Excitation and decay of N2(B-3 Pi g,v) states in a pulsed discharge: Kinetics of electrons and long-lived species

The vibrational excitation and decay of N-2(B (3)Pi(g)) state has been inve stigated in a N-2 pulsed rf discharge. The effect of the pulsing frequency and the duty cycle on the N-2(B, upsilon = 1-12) vibrational distribution, obtained from the 1PG spectra taken at different times in discharge and aft erglow, has been examined in the N-2 pressure range 2.4 mTorr-1.5 Torr. The measured (B, upsilon) distributions have been analyzed by a steady-state k inetic model taking into account the main excitation processes, like the el ectron impact from N-2(X (1)Sigma(g)(+), upsilon) and N-2(A (3)Sigma(u)(+), upsilon) states, the associative excitation of N-2(X, upsilon) with N-2(A, upsilon), the pooling by N-2(A, upsilon) molecules, the atomic recombinati on of N(S-4), as well as the quenching processes. For the various processes , experimental state-to-state rate coefficients from the literature and/or calculated data sets have been used. Measured N-2(A, upsilon) and electron energy distribution functions, and estimated N-2(X, upsilon) distributions have been used as input data for the model. The model satisfactorily reprod uces almost all the measured distributions. The kinetic analysis evidences that the shape of the (B, upsilon = 1-12) distribution depends on the compe tition between the different processes and in turn on the time variation of both density and the degree of internal excitation of the reaction species with discharge repetition rate, duty cycle, and pressure. In general, in t he discharge the electron impact is always the predominant excitation mecha nism, while the processes involving long-lived species: N-2(A, upsilon) and N-2(X, upsilon) are important in the postdischarge regime. Under condition s of high metastable density, the associative collision processes contribut e to (B, upsilon) excitation in the discharge, and the electron impact proc ess from the A and X states gives a non-negligible contribution to the low upsilon levels in the millisecond time scale afterglow. An analysis of the B quenching is carried out. (C) 1999 American Institute of Physics. [S0021- 9606(99)01106-X].