Pt-Re small cluster interaction with H-2

The interaction of small Pt-Re clusters with H-2 is reported here through a b initio multiconfiguration self-consistent field (MC-SCF) calculations, pl us extensive multireference configuration interaction (MR-CI), variational and perturbative calculations. These calculations provide a cluster model f or the activation of hydrogen by Pt-Re bimetallic catalysts. It was found t hat the S-6(5d(5)6s(2)) Re atom ground state needs an important activation to induce very weak capture of separated hydrogen atoms, whereas in the low est excited states the activation energies are small or zero, with a very r easonable depth of well. The four lowest states of Pt-Re were found to be ( 4)Sigma(+), (6)Pi(yz), (6)Sigma(+) and (6)Pi(xz). Pt-Re interaction with H- 2 has been studied from both metal 'sides'. It was established that Pt-Re w ith the platinum side in the ground electronic (4)Sigma(+) state and in the lowest (6)Sigma(+) excited states is able to capture H-2 molecules without activation, whereas in the (6)Pi(yz) and (6)Pi(xz) excited states there is no capture. The rhenium side of Pt-Re in its four lowest states considered cannot capture the H-2 molecule. The interaction of Pt-2-Re with H-2, was studied also. For the ground B-2(2) electronic state and the low lying (2)A (1) electronic state the platinum moiety can spontaneously capture and brea k H-2. The rhenium side of Pt-2-Re(B-2(2)), however, can capture H-2 only a fter surmounting a small barrier, and the excited Pt-2-Re((2)A(1)) can spon taneously capture H-2 For Pt-2-Re in its low lying (4)A(1) electronic slate both metal sides capture and break H-2 after surmounting a small barrier.