Rotational and vibrational energy distributions of carbon monoxide, which is liberated during the 193 nm excimer laser ablation of polyimide, have been measured using mass‐resolved resonant multiphoton ionization spectroscopy. Using 150 mJ/cm2 fluence (1000 Å removed per pulse), the rotational temperature is seen to decrease monotonically from 1150 to 650 K from beginning to end of the ablation plume. Additionally, the vibrational temperature is measured to be 3400 K and is constant over time. When using 6 mJ/cm2 to ablate (0.1 Å removed per pulse), the rotational and vibrational temperatures are measured to be 700 and 900 K, respectively. The influence of collisional perturbations and high ablation fluences on the measured rotational and vibrational temperatures is discussed.