Accurate spectroscopic calculations of the 12 Λ-S and 25 Ω states of the NH radical including the spin-orbit coupling effect

Abstract

Theoretical investigations on the potential energy curves of 12 Λ-S states (X3Σ−, a1Δ, b1Σ+, A3Π, c1Π, 23Π, 21Π, 15Σ−, 23Σ−, 13Δ, 11Σ−, 13Σ+) of NH radical were made for internuclear separation from about 0.6–11Ǻ. These Λ-S states correlate to the first three dissociation channels. Of these 12 Λ-S states, the 21Π, 15Σ−, 13Δ, 11Σ− and 13Σ+ states are repulsive. The c1Π state has one potential barrier. The 23Π and 23Σ− states were found to be bound for the first time. All the PECs were obtained by using CASSCF method followed by the icMRCI approach with Davidson modification. To improve the calculation accuracy, core-valence correlation and scalar relativistic corrections were taken into account. All the 12 Λ-S states split into 25Ω states when the spin-orbit coupling effect was included. The spectroscopic parameters of all the Ω states were determined. To complement the spectroscopic properties of the NH radical, we included the transition properties and presented the allowed transition dipole moments of four transitions as well as the lifetimes of the corresponding vibrational levels. All results were compared with available measurements and other theoretical ones. Excellent agreement between them was found.