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The impact parameter method for electron impact excitation of diatomic molecules has been extended to treat dissociation and to include the effects of vibrational and rotational excitation. The method was found to agree well with previous theoretical calculations of excitation and dissociation cross sections for H2. The agreement with experimental cross sections is poorer but consistant with our understanding of the processes. The method has been applied to electron impact excitation and dissociation of 02, S2, HCl, and HgBr through optically allowed transitions. Vibrational excitation of the molecule can significantly affect the cross sections for these processes, either increasing or decreasing the cross sections by as much as 2 orders of magnitude, whereas, rotational excitation has a much smaller effect on the cross sections.

First principles calculations are reported of high velocity vibrational excitation and relaxation processes in several molecules of importance in plume technology. These involve collisions of atomic oxygen with HF, HC1, CO, water, and carbon dioxide. Cross sections for vibrational excitation and relaxation are reported, along with vibrational relaxation rate constants. The effect of chemical reaction channels in these systems is discussed, and is relatively unimportant except at the highest velocities considered. Translational energies were studied up to 6 eV. (Author)

Single electron capture and ionization cross sections have been calculated for collisions of He(++) with Li over the relative collision velocity range 0.1-10.0 x 10 to the 8th power cm/sec. For low collision velocities (i.e., v = 0.1-0.6 x 10 to the 8th power cm/sec), a molecular approach has been used to determine the electron capture cross section. Ab initio potential energy curves and coupling matrix elements have been computed for the (HeLi)++ system and used in a cross section evaluation based on the perturbed-stationary-state method. For the low velocities, the electron capture reaction He(++) + Li yields He+(3l) + Li(+) is found to dominate the collision process and proceeds with a large cross section, sigma approximately 10 to the minus 15th power sq cm, thus providing the possibility for population inversion and the subsequent emission of Lyman-alpha (304 A) and Lyman-beta (256 A) soft x-ray photons. At the higher velocities (i.e., v=1.4-10.0 x 10 to the 8th power cm/sec), a classical-trajectory Monte-Carlo method has been used to estimate both the electron capture and ionization cross sections. At 2.2 x 10 to the 8th power cm/sec, both cross sections are found to be equal, while one ionization dominates the collision process at higher velocities and electron capture dominates at lower velocities., Prepared in cooperation with SRI International, Menlo Park, CA. Molecular Physics Lab., Rept. no. MP-78-02.