Abstract: By means of ab initio calculations of MP₂/6-311+G(2d, 2p) method, the optimized geometryof the CH₂F₂…H₂O complex is obtained.The structure of a subunit in the complex is similar to that of itsmolecule(CH₂F₂, H₂O).It was found that the geometry structure of the complex CH₂F₂...H₂O is close toits experimental structure.∠F…H-O= 116.5°is a large deviation from a strictly linear H-bond.It is aresult that a strong π-type secondary hydrogen bond formed.Using a probing point charge to detect theorientations of the lone pairs at atom Oof the CH₂F₂…H₂O, we establish here a π-type secondary H-bondinteraction model.Because long pair ni and CH_i(i=1, 2) is almost parallel and in a plane, the additionalsecondary H-bond between n_i and CH_i(i=1,2) formed.The double π-type H-bond is very strong.Fur-thermore, the stabilized energy of bending H-bond comes from π-type H-bond (△E_sb= -0.0658eV) isalso calculated.The stabilized energy of bending H-bond is very large, 46.6% of the interactrion energy of CH₂F₂…H₂O complex.It is shown that the double π-type secondary hydrogen bond is very strong.

Key words: CH₂F₂…H₂O, Ab initio, π-type secondary hydrogen bond