Ab initio calculations, using second-order Moller-Plesset perturbation theory with a 6-311++G(2d,2p) basis set, predict the stability of two novel compounds of monofluoroethene, CH2CHF, with the rare-gas atoms Ar and Kr. The dissociation energies to the lowest-energy fragmentation products, CH2CHF+Rg (Rg=Ar,Kr), were computed to be -528 and -449 kJ mol-1, respectively, at the coupled-cluster singles, doubles, and triples level of theory. Possible transition states (at second-order Moller-Plesset theory) via a C-Rg-F bending mode for these fragmentation reactions were also located with barrier heights of about 76 and 106 kJ mol(-1), for the Ar- and Kr-containing species, respectively. However, the Ar-containing species may not exist at all as it is less stable than the fragments CH2CH+F+Ar at the higher level of theory and may possibly dissociate via this route. (C) 2004 American Institute of Physics.