Vibrational Relaxation and Electronic Quenching of the C 3Πu (υ′ = 1) State of Nitrogen

Abstract

A molecular lifetime apparatus was used to study energy transfer processes of the C 3Πu state of nitrogen. Kinetic and luminosity measurements as a function of pressure indicate a cross section σ(3) = 2.5 ± 0.7 Å2 for vibrational relaxation of N2(C 3Πu)υ′=1 by ground-state nitrogen molecules. A useful result of the kinetic analysis is that although the observed lifetime (including quenching) decreases with υ′, vibrational relaxation reduces the gross C state luminescence decay to a single exponential, characteristic of the υ′ = 0 level. Natural radiative lifetimes and electronic quenching cross sections, σ(2), were determined for the υ′ = 0 and υ′ = 1 levels of the C state: υ′ = 0: τ = 40.5 ± 1.3 nsec and σ(2) = 1.98 ± 0.02 Å2; υ′ = 1: τ = 44.4 ± 1.4 nsec and σ(2) = 1.42 ± 0.71 Å2. Estimates of electronic and vibrational deactivation cross sections for the υ′ = 2 level are υ′ = 2: σ(2) = 3.9 ± 0.8 Å2and σ(3) = 1.6 ± 0.4 Å2. The efficiencies for excitation of the υ′ = 0 and υ′ = 1 levels by the secondary electronsproduced by fission fragments are in the ratio 1.0:0.44. It is argued that the C 3Πu(υ′ = 1) state deactivates in two ways through a common N4 intermediate, viz., C 3Πu(υ′ = 1) + X1Σg+(υ′ = 0) ± N4(C2υ)→ lim IB 3Πg(υ″ = ξ) + X 1Σg+(υ″ ≥ 0) → lim IIC 3Πu(υ″ = 0) + X 1Σg+(υ″ = 0) and that the strong vibrational relaxation is accounted for by a nonadiabatic mechanism originally proposed by Nikitin for vibrational relaxation of ground-state NO.