Electronic states and potential energy surfaces of PdH2: Comparison with PtH2

Abstract

Complete active space MCSCF (CASSCF) followed by multireference singles and doubles configuration interaction (MRSDCI) calculations are carried out on 13 electronic states of PdH2 and 9 electronic states of PdH+ . The bending potential energy surfaces of 1A1 and 3A1 electronic states were obtained. The 1A1 surface contains two bent minima (θe =30° and θe =62°) and a higher linear minimum separated by a saddle point. The 3A1 surface is relatively flat in the region of the saddle point. The Pd(1S0 ) atom forms a weak complex with H2 but inserts spontaneously into H2 while the Pd(3D3 ) atom has to surmount a large barrier for insertion into H2. The spin–orbit effects for the electronic states of PdH2 are estimated through relativistic configuration interaction calculations of PdH+ whose d Mulliken population is close to that of the d population of PdH2. The ground state of PdH2 is found to be a weakly bound bent 1A1 state with θe =30° and re (Pd–H)=1.67 Å. The electronic state and potential energy surfaces of PdH2 are compared with PtH2. The Pt–H bond is found to be stronger than the Pd–H bond mainly due to relativistic effects. The Pd–H bonds are more ionic than the Pt–H bonds.