Knowledge Bank

The MCSCF potential curve of the $X1\Sigma g\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$ and $21\Sigma g\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$ ground states of $He2++$ 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 $He\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}(2S)+He\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}(2S)$ 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 ($\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}He4He)++$ 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 $He\mathrm{<mrow\; data-mjx-texclass="ORD">++</mrow>}+He+e\to He++$ 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.