Gas-Phase Databases for Quantitative Infrared Spectroscopy

TLDR

The National Institute of Standards and Technology (NIST) and the Pacific Northwest National Laboratory (PNNL) are each creating quantitative databases containing the vapor‑phase infrared spectra of pure chemicals. The digital databases were created to support laboratory and remote‑sensing applications. The databases were built at ≈0.1 cm⁻¹ resolution, using ≥9 path‑length–concentration measurements fitted to weighted Beer's law, and compared across 12 diverse samples. Positional uncertainties are ≤0.005 cm⁻¹ and absorbance uncertainties <2 % for most compounds, and the two databases agree within experimental uncertainties across 12 diverse samples, except one case.

Abstract

The National Institute of Standards and Technology (NIST) and the Pacific Northwest National Laboratory (PNNL) are each creating quantitative databases containing the vapor-phase infrared spectra of pure chemicals. The digital databases have been created with both laboratory and remote-sensing applications in mind. A spectral resolution of ≈0.1 cm −1 was selected to avoid degrading sharp spectral features, while also realizing that atmospheric broadening typically limits line widths to 0.1 cm −1 . Calculated positional (wavenumber, cm −1 ) uncertainty is ≤0.005 cm −1 , while the 1σ statistical uncertainty in absorbance values is &lt;2% for most compounds. The latter was achieved by measuring multiple (typically ≥9) path length–concentration burdens and fitting a weighted Beer's law plot to each wavenumber channel. The two databases include different classes of compounds and were compared using 12 samples. Though these 12 samples span a range of polarities, absorption strengths, and vapor pressures, the data agree to within experimental uncertainties with only one exception.