Volume emission rate profiles in the day airglow of the 3371-A emission in the second positive (2 PG) system of N2 have been systematically measured on the Atmosphere Explorer-C satellite. For solar zenith angles (SZA) ranging from 35¿ to 75¿, the volume emission rate maximum varies from 68 to 13 photons/cm3S. A sharp dependence on the neutral atmosphere composition is noted: for SZA=54¿-53¿, &eegr;mnx=60 photons/cm3s for O/N2=0.83 and &eegr;mnx=37 photons/cm3s for O/N2=1.37 at z=170 km. The experimental results are in good agreement with the calculated excitation of the XXXXXXX state of N2 using theoretical photoelectron flux profiles and a diurnal model of th mid-latitude ionospheric F region.