The excitation of N(2P) by N2(A 3∑+u, v′=0,1)

Abstract

We have studied the electronic energy transfer reaction between N2(A 3∑+u, v′=0,1) and N(4S) in a discharge-flow reactor. Monitoring the decay of the forbidden Vegard–Kaplan emission, N2(A 3∑+u−X 1∑+g ), as a function of time and of atomic nitrogen number density allows determination of the total reaction rate coefficients for removal of vibrational levels 0 and 1 by N(4S). Simultaneously observing the temporal profiles of the Vegard–Kaplan bands and of the forbidden N(2P−4S) line at 346.6 nm allows the branching fraction into atomic nitrogen excitation to be determined. The total quenching rate coefficient for both v′=0 and 1 is (4.0±0.5)×10−11 cm3 molecule−1 s−1 at 300 K. The apparent rate coefficient for exciting N(2P) by N2(A, v′=0) is (19±3)×10−11 cm3 molecule−1 s−1, at 300 K, while that for excitation by N2(A,v=1) is (5±1)×10−11 cm3 molecule−1 s−1. We interpret the large discrepancy between the N(2P) excitation and N2(A) destruction rate coefficients as evidence that the currently accepted value for the N(2P−4S) transition probability is a factor of 4 to 5 too small, or else that our source of N2(A) metastables, energy transfer from metastable argon atoms to molecular nitrogen, is contaminated by the presence of a second nitrogen metastable species with an energy in excess of 3.6 eV.