Guided-Ion-Beam and ab Initio Study of the Li⁺, K⁺, and Rb⁺ Association Reactions with Gas-Phase Butanone and Cyclohexanone in Their Ground Electronic States

Abstract

The association reactions between Li(+), K(+), and Rb(+) (M) and butanone and cyclohexanone molecules under single collision conditions have been studied using a radiofrequency-guided ion-beam apparatus, characterizing the adducts by mass spectrometry. The excitation function for the [M-(molecule)](+) adducts (in arbitrary units) has been obtained at low collision energies in the 0.10 eV up to a few eV range in the center of mass frame. The measured relative cross sections decrease when collision energy increases, showing the expected energy dependence for adduct formation. The energetics and structure of the different adducts have been calculated ab initio at the MP2(full) level, showing that the M(+)-molecule interaction takes place through the carbonyl oxygen atom, as an example of a nontypical covalent chemical bond. The cross-section energy dependence and the role of radiative cooling rates allowing the stabilization of the collision complexes are also discussed.

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

“…Moreover, calculated molecular orbitals show a very small overlap of the potassium-centered atomic orbitals and the molecule-centered ones, in agreement with an essentially non-covalent ion-molecule interaction found in other alkali ion-molecule adducts. 32,33 Similar results are found for the [K-i-C 3 H 7 OH] + adduct (see Figs. 6(a) and 6(b)) with very small geometrical changes compared to the neutral i-C 3 H 7 OH molecule: the middle C-OH distance changes from 1.431 Å to 1.458 Å while the O-H one remains essentially the same (from 0.965 Å to 0.967 Å).…”

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.…”

“…The detailed analysis of the valence molecular orbitals of the [Li− −i-C 3 H 7 Br] + structure shows a negligible participation of the lithium's atomic orbital, clearly showing that the ion-molecule interaction is essentially non-covalent in nature, as was also observed in previous studies on similar systems. 11,19 The study of the reaction pathway leading from M1 to (1) and (2) products requires an exhaustive and wide characterization of the interaction energies which in the first step localizes a first order saddle point (0.457 eV below reactants' energy) associated with the transition state TS1. This has a single Hessian matrix negative eigenvalue with a 245.24 i cm 1 imaginary frequency.…”

“…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.…”

Mass spectrometric investigation of high-mass neutral species in the downstream region of Ar/CH4 plasmas

“…It has been found that the collisions between Li þ and neutral species exclusively lead to the production of Li þ adducts in the cases of hydrocarbons, 28 perfluorocarbons, 28,29 and ketones, 30,31 when the collision energy corresponds to room temperature. The exception is reported only in the case of C 3 H 7 Cl.…”