title: Collision-induced dissociation mechanisms of [Li(uracil)]+.
abstract: The collision-induced dissociation (CID) of the [Li(uracil)](+) complex with Xe is studied by means of quasi-classical trajectory calculations. The potential energy surface is obtained "on the fly" from AM1 semiempirical calculations, supplemented with two-body analytical potentials to model the intermolecular interactions. The simulations show that Li(+) production is the primary channel, in agreement with a previous experimental study [M. T. Rodgers and P. B. Armentrout, J. Am. Chem. Soc., 2000, 122, 8548]. Collision-induced isomerization of [Li(uracil)](+) was found to be very important as well in the 2.5-10 eV collision energy range. Three minor channels are also identified: complex formation between Xe and [Li(uracil)](+), ligand exchange to form LiXe(+), and fragmentations of the uracil ring, which are strongly nonstatistical. Additional quasi-classical trajectory calculations carried out to investigate in more detail the fragmentations of the uracil ring reveal the presence of bifurcations in the potential energy surface, as trajectories starting from a transition state give rise to four different product channels. The integral cross sections for Li(+) production calculated in this work agree well with those obtained in the experiments only for the lowest collision energies, being ∼20 times greater than the experimental values for a collision energy of 10 eV. Finally, the initial translational energy is transferred preferentially to the [Li(uracil)](+) vibrational degrees of freedom, with energy transfer to rotation being modest. The amount of energy transfer to the different degrees of freedom as a function of the collision energy follows quite nicely a model recently proposed by our group.
authors.affiliation: Departamento de Química Física and Centro Singular de Investigación en Química Biológica y Materiales Moleculares, Campus Vida, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain.
authors.forename: Roberto
authors.initials: R
authors.lastname: Rodríguez-Fernández
authors.forename: Saulo A
authors.initials: SA
authors.lastname: Vázquez
authors.forename: Emilio
authors.initials: E
authors.lastname: Martínez-Núñez
mesh_terms: D008094:Lithium / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D014498:Uracil / Q000737:chemistry*; D014978:Xenon / Q000737:chemistry
chemical_list: D009942:Organometallic Compounds; D014978:Xenon; D014498:Uracil; D008094:Lithium