Fast nitrogen atoms from dissociative excitation of N-2 by electron impact

The Doppler profiles of one of the fine structure lines of the N I (1200 Angstrom) g S-4(0)-P-4 multiplet and of the N II (1085 Angstrom) g P-3(0)-D-3 multiplet have been measured. Excitation of the multiplets is produced by electron impact dissociative excitation of N-2. The experimental line profiles are evaluated by fast Fourier transform (FFT) techniques and analysis of the profiles yields the kinetic energy distribution of fragments. The full width at half maximum (FWHM) of N I (1200 Angstrom) increases from 27 +/- 6 m Angstrom at 30 eV to 37 +/- 4 m Angstrom at 100 eV as the emission cross section of the dissociative ionization excitation process becomes more important relative to the dissociative excitation process. The FWHM of the N II (1085 Angstrom) line is 36 +/- 4 m Angstrom at 100 eV. For each multiplet the kinetic energy distribution function of each of the two fragment N atoms (ions) is much broader than thermal with a mean energy above 1.0 eV. The dissociation process with the largest cross section is predissociation and predominantly produces N atoms with kinetic energy distributions having mean energies above 0.5 eV. Dissociative processes can lead to a substantial escape flux of N I atoms from the satellites, Titan and Triton of the outer planets.