Mars atmospheric entry vehicles have experienced concerning radiative heating at the backshell which could be due to the freezing of recombining \(\text {CO}_2\) in the non-equilibrium regime. The impact of this phenomenon on radiative heating, though highlighted in the recent and past literature, lacks in understanding and characterisation. We present preliminary results for the validation and characterisation of \(\text {CO}_2\) recombination for the conditions representative of low velocity, high density Mars atmospheric entry at the backshell of a spacecraft. The X2 expansion tube in the Cold Driver Assembly at the University of Queensland is used to generate the experimental test conditions. A two dimensional wedge model is used to produce the post shock compression and afterbody expansion which simulates the conditions experienced by the atmospheric entry spacecraft. Mid-wave infrared emission spectroscopic measurements of the 4.3 \(\mu \) m band of \(\text {CO}_2\) were performed to characterise \(\text {CO}_2\) in the pre-shock, post-shock and expanding region. Calibrated results show an increase in the band radiance in the expanding region. The results presented will be used for comparison with and validation of the Eilmer4 numerical simulation software through the RADIS line-by-line radiation code.