Abstract: MP2 and density-functional theory B3LYP methods with 6-31+G** basis sets have been used to optimize the possible geometries of the o-xylene…ammonia complexe.The calculation results show that the most stable geometries of the o-xylene…ammonia complexe are the ammonia located above the benzene ring.The calculated IR spectrum show that these structures are reasonable.The bond length,total atomic charge,the theoretical thermodynamic parameters,frontier orbital energies of the complexes indicate that the o-xylen...