Gas-Phase Databases for Quantitative Infrared Spectroscopy

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 <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.