We present the results of large-scale CCSD(T) calculations on the potential energy curves for the ground states of LiHg, NaHg, and KHg. In these calculations, the Hg20+ core is simulated by a pseudopotential which has been adjusted to reproduce experimental excitation and ionization energies of the Hg atom at the coupled-cluster level. Moreover, we apply a weighted multiproperty fitting procedure to determine reliable potentials for LiHg, NaHg, and KHg which reproduce the available experimental results. In the case of LiHg, this best-fit potential is based solely on experimental data and its agreement with our calculated potential supports our computational procedure. For NaHg and KHg the experimental data had to be complemented by theoretical results in order to fix a best-fit potential. Our potentials and those proposed previously are evaluated by comparing calculated scattering cross sections and vibrational energy levels with the available experimental data.
A complete ab initio treatment is applied to the autoionization process in the He*(2s 3S)+Li(2s 2S) collisional complex. Feshbach projection based on orbital occupancy, implemented in a multireference configuration interaction (MRCI) code, defines the resonance state and provides the entrance channel potential curve as well as all pertinent information on the resonance–continuum coupling. The l-dependent coupling elements in local approximation are obtained by projecting a compact one-electron function, named Penning molecular orbital (PMO), onto the wave function of the ejected electron with proper energy. The continuum wave function is obtained by coupled channel calculations in the static-exchange approximation. A converged set of seven complex coupling matrix elements, used in the nuclear dynamics calculation based on a complex Numerov algorithm, fully describes the electron angular momentum transfer. The calculated angle-dependent spectra, as well as the total, angle-, and energy-integrated ionization cross sections agree well with available experimental data.
Using a crossed-beams set-up, we have studied the electron energy spectra due to Penning and associative ionization in thermal energy collisions of stateselected metastable Ar * 4s 3 P 2 , 3 P 0 and Kr * 5s 3 P 0 atoms with ground-state Hg atoms at an electron energy resolution of 30 meV. In all three cases the energy spectra exhibit a prominent peak located close to the energy difference between the metastable excitation energies and the Hg ionization energy; they show a sharp drop to lower and an extended tail towards higher electron energy with shapes which differ for the three systems. The energy-integrated ionization cross section for Ar * 3 P 0 exceeds that for Ar * 3 P 2 by about 30%. Excitation transfer to autoionizing Hg * * states, resulting in a sharp additional structure, is only observed-as a weak channel-in Ar * 3 P 0 + Hg collisions. For the three investigated systems calculations of the electron energy spectra have been carried out within the local optical potential approximation. As input we use ab initio potential curves for the ionic exit channels as well as for the complex entrance channel potentials. Using these potentials (involving a scaled width for Kr * + Hg), impressive agreement with the experimental electron spectra is observed. In contrast, earlier empirical model potentials for the entrance channel are found to be inadequate. The calculated ionization rate coefficients at T = 300 K amount to (3.72, 5.26) × 10 −10 cm 3 s −1 for Ar * 3 P 2 , 3 P 0 + Hg, respectively.
Multireference configuration interaction (MRCI) calculations have been performed for the Ar*(4s3P2,0) + Hg collision complex. Feshbach projection based on orbital occupancy defines the entrance channel resonance states and provides their potential energy curves as well as resonance-continuum coupling matrix elements, which are turned into an autoionization width function by Stieltjes imaging. Coupled cluster calculations with singles, doubles, and pertubative triples [CCSD(T)] give the exit channel potential of ArHg+. The Hg20+ core is treated by a scalar-relativistic effective core potential, reparametrized to reproduce experimental excitation and ionization energies. Spin-orbit interaction is included for the Ar* open 3p shell. The nuclear motion is treated within the local complex potential approximation. Ionization occurs for 85% (3P0) and 98% (3P2) of the symmetry allowed close collisions. Calculated ionization cross sections show good agreement with experimental data. The difference potential of the collision complex is remarkably flat down to internuclear separations of 8a0 and leads to very sharp peaks in theoretical electron energy spectra for single collision energies. After accounting for the experimental energy distribution and the resolution function of the spectrometer, a very satisfying agreement with experimental electron energy spectra is found, including subtle differences due to spin-orbit coupling. Theoretical input appears indispensable for an analysis of the measured data in terms of potential energy curves and autoionization width functions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.