Collision Strengths and Line Ratios for PII as a Biosignature in Exoplanets

Being the ``backbone'' element of DNA, Phosphorus is a key element in the search for life in the Universe. To aid in the future search for Phosphorus in star-forming regions and thereby in exoplanets, we have constructed a line ratios emission model for PII. This low ionization state is likely to exist in gaseous nebulae with stellar formation and in exoplanetary atmospheres if those atmospheres contain any significant amount of P. There are also 3 primary lines among the fine-structure 3s²3p² transitions in the PII emission spectrum that we are particularly interested in: ³P₂→³P₀ at 21 μm, ³P₂→³P₁ at 33 μm, and ³P₁→³P₀ at 60 μm. Collision strengths for these transitions have been newly calculated and compared the results of Tayal (2004). This level of ionization and especially useful lines make this specific ion especially useful in the search for DNA-based life in the universe. Our results have been found and verified against each other using two versions of the code SPECTRA: The original Fortran version, which has proven accurate and reliable, and a new, modernized C++ version that incorporates the process of electron-ion recombination in its calculations, further improving the code’s accuracy.