Study on the Gas-phase Structure of Water Dimer Radical Cation Using Mass Spectrometry

Water is one of the most important compounds and plays an important role in biological process, chemical synthesis and material science. Thus, studies about water and related particles water radical cations are always the top research fields. In this work, water dimer radical cation (H2O)2+• was prepared using home made low energy corona discharge device at ambient condition, and its structure was further studied using collision induced dissociation (CID) experiment and isotope labelling method. The dissociation results showed that (H2O)2+• (m/z 36) will lose OH• and H2O to give ions of m/z 19 (H2OH+) and m/z 18 (H2O+•), competitively, revealing that (H2O)2+•can exist in two different structures, including ［H2OH+—•OH］ (hydrogen atom bound structure (A)) and ［H2O∴OH2］+ (oxygen oxygen atom bound structure (B)). Structure A is asymmetry and structure B is symmetry. Furthermore, isotopic labeled experiments were conducted using deuterated water (D2O) and 18O-enriched water (H218O). The dissociation of (D2O)2+•(m/z 40) gave the corresponding protonated water D2OD+ (m/z 22) and water radical cation (D2O)+• (m/z 20). Dissociation of (H2O•D2O)+•(m/z 38) produced the protonated water H2OD+ (m/z 20)/D2OH+ (m/z 21), and water radical cation H2O+• (m/z 18), HOD+• (m/z 19), D2O (m/z 20)+•. In 18O-enriched water (H218O) labelled isotopic experiments, (H2O•H218O)+•(m/z 38) also was dissociated into its corresponding protonated water H2OH+(m/z 19)/H218OH+(m/z 21) and water radical cation H2O+• (m/z 18) and H218O+•(m/z18). The CID and the isotope labelling results indicated that water dimer radical cation (D2O)2+•, (H2O•D2O)+• and (H2O•H218O)+•also exist A and B two structured forms. In conclusion, two structures of water dimer radical cation (H2O)2+•will further reveal that mass spectrometry may help to elucidate chemical mechanism related with (H2O)2+•in the biological processes and chemical reactions.