THE ROLE OF THE METASTABLE POTENTIAL WELL OF $He_{2}^{++}(X^{1}\Sigma_{g}{^{+}})$ IN THE PROCESS $He^{++} + He + e \rightarrow He^{+} + $He
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Date
1978
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Ohio State University
Abstract
The MCSCF potential curve of the $X^{1}\Sigma_{g}{^{+}}$ and $2^{1}\Sigma_{g}{^{+}}$ ground states of $He_{2}^{++}$ have been computed with a near Hartree-Fock limit one-electron basis and a 4-sigma, 2-pi orbital basis. Only diagonal double excitations were necessary in the construction of the MCSCF wavefunction. The intermediate and long range potential for $He{^{+}}(^{2} S) + He{^{+}} (^{2}S)$ is purely Coulombic. However, at short range the two electrons localize between the two nuclei giving rise to a sizable metastable well in an otherwise repulsive curve. The well is 1.3 eV deep, occurs at $Re = 0.71$ \AA, and has a vibrational spacing of about 0.4 eV. This well is capable of supporting at least three vibrational states of ($^{3} He^{4}He)^{++}$ and, thus, should be observable in mass spectrometric detection experiments. These results compare very well with other theoretical calculations. The excited state curve for $He^{++}$ approach to He has a shallow polarization well. The excited state curve never approaches the hump in the ground state curve. The role of these potential curves in the process $He{^{++}} + He + e \rightarrow He^{+} +$ He is discussed. The mechanism \[ \begin{array}{l} He^{++} + He \stackrel{m}{\rightarrow}He_{2}^{++}(2^{1} \Sigma_{g}{^{+}})\\ He_{2}^{++} (2^{1}\Sigma^{+}) \rightarrow He_{2}^{++} (X^{1} \Sigma_{g}{^{+}}) +h\nu\\ He_{2}^{++} (X^{1} \Sigma^{+}_{g}) + e \rightarrow He{^{+}} + He + k.e. \end{array} \] is proposed.
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Author Institution: Science Applications Incorporated