Polarization and collision velocity dependence of associative ionization in cold Na(3p)-Na(3p) collisions

Abstract

Abstract.We studied the polarization dependence of the associative ionization (AI) process Na(3p)+Na(3p) Na] at collision velocities between 100 and 700 m/s (5 and 200 K), using linearly and circularly polarized light for the excitation. We found that the polarization dependence varies strongly in the collision velocity range under study. At the high end of our scale preparation of both collision partners in the I m~l = 1/2 substates yields the highest AI-rate, but at low velocities this ceases being so: the polarization dependence becomes less pronounced and at the low end of our scale the preparation Irnjll, tmj21 = 3/2, 1/2 is most effective. All cross sections increase strongly at lower velocities. Combined with previous work this maps the detailed polarization dependence from 100-2400 m/s (5-2500 K). From these total results it is concluded that at collision velocities > 500 m/s mainly one molecular potential curve leads to AI, but that this changes considerably at lower collision velocities. The findings are compared with recent theoretical results by GeRman, and we find large discrepancies.

Diabatic representation for the excited states of the Na2 molecule: application to the associative ionization reaction between two excited sodium atoms

“…This value is in reasonable agreement with the experimental value which is around 1-4 ~k 2 [t- 3,23]. Moreover, out of the two curves F2(R ) and F3(R), the lowest one is more likely to be populated from two a3p orbitals, while the upper one contains a larger contribution of the (ng 3 p) (~ 3 p) configuration.…”

“…Besides, our calculations show that the variation of the cross section as a function of the collision energy Er is different in the case of molecular autoionization via a 3Z,+ or via a lAg state [24]. The latest ionization channel being populated from two n atomic orbitals, this could lead to a modification of the polarization dependence of the cross-section when the collision energy is varied [23,24].…”

Doubly-excited states for the Na2 molecule: application to the dynamics of the associative ionization reaction

“…The inclusion tot ~ / of the possibility of flux loss at the long-range pseudocrossings lowers O'to tAI by about 40%. This latter result is still about two times higher than the experimental cross section o-is o of Meijer [4]: however the author presents his absolute measurements with a factor 2 uncertainty. However, most of the experiments are performed with polarized light, inducing an initial preparation I e) of the adiabatic states strongly differing from (13).…”

“…E) values defined in (13) and two choices for Wk(E ) factors is drawn in Fig. 9 and compared with the isotropic experimental cross section ai~ o of Meijer [4]. If the W k (E) factors are chosen equal to unity (sudden approximation, as assumed in paper II), the various cross sections aAI(E) are 237 nearly constant above 20 meV.…”

“…10, and can be compared with the modulation of the experimental ion signal (see Table 2) [4,22]. When the sudden approximation is assumed (Fig.…”