Very accurate potential energy curve of the ${\rm He}_2^+$ He 2+ ion

Abstract

A very accurate ground-state potential energy curve (PEC) of the He(2)(+) molecule is calculated with 1200 explicitly correlated Gaussian functions with shifted centers in the range between 0.9 and 100 a(0). The calculations include the adiabatic corrections determined for the (3)He(4)He(+), (3)He(2)(+), and (4)He(2)(+) isotopologues. The absolute accuracy of the PEC is better than 0.05 cm(-1) and that of the adiabatic corrections is around 0.01 cm(-1). The depths of the PECs augmented with the adiabatic corrections for the three isotopologues are: 19 956.708 cm(-1) for (4)He(2)(+), 19 957.054 cm(-1) for (3)He(4)He(+), and 19 957.401 cm(-1) for (3)He(2)(+). The rovibrational energies are also determined. For (3)He(4)He(+) the computed rovibrational transitions corresponding to the ν = 1-0 band differ from the experiment by less than 0.005 cm(-1). For the rovibrational transitions corresponding to the ν = 23-22 band the difference is around 0.012 cm(-1). Presently, this represents the best agreement between theory and experiment for He(2)(+).

Radiative association of He+2revisited

“…Our maximum rotational quantum numbers differ from those presented by Stancil (1994) for four vibrational states (for v = 1, 11, 20, and 23 our N max are 55, 35, 13, and 3, respectively). The X 2 Σ + u potential energy curve of Tung et al (2012), our A 2 Σ + g potential energy curve, and our transition dipole moment function connecting these two states also seem to agree very well with the corresponding function plots of Ignjatovic et al (2009) with no visible differences. Cross sections for a spontaneous (T b = 0 K) radiative association are shown graphically in Fig.…”

“…However, the qualitative agreement with these studies is very good. The X 2 Σ + u potential energy curve of Tung et al (2012) supports 409 rotational-vibrational bound states as opposed to 411 states found by Stancil et al (1993). Our maximum rotational quantum numbers differ from those presented by Stancil (1994) for four vibrational states (for v = 1, 11, 20, and 23 our N max are 55, 35, 13, and 3, respectively).…”

“…Using the high-level calculations of Tung et al (2012) for the X 2 Σ + u state as reference, we calculated the potentials of the three lowest 2 Σ + g states on a comparable accuracy level. In Table 1 some data characterizing the three excited states potentials are summarized.…”

“…In the case of potential energy curves U, the interpolation was done with respect to r 2 ( (Tung et al 2012) were exploited as known data points for the interpolation. We calculated ab initio interaction energies for the excited states A 2 Σ + g , C 2 Σ + g , and E 2 Σ + g and the corresponding transition dipole moment values employing the multireference configuration interaction method (combined with a very large electron basis set) as implemented in the quantum chemistry program suite MOLPRO (Werner et al 2010).…”

“…There have been numerous accurate theoretical studies of the X 2 Σ + u ground electronic state of the He + 2 ion, culminating in the highly accurate calculations of its adiabatic potential energy curve by Cencek & Rychlewski (1995) and most recently in calculations of the ground state potential including adiabatic corrections by Tung et al (2012). Theoretical studies on a similar high accuracy level of the excited states are less frequent, which is partly due to the fact that within the adiabatic approximation these states undergo numerous avoided curve crossings.…”