Identification of Negative Ion at m/z 20 Produced by Atmospheric Pressure Corona Discharge Ionization under Ambient Air.

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 (D2 O) and H2 18 O. From the mass shifts of the ion at m/z 20 observed with D2 O and H2 18 O, it was suggested that the chemical composition of the ion at m/z 20 is to be H4 O. Further mass shift from m/z 20 to 22 was observed by supplying the vapor of perfluorokerocene, suggesting the chemical composition of H3 F. The chemical compositions of the negative ions H4 O- and H3 F- were consistence with the dipole-bound complex states between hydrogen H2 and polar molecules such as H2 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 H4 O- and H3 F- obtained with density functional theory calculations implied that both dipole-bound complex H2 O- …H2 and HF- …H2 can be formed by exothermic reactions by which H2 molecule is complexing with negative ions H2 O- and HF- , respectively.