Lifetime of the N2 Vegard–Kaplan System

Abstract

The results of an experiment by Carleton and Oldenberg, designed for the measurement of the relative lifetimes of the ${\mathrm{N}}_2{B}^3{\mathrm{II}}_g$ and $A^3{\Sigma }_u^{+}$ states, have been reanalyzed. The reanalysis was prompted by the assumption, in the original analysis, that the N₂ first positive $\text{(1PG)}$ (1, 0) band could be described as a Hund's case (b) transition in the levels contributing significantly to the emission. The $B^3{\mathrm{II}}_g$ state is in fact intermediate in coupling between Hund's cases (a) and (b), with a rather gradual change from case (a) to case (b) as a function of increasing $J$ . The error in the calculation of the population of the $A^3{\Sigma }_u^{+}\text{(υ\hspace{0.17em}=\hspace{0.17em}0)}$ level from the measurement of self‐absorption in the ${\mathrm{N}}_2\text{1PG}$ (1, 0) band, assuming Hund's case (b) coupling, is significant. An additional error due to neglect of a degeneracy factor (Λ‐type doubling) resulted in a relative lifetime differing by a factor of about 7 from the recalculated value. The lifetimes of the $A^3{\Sigma }_u^{+}\text{(υ\hspace{0.17em}=\hspace{0.17em}0)}$ level, calculated using the $B^3{\mathrm{II}}_g\text{(υ\hspace{0.17em}=\hspace{0.17em}1)}$ lifetime measured by Jeunehomme, are 1.36 sec for the $\text{Σ\hspace{0.17em}=\hspace{0.17em}0}$ , substate and 2.7 sec for the $\text{Σ\hspace{0.17em}=\hspace{0.17em}1}$ , −1 substates, with a probable error of about 20%.