ESR of Free Radicals Trapped in Inert Matrices at Low Temperature: P, PH2, and As

Free radicals produced by γ irradiation of PH3 and of AsH3 in dilute solution in a krypton matrix at 4.2°K have been studied with electron spin resonance. For the PH3 solution, PH2 radicals as well as H and P atoms were observed. For the AsH3solutions, only H and As atoms were observed. For the PH2 radicals, the observed ESR constants are: Af(31P) = 80 G, Af(H) = 18 G, and g = 2.0087. For the P atoms, Af(31P) = 30.5 G and g = 2.0027. For the As atoms, Af(75As) = 11.2 G and g= 1.9975. From the P and H couplings it is concluded that the P bonding orbitals of PH2 are sp2 hybrids with 27% scharacter. From the line shapes it is concluded that the PH2 radical rotates in the krypton matrix.