Repopulation of Nitrogen Excited Triplet State Following Laser-Induced Filamentation

Laser-induced filamentation was used to study the dynamics of excited molecular nitrogen decay processes. It is well-known that upper excited nitrogen triplet states can be repopulated at time delays far longer than their fluorescence lifetimes. Examination of the time-resolved emission from several different species indicates that there are two major mechanisms acting to repopulate the N-2((CIIu)-I-3) excited state. The results implicate dissociative electron recombination with the nitrogen cation dimer, N-4(+), and energy pooling between two N-2(A(u)(3 Sigma)(+)) triplet states as the main pathways to repopulate the emissive upper triplet state. The densities of N-2(A(3)Sigma(+)(u)) and free electrons produced during filamentation were measured under atmospheric pressures in nitrogen and estimated to be [N-2(A(3)Sigma(+)(u))](0) = 3 X 10(15) cm(-3) and [e](0) = 3 X 10(13) cm(-3). The methods outlined in this report could find significant utility in measuring the concentration profiles of these important reactive intermediates within laser-induced filaments produced under different conditions.