The mechanism of CO2 dissociation during entry in the Mars atmosphere is experimentally investigated. A hydrogen-oxygen combustion-driven shock tube is used to simulate physical and chemical conditions in a CO2-N-2 mixture. Two shock velocity/initial pressure conditions are studied: 7.09 +/- 0.05 km /s at 100 Pa (called the low-pressure condition) and 5.68 +/- 0.07 km /s at 300 Pa (called the high-pressure condition). The temperature behind the shock wave is obtained by analyzing the high-temporal-resolution and high-spatial-resolution experimental spectra of the CN violet (B-2 Sigma(+ )-> X-2 Sigma(+), Delta v = 0) system. The CO number density is derived using a tunable diode laser absorption spectroscopy system based on CO absorption near 2.33 mu m. Moreover, a numerical code is developed to reproduce the experimental results (temperatures and species densities). The kinetic code in this work is based on Park's two-temperature model. Comparisons between experiments and calculations are presented. Such a relatively simple two-temperature model fails to accurately describe the nonequilibrium temperature and CO number density but is suitable for equilibrium temperature predictions.