Carbon Monoxide Dissociation at Planetary Entry Conditions Examined by Megahertz-Rate Laser Spectroscopy

Abstract

A study of carbon monoxide (CO) dissociation was performed in a shock tube at conditions relevant to the high-speed entry of Venus and Mars atmospheres. The CO number density (or mole fraction) and the temperature are probed behind reflected shock waves at 1 MHz using scanned-wavelength laser absorption spectroscopy near 2011  cm−1 (4.97  μm). The wide range of vibrational states (v=1, 4, 8, and 10) probed by this technique enables precise number density and temperature measurements up to and above 9000 K using a Boltzmann population fit of the resolved spectral lines. Mixtures of CO diluted in Ar at 3–60% are shock-heated in a wide range of conditions (T5=4650−11,150  K at p5=0.26–4.07  atm) and compared to state-of-the-art chemical kinetic models. The time-resolved measurements of temperature and number density behind reflected shock waves are utilized to infer the rate coefficients of CO+M→C+O+M for M=CO, Ar. They are found to be kdiss,CO=1.8×1028⋅T−2.7exp(−129,000/T)  cm3/(mol⋅s) and kdiss,Ar=1.5×1025⋅T−2.1exp(−129,000/T)  cm3/(mol⋅s).