The emission spectrum of helium hydride. V. Characterization of low‐lying Rydberg states (n=2–5)

Spectroscopic properties of the low-lying states of the HeH radical

Four lowest electronic states (X2Σ+, A2Σ+, B2Π and C2Σ+) of the HeH radical are investigated by performing high-precision ab initio calculations. Potential energy curves of HeH are calculated using the internally contracted multireference configuration interaction method in combination with the basis set of aug-cc-pV6Z. To improve the accuracy, additional Rydberg basis functions and the Pople correction are included in the calculations. The spectral parameters are evaluated and compared with literature data. The spin-orbit coupling effect of B2Π is taken into account by using the Breit-Pauli operator. Transition dipole moments between those four electronic states are also derived to obtain their emission spectra and radiative lifetimes. Radiative and predissociation lifetimes of several vibrational levels are also calculated, including the bound-continuum and bound-bound systems. Especially, the predissociation lifetimes are elaborated in detail. The results are in good agreement with the reported ones. Additionally, the emission spectra of bound A2Σ+, B2Π and C2Σ+ states to continuum X2Σ+ state are simulated at different temperatures.