The absolute cross-section of the reactive collision of P⁺(³P) with D₂: a combined theoretical and experimental study

In this work, we combine theoretical and experimental methods to study the P⁺(³P) + D₂ → PD⁺ + D reaction. As a result, the absolute cross-section as a function of collision energy is obtained. Experimentally, the cross-section is measured using the guided ion beam technique (GIB), where P⁺ is produced by VUV photons at the SOLEIL synchrotron using PCl₃ as a precursor. Theoretically, the cross-section is calculated from first principles. The potential energy surfaces of the three electronic states correlating with the P⁺(³P) are constructed by fitting MRCI points, and reaction dynamics are performed on each of them independently, hence neglecting couplings. The total cross-section is then obtained from the weighted contribution of each considered electronic state. Our findings show good agreement between the measured and calculated cross-sections, with a small discrepancy indicating that spin-orbit and non-adiabatic coupling, not considered in this work, may play a role in this reaction. The results hereafter presented demonstrate that the chemistry of the third-row atomic cations with molecular hydrogen is generally unfavoured, unlike their second-row homologues, thus manifesting the existence of boundaries to the applicability of the so-called chemical analogy (i.e., assuming the same chemical behaviour for elements belonging to the same group).