Potential energy surfaces of the (1)A(1) and B-3(1) states for XH(2) molecules (X=C, Si, Ge, Sn, Pb) are investigated with ab initio full valence multiconfigurational self-consistent field wave functions, using effective core potentials. Spin-orbit coupling is also calculated to construct relativistic potential energy surfaces. The relativistic potential energy surfaces an compared with the adiabatic nonrelativistic potentials. Simple one dimensional Landau-Zener transition probabilities are calculated at the minimum energy crossing points of XH(2) molecules to estimate the intersystem crossing probability.