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 N2 B 3IIg and A 3Σu+ states, have been reanalyzed. The reanalysis was prompted by the assumption, in the original analysis, that the N2 first positive (1PG) (1, 0) band could be described as a Hund's case (b) transition in the levels contributing significantly to the emission. The B 3IIg 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 3Σu+ (υ = 0) level from the measurement of self-absorption in the N2 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 3Σu+ (υ = 0) level, calculated using the B 3IIg (υ = 1) lifetime measured by Jeunehomme, are 1.36 sec for the Σ = 0, substate and 2.7 sec for the Σ = 1, −1 substates, with a probable error of about 20%.