenge of predicting and finding the $^{13}$chem{CO_2} R-branch lines among other interfering lines adds an element of realism to this experiment that is not found in many student experiments of this type.
Issue Date:25-Jun-15
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:ACS
Date Available in IDEALS:2016-01-05

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