The photoelectron spectra of methane, silane, germane and stannane

The photoelectron spectra of the group iv hydrides, CH4, SiH4, GeH4 and SnH4 are shown to be due to ionization from valence ax and t2 orbitals analogous to the s and p orbitals of the corresponding inert gases. The associated vibrational pattern of the ax bands is a simple progression of the breathing vibration. That of the t2 systems shows the effect of Jahn-Teller splitting part of which converts to spin-orbit splitting for the heavier hydrides. The bond lengths and angles of the ionized states are evaluated approximately from the structures and. intensities of the band patterns. The experimental results give some support for theoretical calculations by Dixon which indicate that the triple degeneracy of the (t2)-1 state is removed by distortion to a D2d conformation, its low energy 2B2 component involving a fairly long progression in the v2 vibration and, in the case of methane, progressions in v1 containing several members. This agrees with our observations but our analysis of the spectra indicates that this state of CH4+ takes up a conformation that is almost square coplanar with an extremely low inversion barrier. The 2B2 ionized states of SiH4, GeH4 and SnH4 though considerably distorted do not become coplanar.