New measurements by ground-based spectroscopy of the N2 Vegard-Kaplan system have given values for the v' progression intensities from v'=0 to &ngr;'=3 and upper limits to the values from v'=4 to v'=6. These are combined with other recent measurements of the N2 1P system and theoretical estimates of direct electron impact excitation to the A3&Sgr; state to yield estimates of the rate coefficient for quenching of the A3&Sgr; state by O and the variation of this coefficient with v'. For the v'=0 level a rate coefficient of 7.5¿5.0¿10-11 cm3 s-1 is found to be consistent with reasonable assumptions as to atmospheric composition and auroral luminosity profile. It is concluded that this coefficient must double in value in the range 2<v'<5.