Lifetime of the Lowest Excited Level of N2

Abstract

We have measured the probability of transition of the forbidden Vegard—Kaplan system (A3Σ—X1Σ) in N2, working from the definition of this probability as the ratio of number of photons emitted per second to number of excited molecules, both measured in the same discharge. We measure the absolute intensity of the 0,6 Vegard—Kaplan band as emitted from the discharge. Under identical conditions we find the population of molecules in the A3Σ level by measuring the strength of absorption of the 1,0 first positive band. By calculation we relate the observed loss (which is a sum of absorption by all rotational levels) to the absolute population of the excited level, in terms of the probability of transition of the first positive system. Our measurements of absorption and emission give a value of (1.6±0.4) × 106 for the ratio of the transition probability of the first positive system to that of the Vegard—Kaplan system. From recent shock-tube measurements of the former transition probability we obtain a value of 2.0(±0.9) sec for the lifetime of the A3Σ state of N2.