Accurate potential energy curves and spectroscopic properties of the X 3 Σ − , a 1 Δ, b 1 Σ + , and A 3 Π electronic states of the PH molecule

Abstract The present work describes a high-level theoretical study of the PH molecule, focusing on its X 3 Σ − , a 1 Δ, b 1 Σ + , and A 3 Π electronic states. We employed the full valence complete-active-space self-consistent field (CASSCF) wave function as the basis to perform ab initio electronic structure computations, which were conducted at the multireference configuration interaction level with the Davidson correction (MRCI(Q)) and the aug-cc-pV X Z ( X = T, Q, 5, 6) basis sets. After that, we extrapolated these ab initio energies to the complete basis set (CBS) limit to acquire higher-accuracy energies. The neural network (NN) approach was subsequently employed to reconstruct the potential energy curves (PECs), as well as to ultimately derive analytical potential energy functions (APEFs). Spectroscopic constants extracted from the APEFs show excellent agreement with available measurements and computations. Then a complete set of vibrational levels and their classical turning points, along with inertial rotation constants and six centrifugal distortion constants are obtained by numerically solving the nuclear Schrödinger equation.