The local mode model in silanes and germanes

We have gathered the known experimental data concerning the stretching vibrational energy levels of SiH4 and GeH4 and their deuterated derivative including the recent overtone data in 4 4 the visible range. Using the local mode model developed by Halonen and Child, the two Morse function parameters a, D e and the interbond potential coupling parameters frr' were fitted to reproduce the XH4(X = Si or Ge) energy levels. A root mean square deviation of 0·6 cm-1 was 4 achieved for both species. The same parameters were used to predict the energy levels of XD4, XHD3 and XH3D. The differences between the observed and predicted energy levels show 3 3 slight but systematic deviations for the XD stretching levels which are discussed in relation with possible anharmonic interactions between the stretching and the bending modes and with the mass dependence of the indirect kinetic and potential couplings of the XH or XD bond oscillators through the bend.