VIibration-rotation analysis of the 13CO2 Asymmetric stretch fundamental band in ambient air for the physical teaching laboratory

Dolson, David A.

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https://hdl.handle.net/2142/79265 Copy

Description

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.

Issue Date

25-Jun-15

Keyword(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.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

Permalink

http://hdl.handle.net/2142/79265

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