Multiple differential electron spectra from detachment in collisions of 30–300-keV anions with atoms and molecules

We have measured triple differential momentum distributions for electron detachment in collisions of 30- and 300-keV anions (<a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msup><a:mrow><a:mi mathvariant="normal">C</a:mi></a:mrow><a:mo>−</a:mo></a:msup></a:math> and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi mathvariant="normal">S</c:mi><c:msup><c:mrow><c:mi mathvariant="normal">i</c:mi></c:mrow><c:mo>−</c:mo></c:msup></c:mrow></c:math>) with atoms and molecules (He, Ar, and <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:msub><f:mi mathvariant="normal">N</f:mi><f:mn>2</f:mn></f:msub></f:math>). The entire angular range of the ejected electrons was covered. The binary encounter ring, well known from positive ion-atom collisions, was observed in most cases. In a quasifree-electron scattering model this structure represents elastic scattering of the active electron from the target. However, especially for the slowest projectiles, this model fails to reproduce the angular distributions. In this regime it is probably necessary to use quasimolecular models to describe the collision. Indications for a projectile cusp are observed, implying that excitation-induced dipole moments in the ion projectile may be important.