The HXeCCH center dot center dot center dot H2C2 complex has been characterized by IR spectroscopy in a xenon matrix and ab initio calculations. This species exhibits a blue shift of the H-Xe stretching mode (19-28 cm(-1)) in comparison with the HXeCCH monomer, which indicates stabilization of the H-Xe bond upon complexation. The complex results from annealing-induced diffusion of acetylene molecules above 50 K to isolated HXeCCH formed at lower temperature. In addition, a weak absorption with a blue shift of +51 cm(-1) was tentatively assigned to the HXeCCH complex with two acetylene molecules. These experimental observations are supported by ab initio calculations. (C) 2009 Elsevier B.V. All rights reserved.