Theoretical comparison of the linear and bent structures for the weakly bound CO2---HF complex

摘要

Density-functional theory method (DFT) B3LYP/6-311++G(3df,2pd) and Moller-Plesset perturbation method (MP2) MP2/6-311++G(3df,2pd) of Gaussian 03 were selected for the theoretical study of weakly bound CO2---HF complex. In addition to the well-known linear structure, the various bent structure complexes were also found in this work. The self-consistent energy differences were only around 0.02 kJ/mol between the bent structure and linear structure by comparison. From the results of H-bonding distance, d(HF) elongation and red shift of v(HF) vibration frequency, all the evidence shows that the H-bonding effect in the bent structure is stronger than the linear structure. However, if one compares the Gibbs energy of the complex formation by temperature variation, it is very easily found that the linear form is favored under the thermal conditions of most temperatures whenever T >= 40 K. Such a fact is consistent with the former spectroscopic observed result of Klemperer et al.