Theoretical ab intio calculations for different symmetry groups of N 2 molecular dimer are performed. It is proved that the potential energy curves of N 2 molecular dimer with D 2h symmetry group have an excimer like a 1B 2g→a 1B 3u transition. The theoretical emission spectra for a 1B 2g→a 1B 3u transition is calculated. The experimentally observed spectra for N 2 molecular dimer is found to be in good agreement with theoretical calculations. The gain coefficient of N 2 molecular dimer at 336.21 nm is estimated. The gain coefficient is measured with amplified spontaneous emission method, experimental results correspond to the estimation in the range of error. In the end the output laser power is estimated.