Density - functional theory (DFT) B3lLYP/6 - 31G^* approach has been employed to calculate the possible configurations ammonium - bibenzene (C~6H~6…NH~4^+…C~6H~6) complex. The calculation results indicate that the most stable structure of the complex is the configuration where the ammonium cation located between two benzenes with two hydrogen atoms pointing to each benzene ring.The calculated IR spectrum shows that the geometry is reasonable.The bond length, total atomic charges,the coefficiet of the molecularorbital, frontier orbital energys, and Mullicken bonding population of the complex indicate that the binding between the ammonium and two benzenes involved the s-π interaction between hydrogens of ammonium and the carbon atoms of benzenes near to the hydrogens of ammonium, with electron transfer occured from the two benzne rings to ammonium,forminmg a charge transfer complex.The calculated results also imply that,similar to that of the ammonium caton-benzene transfer complex, the interaction characteristic of the ammonium cation-bibenzene complex is a typical hydrogen bond.The calculated thermodynamic parameters demonstrate this feature.The nomal mode analysis of the predicted vibrational frequency shows that the characteristic vibration mode of the complex is located at about 230cm^-^1, correspondeding to the back and forth vibration of the ammonium cation paralleled to the bezene rings.

Key words: HYDROGEN BONDS, CONFIGURATION, AMMONIUM, PHENYL KETONE