A selected ion flow tube investigation of the gas phase chemistry of Li+

Lithium ion attachment is assessed in this study as a possible means of chemical ionization in the selected ion flow tube-mass spectrometric (SIFT-MS) technique. Measurements using a selected ion flow tube (SIFT) operating at room temperature are reported for lithium ion association reactions with 21 neutral reagents. The reagents ranged from small molecules such as CH4 and CO, for which the association rate coefficients were very small, to larger organic molecules such as C6H6 and C5H5N, for which the association rates approached the collision rate coefficient. The bond dissociation energy (BDE) of the (Li-X)+ bond was an important factor in deciding whether or not lithium ion association might be used in SIFT-MS. The attached molecule, X, in the LiX+ molecular ion is switched out by H2O for those species having BDEs <137 kJ mol−1. For reactants having BDEs ≥137 kJ mol−1, some switching out by water occurred in Li(X)n+ resulting in Li+·(H2O)n terminal ions. For those reagents having BDEs ≫ 137 kJ mol−1, mixed LiXm+(H2O)n clusters were observed.