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

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 (D₂O) and H₂¹⁸O. From the mass shifts of the ion at m/z 20 observed with D₂O and H₂¹⁸O, it was suggested that the chemical composition of the ion at m/z 20 is to be H₄O. Further mass shift from m/z 20 to 22 was observed by supplying the vapor of perfluorokerocene, suggesting the chemical composition of H₃F. The chemical compositions of the negative ions H₄O^- and H₃F^- were consistence with the dipole-bound complex states between hydrogen H₂ and polar molecules such as H₂O 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 H₄O^- and H₃F^- obtained with density functional theory calculations implied that both dipole-bound complex H₂O^-…H₂ and HF^-…H₂ can be formed by exothermic reactions by which H₂ molecule is complexing with negative ions H₂O^- and HF^-, respectively.