Spectroscopy of the Radiation-Induced Intermediates Resulting from Phosphine Irradiation in Inert Matrices: Anionic Species

Phosphine (PH3) is one of the key inorganic molecules resulting from various biogenic compounds in the Earth and planetary atmospheres. The action of ionizing radiation on phosphine molecules may lead to the formation of charged species, the characteristics of which are poorly studied. In this work, vibrational spectra of isolated $${\text{PH}}_{2}^{ - }$$ and PH–• anions stabilized in the X-ray irradiated PH3/Ne and PH3/Ar mixtures at 4.5 K were experimentally obtained and assigned for the first time. The results show that the frequencies of the P–H stretching vibrations in anionic species are red‑shifted in respect to the vibration frequencies of the corresponding neutral molecules or radicals, indicating a weakening of the P−H bonds as a result of electron capture. Based on the analysis of the structure of the PH–• absorption bands in a neon matrix, it was suggested that this anion can result from two different mechanisms: the capture of thermalized electrons by PH…H2 pairs stabilized in the same cage, and the dissociative capture of “hot” electrons by phosphine molecules.