Cross-section energy dependence of the [C6H6–M]+ adduct formation between benzene molecules and alkali ions (M = Li, Na, K)

Abstract

The association reactions of benzene molecules with alkali ions M(+) (Li(+), Na(+) and K(+)) under single collision conditions have been studied using a radiofrequency-guided-ion-beam apparatus and mass spectrometry characterization of the different adducts. Cross-section energy dependences for [M-C(6)H(6)](+) adduct formation have been measured at collision energies up to 1.20 eV in the center of mass frame. All excitation functions decrease when collision energy increases, showing the expected behaviour for barrierless reactions. From ab initio chemical structure calculations at the MP2(full) level, the formation of the adducts makes evident the alkali ion-benzene non-covalent chemical bond. The cross-section energy dependence and the role of radiative cooling rates and unimolecular decomposition on the stabilization of the energized collision complex are also discussed.

Experimental and ab initio studies of the reactive processes in gas phase i-C3H7Br and i-C3H7OH collisions with potassium ions

“…where n is the target gas density in the collision cell and l the effective path length. Both n and l values had been obtained in a previous calibration experiment 23 by comparing our results with those described by Koizumi and Armentrout. 24 Using this procedure cross sections can be measured in absolute units, but with an uncertainty of around 30% or even larger.…”

Do Cation⋅⋅⋅π Interactions Always Need to be 1:1?

“…The calculated binding energies are in good agreement with the experimentally determined values obtained by collision induced dissociation (CID). [25] For example, the experimental binding energies for the mono-ion adducts of lithium, sodium and potassium ion with benzene are À38.5, À21.9 and À17.5 kcal mol À1 , respectively, while the calculated BSSE-cor- ], respectively. From Table 1 it is evident that the contribution of dispersion forces to the stabilization of cation···p complexes is significant (~2-3 kcal mol À1 to the binding energies).…”

The role of Li+ ions in the gas phase dehydrohalogenation and dehydration reactions of i-C3H7Br and i-C3H7OH molecules studied by radiofrequency-guided ion beam techniques and ab initio methods

“…III B and IV B, the formation of adducts with the M1 structure can be interpreted as mainly due to long range ion-molecule interactions. This follows from the analysis of the quantum chemistry valence molecular orbitals in which the contribution of the lithium atomic orbitals can be completely neglected, pointing to an essentially non-covalent interaction between both adduct partners (similar results were also found for other alkali ion-molecule systems [10][11][12] ). Taking into account that both i-C 3 H 7 Br and i-C 3 H 7 OH are both polar and polarizable, the former containing a highly polarizable, big-sized bromine atom and the latter the polar OH group, an important electrostatic ion-molecule interaction can be expected in both cases.…”

“…This has been used to research adducts' formation of alkali ions with polar 11 and nonpolar molecules 12 and more recently, some reactions involving halogenated organic compounds and alcohols as commented below. a) Author to whom correspondence should be addressed.…”