Excellent Ultracold Molecular Candidates From Group VA Hydrides: Whether Do Nearby Electronic States Interfere?

By means of highly accurate ab initio calculations, we identify two excellent ultracold molecular candidates from group VA hydrides. We find that NH and PH are suitable for the production of ultracold molecules, and the feasibility and advantage of two laser cooling schemes are demonstrated, which involve different spin-orbit states ( [Formula: see text] and [Formula: see text] ). The internally contracted multireference configuration interaction method is applied in calculations of the six low-lying Λ-S states of NH and PH with the spin-orbit coupling effects included, and excellent agreement is achieved between the computed and experimental spectroscopic data. We find that the locations of crossing point between the [Formula: see text] and [Formula: see text] states of NH and PH are higher than the corresponding v′ = 2 vibrational levels of the [Formula: see text] state indicating that the crossings with higher electronic states would not affect laser cooling. Meanwhile, the extremely small vibrational branching loss ratios of the [Formula: see text] → [Formula: see text] transition for NH and PH (NH: 1.81 × 10(–8); PH: 1.08 × 10(–6)) indicate that the [Formula: see text] intermediate electronic state will not interfere with the laser cooling. Consequently, we construct feasible laser-cooling schemes for NH and PH using three lasers based on the [Formula: see text] → [Formula: see text] transition, which feature highly diagonal vibrational branching ratio [Formula: see text] (NH: 0.9952; PH: 0.9977), the large number of scattered photons (NH: 1.04×10(5); PH: 8.32×10(6)) and very short radiative lifetimes (NH: 474 ns; PH: 526 ns). Our work suggests that feasible laser-cooling schemes could be established for a molecular system with extra electronic states close to those chosen for laser-cooling.