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, O_(2)), where larger clusters with n ≥4 were not detected. The mechanisms for the formation of the HF, F~(?)(HF)_(n) , and O_(2)~(?)(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 (E _(CM)). These E _(CM) values were consistent with the values of 0.995, 1.308, and 2.048?eV, respectively, obtained by ab initio calculations. The stability of [O_(2)(HF)_(n) ]~(?) (n =1–4) was discussed on the basis of the bond lengths of O_(2)H–F~(?)(HF)_(n) and O_(2)~(?)H–F(HF)_(n) obtained by ab initio calculations. The calculations indicated that [O_(2)(HF)_(4)]~(?) separated into O_(2)H and F~(?)(HF)_(3).