CORRELATED CALCULATIONS OF INDIRECT NUCLEAR-SPIN SPIN COUPLING-CONSTANTS FOR XH4 (X=SI, GE, AND SN)

We report multiconfigurational linear response calculations of the one -bond and geminal indirect nuclear spin-spin couplings constants in Si H4, GeH4, and SnH4. Results of a basis set study on SnH4 using 13 diff erent basis sets on Sn are given, showing the effects on the individua l contributions to the coupling constant. In addition to the more conv entional choice of active orbital space (one correlating orbital for e ach strongly occupied valence orbital), calculations employing extende d active spaces were carried out. The results are compared with availa ble experimental data showing that correlation effects are very import ant. For the one-bond couplings good agreement with experiment, within 1-5%, is obtained, whereas the geminal proton-proton couplings show l arger deviations. The calculations reported here are, to our knowledge , the first that take into consideration correlation effects in all fo ur contributions to the coupling constants for molecules as large as G eH4 and SnH4. All X-H couplings are dominated by the Fermi contact ter m while the picture is more diverse for the geminal couplings.