Table 1. Representative Incremental Focal Point Table for the Products of the C₂H + HNCO → C₂H₂ + NCO Reaction Relative to the Reactants (kcal mol^–1)^a.

basis set	HF	+δMP2	+δCCSD	+δ(T)	+δT	+δ(Q)	net
aug-cc-pVDZ	–23.32	+4.64	–4.01	+0.30	–0.10	–0.05	[−22.54]
aug-cc-pVTZ	–23.54	+4.52	–4.20	+0.27	[−0.10]	[−0.05]	[−23.09]
aug-cc-pVQZ	–23.34	+4.76	–4.11	+0.26	[−0.10]	[−0.05]	[−22.58]
aug-cc-pV5Z	–23.33	+4.80	–4.08	+0.25	[−0.10]	[−0.05]	[−22.51]
CBS limit	[−23.34]	[+4.83]	[−4.05]	[+0.25]	[−0.10]	[−0.05]	[−22.46]

^aAdditional focal point tables can be found in the Supporting Information. δ denotes the change in the relative energy with respect to the previous level of theory. The numbers in [ ] are obtained by the extrapolation schemes found in the Theoretical Methods section.