No abstract
We describe a general procedure for applying the complex Kohn variational method to the calculation of molecular photoionization cross sections and asymmetry parameters. In this initial application of the method, we examine the effects of interchannel coupling and ground state correlation on the X 2Σ+(5σ−1), A 2Π(1π−1), and B 2Σ+(4σ−1) partial photoionization cross sections and asymmetry parameters for the CO molecule. We find that the dominant effect of interchannel coupling is to remove a spurious π→π* resonance feature from the continuum that appears at the frozen-core Hartree–Fock level. We also find that it appears to be important to combine the effects of final channel coupling with a correlated initial target state to achieve quantitatively correct cross sections.
A recently reported peak near 9.5 eV in the cross section for electron impact dissociative recombination of vibrationally cold Ha"*" is due to four H3 resonance states. Using a complex Kohn, electron scattering variational method to obtain resonance energies and widths and a time-dependent wave packet calculation of the dissociation dynamics in the presence of autoionization, we obtain excellent agreement with the position, shape, and magnitude of the reported feature. Vibrational excitation of H3"*" is a dominant competing channel due to a high probability of autoionization during dissociation.PACS numbers: 34.80.Kw Dissociative recombination (DR) of small molecular ions plays a significant role in the kinetics of low temperature plasmas. In this process an incident electron is captured by the ion into an excited electronic state of the neutral, causing the eventual dissociation of the molecule. Dissociation is highly likely because, following the capture, the internal energy is very high, approximately equal to the ionization potential of the molecular ground state plus the incident electron energy. The dissociation can be direct if the neutral state is itself dissociative or indirect if predissociation of a bound intermediate occurs.Modeling the kinetics of low temperature plasmas requires not only the knowledge of the DR rates but also the final product state distributions. Because of the very high internal energies involved, many molecular potential energy surfaces can play a role in the dissociation dynamics so that calculations of DR have been restricted almost exclusively to diatomics, or to triatomics treated with one-dimensional nuclear dynamics [1]. Here we report calculations of the total DR cross section through direct, resonant channels including the 2 nuclear degrees of freedom necessary to represent the dissociation properly.Because of the difficulty of producing the ions in well defined initial vibrational-rotational states, most studies of DR have provided only rates for thermal, or hotter, internal state distributions. Recently measurements of the cross section for DR of the ground vibrational state of H3"*" for incident electron energies from near threshold to almost 30 eV have been obtained using a storage ring [2]. In these experiments Larsson et al. observed a pronounced resonant enhancement in the cross section centered near 9.5 eV with a width of several volts. It is the purpose of this Letter to discuss the resonance states of H3 which cause this enhancement and to present cross sections for this component of the DR.In earlier studies [3] both neutral (H4-H2 or H + H H-H) and ion-pair (H~ + H2'*') fragment channels were found to be produced in the DR of H3"*". Previous electronic structure calculations of the core-excited or doubly excited states of the H3 molecule predicted the existence of a resonant state within this region [4,5], This particular state dissociates diabatically to the ion-pair channel but only after crossing an entire Rydberg series of excited states. As pointed out in...
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