Electron Spin Resonance Study of PH4 Trapped in Solid Krypton

Abstract

The ESR spectrum of the PH4 radical, produced by the vacuum uv photolysis of phosphine in solid krypton, is reported for the first time. The spectrum centered at g=2.002 is consistent with four equivalent hydrogens, and shows only isotropic hyperfine splittings (ap = 973.8 ± 2.0 G and aH = 21.0 ± 2.0 G). The observed equivalence of the hydrogens contrasts with the spectra reported previously for PF4. A treatment of the energies of configurations for PH4 with the CNDO molecular orbital method indicates the optimum geometry to be C2v with HPH angles equal to 162° and 97°; additionally, the energy barrier to pseudorotation through a C3v intermediate is estimated to be relatively low (approximately 6 kcal mole−1), and this leads to the possibility that the equivalence of the hydrogens is due to internal tunneling motions.