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Title:A Re-examination Of The Quantitative Infrared Absorption Cross-sections Of Isobutane
Author(s):Blake, Thomas A.
Contributor(s):Myers, Tanya L.; Johnson, Timothy J.; Sams, Robert L.; Sharpe, Steven W.; Hughey, Kendall D.
Abstract:Recently published work\footnote {DM Hewett, PF Bernath, BE Billinghurst. 2019 “Infrared absorption cross sections of isobutane with hydrogen and nitrogen as broadening gases.” \emph{Journal of Quantitative Spectroscopy and Radiative Transfer} 227:226–229.} has called into question the absolute infrared absorption cross-section values for isobutane presented in the Northwest Infrared (NWIR) database. As a result, we have remeasured these cross-sections. In all, four data sets were acquired, analyzed and compared to the original NWIR database with excellent agreement. All new data sets were measured with a nominal pathlength of 20 cm and sample temperature of 25.0 $^{\circ}$C. Three data sets were acquired using a Bruker IFS 125HR spectrometer equipped with a HgCdTe detector. Spectra were first recorded between 600 and 5000 \wn at 0.112 \wn instrument resolution using thirteen burdens of isobutane (0.3 to 22 Torr), each pressure-broadened to one atmosphere using N$_{2}$ gas. The second and third data sets were recorded using thirteen burdens of isobutane (0.1 to 23 Torr), at an instrument resolution of 0.01 \wn. A spectrum of each sample was recorded neat and then recorded pressure-broadened to one atmosphere using N$_{2}$ gas, producing two data sets. A fourth data set, using eleven burdens of neat isobutane (0.5 to 23 Torr) was recorded using a Bruker IFS 66v/S with a DTGS detector. Spectra were recorded between 400 and 6500 \wn at 2 \wn instrument resolution. Each of the four data sets was fitted using a weighted linear least squares algorithm and resulted in a “composite” log$_{10}$ absorbance spectrum of isobutane with concentration-pathlength units of ppm$^{-1}$ m$^{-1}$. The wavenumber axis is in units of \wn. For the 125HR data sets, the integrated band strengths for both the C-H stretch and CH$_{2}$ bend regions are within 2\% of the original NWIR integrated band strengths, and the 66v/S integrated band strengths for both spectral regions are within 5\% of the NWIR data. The agreement between the original and new cross-section data is close to the original experimental error, 3\%, reported for the NWIR database.
Issue Date:2021-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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