Collision-Induced Dissociation Study of Strong Hydrogen-Bonded Cluster Ions Y−(HF)n (Y=F O2) Using Atmospheric Pressure Corona Discharge Ionization Mass Spectrometry Combined with a HF Generator

摘要

Hydrogen fluoride (HF) was produced by a homemade HF generator in order to investigate the properties of strong hydrogen-bonded clusters such as (HF)n. The HF molecules were ionized in the form of complex ions associated with the negative core ions Y⁻ produced by atmospheric pressure corona discharge ionization (APCDI). The use of APCDI in combination with the homemade HF generator led to the formation of negative-ion HF clusters Y⁻(HF)n (Y=F, O2), where larger clusters with n≥4 were not detected. The mechanisms for the formation of the HF, F⁻(HF)n, and O2⁻(HF)n species were discussed from the standpoints of the HF generator and APCDI MS. By performing energy-resolved collision-induced dissociation (CID) experiments on the cluster ions F⁻(HF)n (n=1–3), the energies for the loss of HF from F⁻(HF)3, F⁻(HF)2, and F⁻(HF) were evaluated to be 1 eV or lower, 1 eV or higher, and 2 eV, respectively, on the basis of their center-of-mass energy (ECM). These ECM values were consistent with the values of 0.995, 1.308, and 2.048 eV, respectively, obtained by ab initio calculations. The stability of [O2(HF)n]⁻ (n=1–4) was discussed on the basis of the bond lengths of O2H–F⁻(HF)n and O2⁻H–F(HF)_n obtained by ab initio calculations. The calculations indicated that [O₂(HF)₄]⁻ separated into O₂H and F⁻(HF)₃.