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.

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.