The collision-induced rotation–vibration fundamental and first overtone bands of oxygen and nitrogen have been observed in the pure gas at pressures of a few atmospheres, and in mixtures of these gases with argon at pressures of a few tens of atmospheres. From the integrated intensities of the bands it is possible to deduce a value for the first derivative of the quadrupole moment with respect to internuclear distance; we find that |Q′| = 1.6ea₀ for oxygen, and |Q′| = 0.95ea₀ for nitrogen.