Spectral features of photoionization of ground and excited levels of P I

Spectral features of photoionization of various fine structure levels of P I, (P I + hν → P II + e), are reported. These include characteristic features of Rydberg and Seaton resonances, equivalent electron levels, low and high lying excited levels, and their impact on the background cross sections, and effects of fine structure couplings. Calculations were carried out in the relativistic Breit–Pauli R-matrix method with close-coupling (CC) approximation that generates the resonances naturally. The CC wavefunction expansion for P I includes ground and 27 excited levels of the core ion P II with orbitals of n = 3 and n = 4 complexes and 87 configurations of P I for bound channel contributions. Photoionization cross sections (σ PI ) with detailed resonances are presented for all 543 fine structure levels of P I found with 1/2 ≤ J ≤ 15/2 of even and odd parities and n ≤ 10 and l ≤ 9. The autoionizing resonances are delineated with a fine energy mesh to observe the fine structure effects. The ground level shows typical feature of smoothly decreasing σ PI with increasing energy. However, a compressed set of narrow resonances is found to form by the coupling of channels in fine structure at the ionization threshold of photoionization for the ground and many excited levels. These resonances and strong Rydberg resonances in the low energy region are found in photoionization spectra of the five equivalent electron levels of P I. Low lying excited levels show presence of strong Rydberg resonances and many with enhanced background cross section. Prominent Seaton resonances due to photo-excitation-of-core, often with enhanced background, are seen in photoionization of single valence electron high lying excited levels. Partial cross sections of the ground level with various core ion states are also presented. The present results should provide high-accuracy parameters of various model applications, such as, for exoplanetary atmosphere spectroscopy.