Direct density functional theory B3LYP was employed to obtain the optimized geometries of the ground state for 1,2,4-triazine-(H₂O)_n (n＝1, 2, 3) complexes. All calculations indicate that the 1,2,4- triazine-water complexes on the ground state have strong hydrogen bonding interaction, and the structure having an N…H—O hydrogen bond and a chain of water molecules, which is terminated by an O…H—C hydrogen bond, is most stable. The first singlet (n, π^*) vertical excitation energy of the monomer 1,2,4-triazine and the hydrogen bonding complexes between 1,2,4-triazine and water has been investigated by time-dependent density functional theory.

Key words: 1,2,4-triazine, hydrogen bond, density functional theory