In this paper we report on complementary measurements on ion-pair formation in collisions between K atoms and CH 3 N0 2 molecules. The experiments were performed in a c.m. energy range from 20 up to 300 eV. Double differential cross sections were obtained by measuring the K + ion yield as a function of the scatter angle and as a function of the post-collision laboratory energy. On the other hand, relative total partial cross sections for the formation of CH 3 N0 2 -, N0 2 -, and 0 -were measured in the same energy range. The experimental results lead to the conclusion that in this energy range electron transfer takes place to three ionic states ofCH 3 NO; , a dominantly repulsive 2AI state and two 2EI states with relatively deep potential wells. 166 J. Chem. Phys. 95 (1).1

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Dissociative ion-pair formation in collisions of fast potassium atoms with benzene and fluorobenzeneThe reaction K + ACl,----K+ + (A -Cl.r· with A = Sn and C was examined as a function of the collision energy from threshold up to about 40 eV in the c.m. system. Total cross sections of the mass-selected negative ions and doubly differential cross sections (energy and angle) of the K+ ions have been determined. Electron affinities, bond energies, and electronic excitation were calculated from the appearance potentials. In addition, the total cross sections for SnCI. were measured and are contrasted with the earlier results of CCI, from Dispert and Lacmann. Although both parent molecules have the same electron affinity within their error limits (2.2 eV for SnCI. and 2.0 eV for CCI.) and the same dissociation energy for the negative ions of 1.4±0.2 eV, the product ion yields differ drastically. The main negative ion yield in K + SnCI. results from SnCl.formation (over 80%). Its lowest dissociation channel leads to SnCI; formation, while Cl-ions are the main ions produced (90%) from CCl" with only 7% leading to CCl; + CI formation at higher energies. These results support orbital energy considerations of electron addition to SnCl, and CCI. as applied to the results of reactive colJisions of these molecules. The electron affinity and an electronically excited state of SnCl 3 have been also determined. Morse potentials of CCI. and SnCl. were fitted to the experimental results of energy loss measurements from this work. The vertical electron affinities thus derived are 1.15 eV for SnCI. and -1.0 eV for CCl •.

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