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Gas phase reactive collisions between lithium ions and i-C3H7X (X = Br, OH) molecules have been studied under single collision conditions in the center of mass (CM) 0.01-10.00 eV energy range using a radiofrequency-guided ion beam apparatus. Mass spectrometry analysis of the products did show the presence of [C3H6-Li]+, [HX-Li]+, C3H7 +, and C2H3 + as well as of the [Li-i-C3H7Br]+ adduct while [Li-i-C3H7OH]+ was hardly detected. For all these reactive processes, the corresponding cross sections have been measured in absolute units as a function of the CM collision energy. Quantum chemistry ab initio calculations done at the second order Möller Plesset level have provided relevant information on the topology of the potential energy surfaces (PESs) where a reaction takes place allowing the characterization of the stationary points on the respective PESs along their reaction pathways. The connectivity of the different stationary points localized on the PESs was ensured by using the intrinsic reaction coordinate (IRC) method, confirming the adiabatic character of the reactions. The main topology features of the reactive PESs, in the absence of dynamical calculations, were used to interpret at the qualitative level the behavior of the experimental excitations functions, evidencing the role played by the potential energy barriers on the experimental dynamics of the reactions. Reaction rate constants at 303.2 K for different reactions have been calculated from measured excitation functions. [ABSTRACT FROM AUTHOR]

Collisions between potassium ions and neutral i-C3H7Br and i-C3H7OH, all in their electronic ground state, have been studied in the 0.10-10.00 eV center of mass (CM) collision energy range, using the radiofrequency-guided ion beam technique. In K+ + i-C3H7Br collisions KHBr+ formation was observed and quantified, while the analogous KH2O+ formation in K+ + i-C3H7OH was hardly detected. Moreover, formation of the ion-molecule adducts and their decomposition leading to C3H7 + and either KBr or KOH, respectively, have been observed. For all these processes, absolute cross-sections were measured as a function of the CM collision energy. Ab initio structure calculations at the MP2 level have given information about the potential energy surfaces (PESs) involved. In these, different stationary points have been characterized using the reaction coordinate method, their connectivity being ensured by using the intrinsic-reaction-coordinate method. From the measured excitation function for KHBr+ formation the corresponding thermal rate constant at 303 K has been calculated. The topology of the calculated PESs allows an interpretation of the main features of the reaction dynamics of both systems, and in particular evidence the important role played by the potential energy wells in controlling the reactivity for the different reaction channels. [ABSTRACT FROM AUTHOR]

Inelastic electronically non-adiabatic reactions between Na+ ions and neutral ZnBr2 molecules, both in their electronic ground state, have been studied using crossed beams techniques and measuring the decaying emission radiation of the excited species produced. The fluorescent emission corresponding to Na(3 2P) produced by a charge transfer reaction was observed, as well as that corresponding to the decay of Zn(4s 5s 3S), generated by dissociation of the neutral target molecule, to Zn(4s 4p 3P). The phosphorescent decaying emission of Zn*(4s 4p 3P) to the zinc ground state was also observed. For each emission process, the cross section energy dependences have been measured in the 0.10-3.50 keV energy range in the laboratory system. The ground electronic state of the (NaZnBr2)+ collision system has been characterized by ab initio chemical structure calculations at the second order Möller-Plesset perturbation level of theory using pseudo-potentials. By performing restricted open shell Hartree-Fock calculations for C2v geometries, four singlet and four triplet potential energy surfaces of the system have been calculated and used to interpret qualitatively the observed reactions. A simple two-state dynamical model is presented that allows an estimation of the maximum values for measured cross sections at high collision energies to be made. [ABSTRACT FROM AUTHOR]

Reactive collisions between Li+ ions and i-C3H7Cl molecules have been studied in the 0.20–12.00 eV center-of-mass energy range using an octopole radio frequency guided-ion beam apparatus recently developed in our laboratory. At low collision energies, dehydrohalogenation reactions giving rise to Li(C3H6)+ and Li(HCl)+ are the main reaction channels, while at higher ones C3H7+ and C2H3+ become dominant, all their reactive cross sections having been measured as a function of the collision energy. To obtain information about the potential energy surfaces (PESs) on which the reactive processes take place, ab initio calculations at the MP2 level have been performed. For dehydrohalogenations, the reactive ground singlet PES shows ion-molecule adduct formation in both the reactant and product sides of the surface. Following the minimum energy path connecting both minima, an unstable intermediate and the corresponding barriers, both lying below the reactant’s energy, have been characterized. The entrance channel ion-molecule adduct is also involved in the formation of C3H7+, which then generates C2H3+ via an CH4 unimolecular elimination. A qualitative interpretation of the experimental results based on ab initio calculations is also included. [ABSTRACT FROM AUTHOR]

Inelastic and charge-transfer excitation processes in collisions between ground-state neutral Mg atoms and K+ ions have been studied by means of a crossed molecular-beam technique. Decay fluorescent emissions from Mg(3 1P1),Mg(4 3S1), and Mg(3s13d1,3 3D3,2,1) as well as the phosphorescent emission due to Mg(3 3P1) have been observed from excited Mg atoms and the charge-transfer emission decays from K(4 2P3/2,1/2),K(5 2P3/2,1/2),K(6 2S1/2), and K(4 2D5/2,3/2) for excited K atoms. The corresponding absolute cross-sections values versus collision energy functions were determined in the 0.10–3.80 keV laboratory energy range. In order to interpret the experimental results, accurate ab initio full configuration-interaction calculations using pseudopotentials have been performed for the (Mg–K)+ system, giving a manifold of adiabatic singlet and triplet potential-energy curves correlating with the different collision channels, which allow a qualitative interpretation of the emission excitation functions measured for the different processes studied. A comparative study with other Mg-alkali ion systems previously studied is also included. [ABSTRACT FROM AUTHOR]

Inelastic collision processes between neutral Mg atoms and Rb+ ions, both in their ground states, have been studied by means of a crossed molecular beam technique measuring the decay fluorescence of the excited species formed. Emissions corresponding to Mg(3 1P1), Mg(3 3D3,2,1), and Mg(4 3S1), formed by direct target excitation, Rb(5 2P3/2,1/2), Rb(6 2P3/2,1/2) produced by electron capture and also the phosphorescent emission due to decay of Mg(3 3P1), have been detected and the corresponding absolute cross-section values measured both as total values and resolved into their J states. No polarization measurements could be made. Ab initio calculations using pseudopotentials have been performed and from these a manifold of adiabatic energy curves correlating with the different entry and exit channels have been obtained, allowing to propose a qualitative interpretation of the results, such as the shape of the cross section vs energy for different transitions and the oscillating nature of the branching ratios due to interference effects. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]