Phosphine Reactivity and Its Implications for Pyrolysis Experiments and Astrochemistry

Area of Science:

• Astrochemistry
• Chemical Kinetics
• Theoretical Chemistry

Background:

• Phosphorus-bearing molecules are vital for life and abundant in space.
• The chemical pathways of these molecules, particularly phosphine (PH3), are not well understood.
• Understanding PH3 chemistry is crucial for interstellar medium (ISM) studies.

Purpose of the Study:

• Investigate phosphine (PH3) decomposition and formation pathways.
• Calculate thermodynamic and rate coefficients for key reactions.
• Assess the stability and formation mechanisms of PH3 in interstellar conditions.

Main Methods:

• Utilized high-level electronic structure calculations (CCSD(T)/6-311G(3df,3pd)//ωB97xD/6-311G(3df,3pd)).
• Employed RRKM and semiclassical transition-state theory (SCTST) for rate coefficient calculations.
• Studied thermal dissociation, PO(2Π), PN(1Σ+), and H2O+ reactions over 50-2000 K.

Main Results:

• PH3 is thermally stable below 100 K.
• PH3 can be readily formed via reactions involving PH(3Σ-), PO(2Π), and PN(1Σ+).
• PH3 decomposes easily in the presence of radiation or ions, suggesting association with dust grains or icy mantles.

Conclusions:

• PH3's stability and formation pathways are clarified.
• Radiation and ion-induced decomposition limit gas-phase PH3 abundance.
• Observation of PH3 is favored on interstellar dust grains and icy mantles, impacting phosphorus astrochemistry.