High-temperature argon broadening of CO₂ near 2190 cm⁻¹ in a shock tube

Abstract

Scanned-wavelength laser absorption measurements of CO₂ diluted in Ar were performed behind reflected shock waves at high temperatures (1158–2017 K) and low pressures (5.1–108.4 kPa). High-resolution (0.001 cm⁻¹) scans were conducted in 0.4-cm⁻¹ increments from about 2188.8 to 2191.8 cm⁻¹ at a scan rate of 2 kHz. The HITRAN 2004, HITRAN 2012, and CDSD-296 databases were all found to underestimate the absorption, typically by an order of magnitude or more. The HITEMP database, however, closely predicted the measured data. For the assumed form $\gamma_{{{\text{CO}}_{ 2} - {\text{Ar}}}} (T) = \gamma_{{{\text{CO}}_{ 2} - {\text{Ar}}}} (T_{0} )(T_{0} /T)^{n}$ with $T_{0}$ = 296 K, an optimization routine was implemented to determine the values of $\gamma_{{{\text{CO}}_{ 2} - {\text{Ar}}}} (T_{0} )$ and $n$. From the optimization, values of 0.033 ± 0.004 cm⁻¹ atm.⁻¹ and 0.61 ± 0.04 were determined for $\gamma_{{{\text{CO}}_{ 2} - {\text{Ar}}}} (T_{0} )$ and $n$, respectively, which are in good agreement with historical values. These values describe an average CO₂–Ar broadening coefficient in the frequency range studied herein and are reliable within the experimental temperature range. In addition, a set of fixed-wavelength measurements at 2190.0175 cm⁻¹ were carried out at 122, 446, and 1115 kPa between 1100 and 2100 K, and the HITEMP predictions incorporating the proposed Ar-broadening parameters showed excellent agreement with these data.