Theoretical Investigations of Electronic Structures and Spectroscopic Properties of the Diatomic Sodium Phosphide Cation

This study employs high-level <i>ab initio</i> calculation methods to explore the structural, electronic, and spectroscopic properties of the previously uncharacterized diatomic cation NaP⁺. Detailed investigations focus on the manifold of low-lying Λ-S electronic states correlated with both Na⁺ + P and Na + P⁺ dissociation limits. The spin-orbit coupling effects are systematically evaluated, revealing the splitting of these states into distinct Ω components. High-accuracy potential energy curves, spectroscopic constants, and vibrational energy levels are derived using the icMRCI + Q approach with extended basis sets. Besides, transition properties, including Einstein coefficients and radiative lifetimes, are also explored, which are expected to aid spectral observations and interpretations. The radiative association processes for the two spin-allowed quartet-quartet bands are investigated. The temperature-dependent cross sections and photodissociation rates for the two transition bands display comparable characteristics. A comparative evaluation with computational results for neutral NaP confirms the reliability of predicted parameters of the cation studied. In addition, the single photoionization process from the neutral species to the cationic one is simulated. The information derived in this work provides foundational insights into the electronic behavior of NaP⁺, offering guidance for future experimental and theoretical studies on this species.