The vibration-vibration energy transfer of CO
2gas initially excited to the first asymmetric stretch level (00
01) has been observed. Collisional pumping to the (01
11) combination level is measured by monitoring the fluorescence due to the (01
11) → (01
10) band. The rate constant for the process: CO
2(01
11) + CO
2(00
00) → CO
2(00
01) + CO
2(01
10) is found to be

s
-1torr
-1.