Vibrational temperatures of CO2 are studied in a pulsed glow discharge by means of time-resolvedin situ Fourier transform infrared spectroscopy, with a 10 μs temporal resolution. A method to analyzethe infrared transmittance through vibrationally excited CO2 is presented and validated on a previouslypublished CO2 spectrum, showing good agreement between fit and data. The discharge under study ispulsed with a typical duty cycle of 5–10 ms on–off, at 50 mA and 6.7 mbar. A rapid increase of thetemperature of the asymmetric stretch vibration (T3) is observed at the start of the pulse, reaching1050 K, which is an elevation of 550 K above the rotational temperature (Trot) of 500 K. After theplasma pulse, the characteristic relaxation time of T3 to Trot strongly depends on the rotationaltemperature. By adjusting the duty cycle, the rotational temperature directly after the discharge isvaried from 530 to 860 K, resulting in relaxation times between 0.4 and 0.1 ms. Equivalently, as thegas heats up during the plasma pulse, the elevation of T3 above Trot decreases strongly.