Synthesis of the hitherto elusive formylphosphine (HCOPH2) in the interstellar medium – a molecule with an exotic phosphorus peptide bond

Abstract

The formylphosphine (HCOPH₂) molecule was detected in the gas phase via isomer selective photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS). Synthesized in carbon monoxide (CO)–phosphine ices (PH₃) exposed to ionizing radiation, the formation mechanism involves an initial phosphorus–hydrogen bond rupture in phosphine yielding the phosphino radical (PH₂) along with atomic hydrogen, addition of the suprathermal hydrogen atom to carbon monoxide leading to the formyl radical (HCO), and recombination of both radicals to formylphosphine (HCOPH₂). This molecule represents the isovalent counterpart of the ubiquitous interstellar formamide (HCONH₂). This study provides a fundamental framework to explore the synthesis and stability of the simplest isovalent counterpart of interstellar formamide (HCONH₂) and suggests that formylphosphine (HCOPH₂) should be detectable in the interstellar medium eventually providing a missing link between phosphorus-bearing complex organic molecules detected in the interstellar medium and on comet 67P/Churyumov–Gerasimenko.