Radiative lifetime of the $a{}^3{\Sigma }^{+}$ 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 {\it ab initio} methods to evaluate the radiative lifetimes of the six vibrational levels of the $a{}^3{\Sigma }^{+}$ of HeH${}^{+}$. The transition $a{}^3{\Sigma }^{+}\to X{}^1{\Sigma }^{+}$ is spin-forbidden, but acquires intensity through spin-orbit interaction with the singlet and triplet $\Pi$ 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 $a{}^3{\Sigma }^{+}$ and $X{}^1{\Sigma }^{+}$ states are obtained using a B-spline method and compared to previous works. We find that radiative lifetime of the vibrational levels increases strongly with $v$, the lifetime of the $v=0$ state being of 150 s. We also analyze the contributions from discrete and continuum parts of the spectrum. With such a long lifetime, the $a{}^3{\Sigma }^{+}$ state could have astrophysical implications.

9 pages, 5 figures

References in corpus (1)

• Ab initio calculation of H + He${}^{+}$ charge transfer cross sections for plasma physics

Cited by in corpus (4)

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• Determination of photodissociation and radiative association cross sections from the same time-dependent calculation
• Potential energy curves for the interaction of Ag(5s) and Ag(5p) with noble gas atoms