Accurate theoretical structures of radical cations containing unusually long bonds: the structures of CH3CH2OH.+, ĊH2CH2O+H2

A detailed investigation of the structures of CH3CH2OH.+ and its α- and β-distonic isomers, CH3ĊHO+H2 has been carried out using a variety of theoretical procedures. The methods employed include Hartree-Fock theory and a range of correlated procedures including second-order Møller-Plesset (MP2) theory, quadratic configuration interaction (QCISD, QCISD(T)), and coupled-cluster theory (CCSD, CCSD(T)), as well as the density functional theory procedures B3-LYP and B3-P86. It is found that the use of a reliable electron correlation procedure, as well as a reasonable sized basis set, are important in accurately determining the structure of such ions. At the highest level of theory employed in this study (CCSD(T)/6-311G(d,p)), CH3CH2OH.+ is predicted to poossess an unusually long CC bond (1.745 Å) while ĊH2CH2O+H2 is predicted to contain an unusually long CO (1.614 Å).