ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The formation of negative ions by electron attachment in collisions of He atoms in the well-defined low-Rydberg state (n=14)1P with SF6 is studied as a function of the relative velocity of the reactants in a crossed-beam experiment at thermal energies. The data show that the cross section does not follow the behavior predicted by the free electron model; it presents a maximum and then decreases at low kinetic energy, thus providing a direct observation of the postattachment Coulomb interaction of the He+ and SF−6 product ions. It is assumed that, at low kinetic energy, rovibrational energy of SF−6 and SF6 which coexist inside a temporary collision complex (He+SF6)−, is transferred into translational energy of the collision products, allowing SF−6 and He+ to escape from the collision complex with reduced vibrational energy in SF−6 and increased kinetic energy of He+. Both can thus be detected even when the ion pair He+–SF−6 is expected to stay bound. This explains qualitatively the nonzero value of the cross section in this low kinetic energy range. At high kinetic energy, transfer of translational energy into rovibrational energy is assumed to occur inside the collision complex, leading to SF−6 ions with increased vibrational energy and thus shorter lifetime against autodetachment. This explains qualitatively the steeper than 1/vr decrease of the cross section in this high kinetic energy range.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.462823
