MOLECULAR-COMPLEX BETWEEN LITHIUM AND FORMALDEHYDE - AN AB-INITIO MOLECULAR-ORBITAL STUDY

The molecular complex formed between the formaldehyde molecule and the lithium atom was studied bp ab initio molecular orbital calculations. Electron correlation energies were calculated by both the Moller-Ples set perturbation and multireference configurational interaction (MRCI) methods. Three local minima were located in the electronic ground sta te of the complex at both the MP2/6-31+g(2d,p) and MRCI(4s3p2d/3s2p)le vels. Two of the local minima are ion pair in nature (Li+CH2O-), and t he third one has the character of the alkali metal atom-Lewis base bon ding (Li...CH2O). The latter is designated as a complexation pair stat e. The bond dissociation energies are 20.70 and 19.14 kcal/mol for the two ion pair states and 7.73 kcal/mol for the complexation pair state , respectively, at the MP4/6-311+g(2d,p) level. Consistent results wer e obtained with the MRCI approach. The energy barriers between the ion pair states and the complexation pair; state were searched at MRCI le vel, and the transition states were determined. The general features o f the adiabatic potential surface of the electronic ground state of th e complex were described. The effects of complexation on the geometry, vibrational frequencies, and the electronic structure of formaldehyde were also discussed. For completeness, the positively charged ion of the complex was also studied, and the corresponding ionization potenti al of the neutral states were calculated.