|Abstract:||Absolute time-resolved populations of nitrogen molecules in a metastable excited electronic state, N$_2(A^3\Sigma_u^+$), generated in a repetitive ns pulse discharge in reacting gas mixtures, have been measured by Tunable Diode Laser Spectroscopy (TDLAS). N$_2(A^3\Sigma_u^+$,v=0-1) population measurements are made in CO$_2$-N$_2$, CH$_4$-N$_2$, CH$_4$-CO$_2$-N$_2$, and C$_2$H$_4$-N$_2$ mixtures at a pressure of 150 Torr. The mixtures are excited in a diffuse plasma generated by a repetitively pulsed, double dielectric barrier, ns discharge across a 6 mm gap in a plane-to-plane geometry. The data are taken during the discharge bursts up to several tens of pulses long. The results show that the N$_2(A^3\Sigma_u^+$) number density generated in the discharge, both by electron impact and by the cascade quenching of the higher energy excited electronic states, are significantly affected by the mixture components. In CO$_2$-N$_2$ mixtures, the effect on N$_2(A^3\Sigma_u^+$,v) populations is relatively minor, due to the relatively slow quenching rate. In CH$_4$-N$_2$ mixtures, the dominant effect is due to the vibrational energy transfer to methane, resulting in a rapid vibrational relaxation of N$_2(A^3\Sigma_u^+$,v=1 $\rightarrow$ v=0). In CH$_4$-CO$_2$-N$_2$ mixtures, N$_2(A^3\Sigma_u^+$) quenching is also affected by the species generated in the plasma. The results are compared with kinetic modeling predictions, identifying the mechanisms of N$_2(A^3\Sigma_u^+$) generation and decay during the discharge pulses and in the afterglow. The results demonstrate that high-pressure, high repetition rate, volume-scalable ns pulse discharges can be used for efficient generation of atomic and radical species for plasma chemical and plasma catalysis syntheses. N$_2(A^3\Sigma_u^+$) measurements and kinetic modeling analysis can be used to quantify the amount of reactive species generated in the plasma.