Radiative lifetime of the a Σ3+ state of HeH+ from ab initio calculations

Abstract

The first metastable triplet state of HeH(+) was found to be present in ion beam experiments, with its lifetime estimated to be between hundreds of milliseconds and thousand of seconds. In this work, we use ab initio methods to evaluate the radiative lifetimes of the six vibrational levels of the a (3)Σ(+) of HeH(+). The transition a (3)Σ(+)→X (1)Σ(+) is spin-forbidden, but acquires intensity through spin-orbit interaction with the singlet and triplet Π states. Large scale CASSCF/MRCI calculations using an adapted basis set were performed to determine the potential energy curves of the relevant states of HeH(+) as well as the matrix elements of the dipole and spin-orbit operators. The wave functions and energies of the vibrational levels of the a (3)Σ(+) and X (1)Σ(+) states are obtained using a B-spline method and compared to previous works. We find that the radiative lifetime of the vibrational levels increases strongly with v, the lifetime of the v=0 state being 150 s. We also analyze the contributions from discrete and continuum parts of the spectrum. With such a long lifetime, the a (3)Σ(+) state could have astrophysical implications.

Isotope effect in charge-transfer collisions of H with He+

“…Accordingly, it is necessary to compute the potential energy curves (PEC's) of the HeH + molecular ion, as well as the nonadiabatic couplings, in both spin multiplicities. For n = 2, this amounts to a total of 12 states, which have been studied previously [12,13]. We reproduce the potential energy curves of these states in Figs.…”

Photodissociation and Radiative Association of HeH+ in the Metastable Triplet State

“…The potential supports six vibrational states for J = 0, as was reported in Ref. [15]. The ground vibrational state is bound by 664.8 cm −1 while the v = 5 state is bound by less than 2 cm −1 , and there is a total of 51 bound rovibrational states.…”

Potential energy surface and bound states of the NH3–Ar and ND3–Ar complexes

“…52 The energies of the levels were subsequently fitted to the standard expression In order to interpret the spectrum, we first computed the vibrational spectrum obtained from the isotropic potential v 00 (R, ρ e ) using a B-splines method. 53 For each j k level of NH 3 Let us now discuss the results obtained from the full 4D calculations with the anisotropic potential. The band origins of the vibrational states of ortho NH 3 -Ar up to an energy of −25 cm −1 are shown in Fig.…”