Equilibrium geometries, relative energies and thermodynamic properties of Si2H4 isomers have been obtained with the coupled cluster method (CCSD(T)) and aug-cc-pVXZ (X = 2-5) basis sets with next complete-basis-set extrapolations. Transition states between low-energy isomers were also computed. The global minimum structure corresponds to the trans-bent C-2h isomer and the monobridged C-1 isomer has been found to be almost isoenergetic to the silylsilylene C-s one. After including all necessary corrections, standard heats of formation of Si2H4 isomers are found to be equal to 66.0, 72.4, 73.0, 86.1 and 88.6 kcal/mol for the trans-bent C-2h disilene, monobridged C-1, silylsilylene C-s, dibridged trans C-2h and dibridged cis C-2v isomers, respectively. (C) 2008 Elsevier B. V. All rights reserved.