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

Abstract

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 CH 4 and CO, for which the association rate coefficients were very small, to larger organic molecules such as C 6H 6 and C 5H 5N, 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 H 2O 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 +·(H 2O) n terminal ions. For those reagents having BDEs ≫ 137 kJ mol −1, mixed LiX m +(H 2O) n clusters were observed.