ROLE OF POTENTIAL STRUCTURE IN NONADIABATIC COLLISIONS WITH APPLICATIONS TO HE-]HE++NE(2P(5)3S) AND NA+I-]NA++I-(+NE(2P(6))

The first-order functional-sensitivity densities deltasigma12(E)/delta V(ij)(R) from close-coupling calculations are used for a quantitative probe of the role of structure in crossing diabatic curves used to mod el nonadiabatic collisions. Application to the excitation of Ne by He shows a region of significance for deltasigma12(E)/deltaV12 (R) as a prominent Gaussian-like profile around the crossing point (R) in acco rd with the delta(R-R) idealization of the Landau-Zener-Stueckelberg (LZS) theory. Similarly, the densities deltasigma12(E)/deltaV11(R) and deltasigma12(E)/deltaV22(R) mimic ddelta(R-R)/dR-type behavior with one being the negative of the other in the neighborhood of R, in qual itative agreement with the LZS theory. However, all three sensitivity profiles identify a much broader area of importance for the curves tha n the loosely defined avoided-crossing region. Also, although the sens itivities themselves decrease with increasing energy, the domain of im portance of the curves increases. Examination of the functional-sensit ivity densities deltasigma12(E)/deltaV(ij)(R) for the chemi-ionization collision Na + I --> Na+ + I- reveals regions of potential-function i mportance very different from that predicted by the LZS theory. The ch emi-ionization cross section is about ten times more sensitive to the ionic curve than the covalent curve. Also, the domain of sensitivity o f the ionic curve is larger compared to that of the covalent curve. Th e density deltasigma12(E)/deltaV12(R) for chemi-ionization shows that the area of maximum potential significance is not at the crossing poin t itself but the regions bracketing it on both sides. Also, the domina nt sign dependence of the coupling sensitivity is unexpectedly negativ e. The results offer other observations about the domain of validity o f the intuitive pictures rooted in the LZS theory. The significance of these results to the inversion of inelastic cross-section data is bri efly discussed.