Dissociative Attachment in Polar and Highly Polar Molecules

Abstract

The behavior of electron scattering by hydrogen halides HX (dipole moment 0.4–1.8 D) has arisen the interest to study the collisions of electrons with highly polar molecules, like the alkali halides MX. New phenomena have been observed in hydrogen halles, stimulating the calculation of electron scattering with polar and highly polar molecules, recently reviewed¹. Concerning the dissociative attachment in hydrogen halides, the most abundant ion is X^–; striking features observed in the X^– formation are the coupling of the dissociation and autodetachment continua^2,3 and the large effect of the initial rovibrational energy of the HX ground state on the absolute cross-section^4–7. The H^– ion (about 1% of X^–) is formed thru 3 dissociative resonant states, with the ${}^2\sum\nolimits_{{\frac{1}{2}}} {}$ and ²Π_3/2 HX^– states correlated to the dissociation asymptote H^–+Br(²P_3/2) and the ²Π_3/2 state correlated to H^–+Br(²P_1/2). Coupling between the ${}^2\sum\nolimits_{{\frac{1}{2}}} {}$ and ²Π_1/2 states has been observed in HBr⁸ and in HCl^9,10. This effect could be attributed to non-adiabatic coupling between these states with the same Ω=1/2 symmetry⁸ and/or to electronic coupling via the non-resonant e-HX continuum¹¹.

Laboratoire associé au C.N.R.S.