THE STRUCTURE OF THE METHANOL RADICAL-CATION - AN ARTIFICIALLY SHORT C-O BOND WITH MP2 THEORY

A detailed reinvestigation of the structure of the methanol radical ca tion has been undertaken using a variety of correlated theoretical pro cedures. These include the B3-LYP density functional method, second-or der Moller-Plesset theory (MP2), quadratic configuration interaction ( QCISD, QCISD(T)), Brueckner doubles (ED) and coupled-cluster theory (C CSD(T)), At the highest level of theory employed in this study (CCSD(T )/6-311G(df,p)), the preferred structure of the methanol radical catio n has an eclipsed conformation and a C-O bond length of 1.370 Angstrom . The structure is found to be strongly influenced by hyperconjugation . MP2, in combination with large basis sets, overestimates the effects of hyperconjugation, predicting CH3OH.+ to have a C-O bond length of less than 1.3 Angstrom. The use of a moderately large basis set that i ncludes f-functions on the heavy atoms, and a high-level electron corr elation procedure, are important in accurately determining the structu re of the methanol radical cation.