Interstellar Formation of the Elusive Phosphanyloxyphosphane (H ₂ POPH ₂ ) and Phosphanylphosphinous Acid (H ₂ PPHOH) via Nonequilibrium Chemistry: Precursors to the Phosphate Backbone of Nucleotides

The P-O-P moiety plays a central role in inorganic and biological systems and is considered to be a critical precursor to the phosphate backbone of nucleotides. However, the isolation of the simplest prototype, phosphanyloxyphosphane (H₂POPH₂), has remained elusive due to its high susceptibility to hydrolysis. Here, we report the first preparation of phosphanyloxyphosphane and its isomer phosphanylphosphinous acid (H₂PPHOH) in low-temperature phosphine (PH₃)-carbon dioxide (CO₂) ices upon exposure to galactic cosmic ray proxies in the form of energetic electrons. These isomers were isolated and identified in the gas phase using tunable vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry combined with isotopic labeling studies. Our findings not only suggest that the hitherto undetected phosphanyloxyphosphane and phosphanylphosphinous acid can be synthesized in phosphine-rich extraterrestrial ices but also advance our fundamental understanding of the formation of P-O-P and P-P-O linkages via nonequilibrium chemistry under astrophysical conditions.