Confirmation of PNNL Quantitative Infrared Cross-Sections for Isobutane

Abstract

The Pacific Northwest National Laboratory (PNNL) gas-phase database is a compilation of quantitative experimental (5, 25, and 50 °C) infrared spectra of ca. 500 molecules, designed for in situ, standoff or remote sensing of gases and vapors at or near atmospheric pressure. The data are characterized by calibration on both the wavenumber and intensity axes. Recent papers have called into question the PNNL intensity values for isobutane, [2-methylpropane, HC­(CH3)3], suggesting discrepancies of 30–40%. In this study, we remeasure and re-examine the intensity values of isobutane using both similar and alternate methods to those used to generate the original PNNL database spectra. Indirect confirmation from literature data of homologous molecules and direct confirmation from new results confirm that for many band integrals across the isobutane spectrum, the original PNNL data are indeed accurate to within the reported 3% experimental uncertainty.

Measurement report: Radiative efficiency estimates of (CF3)2CFCN, CF3OCFCF2, and CF3OCF2CF3 using high-resolution Fourier transform infrared spectroscopy

“…and integrated at a 10 cm -1 block interval. We did not observe any dependence of the RE values on the spectral resolution of ACS, which tends to imply a negligible effect of the variation in the linewidth of the ILS on the value of iACS.Johnson et al demonstrated that the iACS of isobutane measured at multiple resolutions between 0.01 and 4.0 cm -1 were in good agreement, thereby implying that resolution dependence did not need to be considered(Johnson et al, 2021). Consequently, RE is indeed an iACS that is weighted by an RF model from 0 to 3000 cm -1 .…”

“…The OPL of MP was calibrated based on HR-FTIR spectroscopy, and its uncertainty was assessed directly. The absorbance measured at high pressures exhibited a different extent of saturation effect according to respective bands, disobeying the linear property of the Beer-Lambert law (Johnson et al, 2021). Therefore, it was critical to use the MP at low partial pressures.…”

“…Nevertheless, we assumed that the iACS of Novec-4710 does not deviate from that obtained when using an N2 broadener. In general, alien gas broadening is considerably smaller than selfbroadening (Johnson et al, 2021). The ACS of Novec-4710 are shown in Fig.…”

“…To get low absorption burdens at the nominal OPL of the MP, the gases to be measured were gravimetrically diluted to a designated concentration with an N2 broadener (the typical gravimetric uncertainty is below 1.5%). This was also required to ensure the accuracy of the pressure readings for trace levels of the absorbing gas (< 0.1 Torr) using pressure gauges, 110 the full scales of which are over 100 Torr (accuracy 0.05 Torr) with a valid dynamic range of 0% to 95% (Johnson et al, 2021).…”

Measurement report: Radiative efficiencies of (CF3)2CFCN, CF3OCFCF2, and CF3OCF2CF3

“…To obtain low absorption burdens at the nominal OPL of the multipass cell, the gases to be measured were gravimetrically diluted to a designated concentration using an N 2 broadener (the typical gravimetric uncertainty is below 1.5 %). This was also required to ensure the accuracy of the pressure readings for trace levels of the absorbing gas (<0.1 Torr) using pressure gauges, the full scales of which are over 100 Torr (accuracy of 0.05 Torr) with a valid dynamic range of 5 % to 95 % (Johnson et al, 2021). The overall signal-to-noise ratios (S/N) of the absorption spectra were higher than 2000.…”