HCuCO is studied using a large Gaussian basis set at the coupled clust
er singles and doubles level of theory, including a perturbational est
imate of the connected triples (CCSD(T)). In contrast with CuCO, HCuCO
is linear. The Cu-CO bond in HCuCO is significantly stronger than in
CuCO. These differences between HCuCO and CuCO are discussed in terms
of the Cu-H bond polarizing the Cu 4s electron away from the CO.