Dissociative recombination and dissociative excitation ofHeH+4: Absolute cross sections and mechanisms

Absolute cross sections have been determined for the dissociative recombination and dissociative excitation of ${}_{}{}^4{}_{}{}^{}\mathrm{HeH}_{}^{+}{}_{}{}^{}$ for electron energies below 40 eV. The dissociative recombination cross section is in semiquantitative agreement with recent theoretical results by Sarpal, Tennyson, and Morgan [J. Phys. B 27, 5943 (1994)] and Guberman [Phys. Rev. A 49, R4277 (1994); in XIXth International Conference on the Physics of Electronic and Atomic Collisions, Whistler, Canada, AIP Conf. Proc. No. 360, edited by L. J. Dube, J. B. A. Mitchell, J. W. McConkey, and C. E. Brion (AIP, New York, 1995), p. 307]. The calculated resonant structure below a collision energy of 1 eV was not fully reproduced by the experiment. The quantum states of the dissociative recombination products at 0 eV collision energy have been determined; ground-state helium and excited hydrogen atoms (n=2) are dominantly formed, in agreement with recent predictions by Guberman. The dissociative excitation has an onset around 10 eV and follows the shape of the dissociative recombination cross section, illustrating that both processes start with the formation of doubly excited neutral states that lie in the ionization continuum as well as in the dissociation continuum. The dissociative excitation cross section is in quite good agreement with recent calculations by Orel and Kulander. © 1996 The American Physical Society.