New measurements have been made of rate constants for the vibrational deactivation of N 2 (v = 1) by CH 4 in liquid Ar/liquid N 2 mixtures. The ratio of the liquid phase rate constants, k L , M for the liquid mixture overk L , A r for liquid argon solution, varies non-linearly with composition. The results imply a saturation effect which occurs when one solvent N 2 molecule is present in the first solvation shell of the excited molecule. It is proposed that this is due to the formation of a N 2 (v = 1) N 2 collision complex.