Electron Recombination with Small Molecular Ions

In this thesis I have theoretically studied electron recombination processes with small molecular ions. In these kind of processes resonant states are involved. To calculate the potential energy for these states as a function of internuclear distance, structure calculations and scattering calculations have to be performed. So far I have been studying the ion-pair formation with in electron recombination with H3 . The cross section for this process has been calculated using di erent kind of models, both a time dependent quantum mechanical and a semiclassical. I have also studied the direct process of dissociative recombination of HF+. To calculate the total cross section for this process, we have performed wave packet propagation on thirty resonant states and summed up the individual cross sections for these states. The cross sections for both these processes have a similar appearance to those measured experimentally in the ion storage ring CRYRING in Stockholm. List of papers included in the thesis: Paper I: Ion-pair formation in electron recombination with H 3 Å. Larson, J. Roos and A. E. Orel Phil. Trans. R. Soc. A, 364, 2999 (2006) Paper II: Electron collisions with H 3 : ion-pair formation J. B. Roos, Å. Larson and A. E. Orel (Manuscript, to be submitted to Phys. Rev. A) Paper III: Dissociative recombination of HF J. B. Roos, Å. Larson and A. E. Orel (Manuscript, to be submitted to Phys. Rev. A) i Acknowledgments I would rst like to thank Hans Ågren for given me the opportunity to accompany Åsa Larson, my supervisor, when she moved to the Theoretical Chemistry department in 2006. Åsa Larson and Ann Orel, I really enjoy working with you. Being a mother of two it is extra inspiring to have you as role models. Finally I would like to thank my supporting family and friends. ii Contribution from the author The thesis is based on three theoretical papers, one published and two in manuscript form. In paper I, I was involved in the structure calculations. I performed a diabatization of the calculated adiabatic potential energy surfaces and extrapolated these surfaces to their asymptotic limits. I was also involved in the calculation of the electronic couplings between these surfaces and the extrapolation of these. I also calculated the classical reaction path on the ion-pair potential energy surface. This path I then extracted from all calculated potential surfaces and the achieved curves were used for a semiclassical calculation of the ion-pair reaction cross section. In paper II, we were using MCTDH method to propagate the wave packets. This method requires that the potential surfaces and couplings to be in product form. I have developed a function that has the required form and works well for all the diabatic potentials calculated earlier and tted these to that function. I was also performing the tting of all electronic couplings to appropriate forms. In paper III, I have been performing all the structure calculations and the scattering calculations for the states of singlet symmetry. I have performed the diabatization of the potentials. I have determined the asymptotic limits for the system and extrapolated all potentials and autoionization widths using appropriate methods. Finally I performed wave packet propagation on the resonant states of the system and calculated the cross section for the reaction. I have also written the paper. iii