Temperature-dependent absorption cross section measurements for propene, 1-butene, cis-/trans-2-butene, isobutene and 1,3-butadiene in the spectral region 8.4–11.7 µm

Abstract

We present a comprehensive study on the temperature-dependent mid-infrared absorption spectra between 8.4 µm and 11.7 µm for a complete list of C3-C4 alkenes, namely propene, 1-butene, cis-/trans-2-butene and isobutene, as well as 1,3-butadiene, from room temperature to roughly 1000 K. The methodology deploys a rapid-tuning, broad-scan external-cavity quantum-cascade laser (EC-QCL) in a shock tube and can provide quantitative absorption information at a rate in excess of 30 cm−1/ms at spectral intervals between 0.35–0.6 cm−1. The experimental procedure was validated with room-temperature, nitrogen-diluted, static spectra measurements for propene, 1-butene, isobutene, and 1,3-butadiene, showing good agreement with existing spectroscopic databases. Spectral measurements were extended to higher temperatures with shock-heated test gas mixtures diluted by argon, at experimental conditions between 600–1000 K and 1.5–2.5 atm. The resulting spectra show strong temperature dependence and represent the first experimental collection of broadband high-temperature absorption spectra for these species. The measured high-temperature spectra are in reasonable agreement with predictions from fixed-wavelength absorption cross section correlations in the literature. The data presented are archived in the Stanford ShockGas-IR database and provide useful expansions of the existing knowledge on molecular absorption in the mid-infrared at elevated temperatures.