Recent accurate calculations by Magnier et al. (1994) have demonstrated that for some symmetries the long-range excited adiabatic potential curves of the Na2 molecule display many avoided crossings, some of them being due to competition between ionic and covalent dissociation. We have used those molecular data to estimate cross sections for the energy pooling reaction: Na(3p)+Na(3p) to Na(3s)+Na(5s, 4d, 4f) in the framework of a semiclassical multicrossing Landau-Zener model. All the pseudocrossings of the adiabatic potential curves from the Na(3s)+Na(4p) up to the Na(3s)+Na(4f) dissociation limit have been considered. At thermal collision energy (T approximately=500 K) cross sections are in good agreement with available experimental data. At lower collision energy (T approximately=200 K), we show that a 1 Sigma g+ and a 3 Sigma u+ channel correlated to Na(3s)+Na(5s) dissociation limit become dominant. This illustrates the crucial role of long range crossings in the dynamics of collisions between excited sodium atoms at very low energies.
The cross sections for vibrational and rotational excitation of H2, Li2, Na2 and K2 by slow electrons are calculated in the adiabatic approximation using a zero range potential model to obtain the amplitude of electron scattering for a 'frozen' molecule. The advantage of the zero range potential model is the possibility of taking into account explicitly the effect of multiple scattering. The results are compared with the available experimental data and other calculations.
Cross sections sigma (m1m2)nl for the energy pooling processes in the collision between two excited sodium atoms are calculated for the case when the partners are prepared in the 3p-excited states with the definite orbital momentum projections m1 and m2. As a result of the process one of the colliding atoms comes to the ground state and the other partner is excited to nl state with nl=5s, 4d, 4f. The collision velocity is equal to or higher than thermal. The Landau-Zener-locking model (LZ-locking) is developed: the sudden change of the type of the coupling between the electron orbital momentum and the internuclear axis (the locking approximation) is combined with the multicrossing Landau-Zener model. The validity of the LZ-locking model is analysed. The results show strong cross section dependence on the initial quantum numbers m1 and m2, especially in the 5s channel.
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