Laser Absorption Spectroscopy Studies of the Cyano Radical for Titan Entry Kinetics

Two near-infrared (NIR) tunable diode laser absorption spectroscopy (TDLAS) diagnostics targeting the cyano radical (CN) near 926 and 1128 nm, respectively, were combined with a multipass absorption spectroscopy ring amplifier to probe varying mixtures of [Formula: see text] dilute in Ar over a wide range of post-reflected-shock temperatures (3200–13,000 K) and pressures (0.1–1.7 atm), allowing isolation of CN formation and decomposition reactions. Nine CN absorption features in the red system were probed at scan rates up to 500 kHz to provide quantitative measurements of species number density profiles behind the reflected shock. The data were analyzed using a detailed mechanism and sensitivity analysis to fit four reactions. The rate coefficients for [Formula: see text] dissociation, [Formula: see text] exchange, and [Formula: see text] dissociation are found to be in reasonably good agreement with prior studies at different temperatures in different mixtures. Of these three, only CN dissociation retained good sensitivity for inference from experimental data, while the other two were floated to optimize fits. In contrast, the measured rate for [Formula: see text] exchange, [Formula: see text], was found to be up to an order of magnitude faster than that provided by the Gökçen reduced Titan mechanism at high temperatures. When the updated rates are applied to measurements in a pure Titan atmosphere mixture, better agreement is found than predicted by the reaction rates from both Gökçen and Slack.