Negative Atmospheric Pressure Chemical Ionization of Chlorinated Hydrocarbons Studied by Ion Mobility Spectrometry...

Negative polarity atmospheric pressure chemical ionization of selected chlorinated hydrocarbons (tetrachloromethane CCl₄ and hexachloroethane C₂Cl₆, dichloromethane CH₂Cl₂, trichloromethane CHCl₃, 1,1,1,2-tetrachloroethane 1,1,1,2-C₂H₂Cl₄, 1,1,2,2-tetrachloroethane 1,1,2,2,-C₂H₂Cl₄ 1,1,2-trichloroethane 1,1,2-C₂H₃Cl₃, and 1,1,2-trichloroethane 1,1,2-C₂HCl₃) was studied using ion mobility spectrometry (IMS) and IMS combined with time-of-flight mass spectrometer (IMS-TOF MS) techniques, in the dry air and at two different drift gas temperatures (323 and 373 K). The ionization was performed using the O₂^-CO₂(H₂O)_0,1 reactant ions (RIs), and the dominant ionization reaction was the dissociative electron transfer. The ionization resulted in the appearance of Cl^- ions for all substances and [O₂H..Cl]^- ions, which were absent in the case of perchlorinated substances. The quantum-chemical calculations at the density functional theory level of theory using the ωB97X-D/aug-cc-pVTZ method were performed to calculate the thermochemical data (heats of formations, electron affinities, reaction enthalpies) for RIs, neutral substances, neutral fragments, and the anionic fragments. The calculations supported the experimental observations regarding the endothermicity of the Cl^- channel for all substances and the exothermicity of the [O₂H..Cl]^- channel for the tetrachloro- and trichloroethanes.