The geometries for the benchmark H 2 O+HNCO reaction are obtained using the CCSD(T) method via the CFOUR 2.0 75 software package. The Dunning cc-pVQZ basis set is utilized for all stationary points except for the van der Waals complexes which are optimized with the aug-cc-pVTZ basis set to properly describe long range interactions. Harmonic vibrational frequencies are obtained for each stationary point using the same level of theory as the geometry optimization and verify each geometry as a minimum or first-order saddle point (transition state). The connectivity of each stationary point is verified by performing qualitative intrinsic reaction coordinate (IRC) scans. Relative energies of each stationary point are further refined utilizing the focal point method of Allen and coworkers. The SCF/cc-pVXZ (X=Q,5,6) energy is extrapolated using the three point extrapolation formula of Feller 82 (E HF (X) = E ∞ HF + ae -bX ) and the correlation energy up to CCSD(T)/cc-pVXZ (X=4,5) is extrapolated using the two point formula of Helgaker 83 (E corr (X) = E ∞ corr +aX -3 ) towards the complete basis set (CBS) limit .