Photoionization studies of GeHn (n=2–4)

The adiabatic ionization potential of GeH+4 (GeH4) is measured by photoionization mass spectrometry to be ≤10.53 eV and perhaps as low as 10.44 eV. This is about 0.8 eV (∼9 vibrational quanta) lower than the value reported by photoelectron spectroscopy. This result, analogous to that found for SiH+4 (SiH4), implies a marked Jahn–Teller distortion of GeH+4. The appearance potentials of GeH+2 and GeH+3 from GeH4 are ≤10.772±0.009 eV and <11.657±0.01 eV, respectively. The reaction of F atoms with GeH4 generates GeH3, GeH2 (weakly), and some atomic germanium. The adiabatic ionization potential of GeH3 is ≤7.948±0.005 eV; that of GeH2 is ≤9.25 eV. Together with auxiliary information, limits (more probable values) of the incremental bond energies, in kcal/mol, are found to be D0 (H3Ge–H) <85.5 (82±2); D0 (H2Ge–H) >56.4 (59); D0 (HGe–H) <68.9 (66); and D0 (Ge–H) >53.7 (63). These specific bond energies, when appropriately normalized, display the same pattern as the SiHn (but not the CHn) bond energies and provide a basis for estimating the corresponding SnHn bond energies.