We report an empirically adjusted potential energy surface for C2H2 that describes acetylene/vinylidene isomerization. This new surface is based on a very recent fit to extensive ab initio electronic calculations obtained at the CCSD(T) level of theory, with an aug-cc-pVTZ basis [Chem. Phys. Lett. 368 (2003) 421]. The adjustments are made by a coordinate-scaling procedure that has been used previously to empirically adjust potentials. The adjustments are made based on full-dimensional converged quantum mechanical calculations of acetylene vibrational levels that have been accurately determined experimentally. (C) 2003 Elsevier B.V. All rights reserved.