Accurate structural parameters and torsional barrier heights of hydrogen peroxide were determined using the CCSD(T) method with the correlation consistent basis set. The basis set incompleteness error was circumvented using the appropriate extrapolation schemes suitable for correlation consistent calculations and core-correlation correction was also considered. The estimated CCSD(T) basis set limit torsional barrier heights are 357 cm(-1) for trans- and 2496 cm(-1) for cis-configuration, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.