Solvation of Li+ by Acetone, THF, and Diethyl Ether in the Gas Phase and the Ion−Molecule Association Mechanism

Abstract

Fourier transform ion cyclotron resonance spectrometry has been employed to study the solvation of the Li+ ion with acetone, tetrahydrofuran (THF), and diethyl ether (DEE) in the gas phase. LiILi+ triple ions are produced in the ICR cell by the laser desorption ionization of a lithium iodide/dibenzo-18-crown-6-ether matrix pasted on a Teflon substrate. All O donors abstract Li+ from the triple ion and form solvated complexes with a maximum solvation number of three at room temperature, around 10-6 Torr. All third solvent binding energies are determined from van't Hoff plots. Structures and energetics of the Li+·(S)n complexes, where n = 1−4 for acetone and THF and n = 1−3 for DEE, have been calculated at the Hartree−Fock level with a 6-311+G(d,p) basis set. Solvation enthalpies and free energies are calculated, and solvent binding enthalpies are compared with experiments. The kinetics of solvent exchange and the association reactions of Li+·(acetone-h6)(acetone-d6) with a 1:1 acetone-h6/acetone-d6 mixture have been measured as a function of pressure. The lifetime of the collision complexes are derived and compared with phase space theory calculations. The isotope effect on the radiative cooling rate is discussed.