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 (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.