ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
Formation of anions induced by collisions of low energy electrons (0–14 eV) with the perfluorinated compounds CF4, C2F6, C2F4, and C6F6 is studied (a) in the gas phase under collision-free conditions in a beam experiment, and (b) in the condensed phase where the electron beam interacts with the molecules deposited under ultrahigh vacuum conditions in definite amounts on a cold (20 K) metallic substrate. In the gas phase different fragment anions [F−, (M–F)−, CF−3] are formed via dissociative attachment (DA). From condensed molecules, desorption of anions is virtually restricted to F−. This can be explained by the polarization interaction of the excess charge and the desorption kinematics preferring desorption of light fragment ions. Below 10 eV F− desorption is induced by DA at or near the surface while above 10 eV a nonresonant signal from dipolar dissociation is observed. The present results indicate that the desorption cross section is essentially controlled by the amount of translational energy released to F− in the dissociation of the precursor anion (M−). In CF4 the precursor ion CF−4 is assigned as the T2 shape resonance with its pronounced σCF* antibonding nature. This results in F− with high kinetic energy release, and, consequently, a high desorption cross section. In C2F6 the decomposition of the transitory anion is less direct resulting in a comparatively low desorption yield. In C2F4 and C6F6, on the other hand, electron capture proceeds via the π* system associated with indirect (statistical) decomposition processes. This results in a very low desorption cross section for both compounds. © 1995 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.469764
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