  In light of the recent discovery of ArH+ in the Crab nebula, it is shown
through high-level quantum chemical comptuations that the global minima on the
Ar+/Ne+ + H2 potential energy surfaces are ArH2+ and NeH2+. Hence, ArH2+ may be
a necessary intermediate in the Ar+ + H2 -> ArH+ + H formation reaction
proposed in the same work where ArH+ is first reported in the Crab nebula.
ArH2+ is also probably an intermediate in the alternative Ar + H+2 -> ArH+ + H
reaction. Additionally, it is shown that Ne+ + H2 -> NeH+2 will subsequently
most likely yield Ne + H+2 and not NeH+ + H offering a possible rationale as to
the absence of NeH+ in spectra obtained from the interstellar medium (ISM).
Following from this, spectroscopic data (both rotational and vibrational) are
provided for NeH2+ and ArH2+ through the use of highly-accurate quantum
chemical quartic and cubic force fields. All possible isotopologues are also
included for 20Ne, 22Ne, 36Ar, 38Ar, 40Ar, 1H, and D. The dipole moments for
these systems are quite large at 5.61 D for NeH2+ and 4.37 D for ArH2+. The
spectroscopic constants provided will aid in the potential detection of these
open-shell noble gas dihydride cations in the ISM.
