The negative ion at m/z 20 observed at atmospheric pressure corona discharge ionization mass spectra has been identified by supplying the vapors of deuterium oxide (D 2 O) and H 2 18 O. From the mass shifts of the ion at m/z 20 observed with D 2 O and H 2 18 O, it was suggested that the chemical composition of the ion at m/z 20 is to be H 4 O. Further mass shift from m/z 20 to 22 was observed by supplying the vapor of perfluorokerocene, suggesting the chemical composition of H 3 F. The chemical compositions of the negative ions H 4 O - and H 3 F - were consistence with the dipole-bound complex states between hydrogen H 2 and polar molecules such as H 2 O and hydrogen fluoride (HF) having dipole moments beyond a critical dipole moment of 1.625 D, theoretically proposed by Skurski and Simons. The ionic chemical compositions and structures of H 4 O - and H 3 F - obtained with density functional theory calculations implied that both dipole-bound complex H 2 O - …H 2 and HF - …H 2 can be formed by exothermic reactions by which H 2 molecule is complexing with negative ions H 2 O - and HF - , respectively.