Supplementary Material

Detailed computational data (energies, optimized molecular geometries, harmonic vibrational frequencies, and infrared intensities) for the cationic species resulting from PH3, PD3, their homodimers, and heterodimers; additional EPR and FTIR spectra illustrating the formation of phosphine monomeric and dimeric radical cations from PH3 and PD3, simulated EPR spectra of different kinds of P2H3D3+• radical cations; accumulation profiles of cationic species upon X-irradiaion