Unimolecular reactivity of the [urea-Sr]2+ complex, a metastable dication in the gas phase: an experimental and theoretical perspective

Electron and ion spectroscopy of the cyclo-alanine-alanine dipeptide

The VUV photoionisation and photofragmentation of cyclo-alanine-alanine (cAA) has been studiedin a joint experimental and theoretical work. The photoelectron spectrum and the photoelectron-photoion coincidence (PEPICO) measurements, which enable a control...

Can Supported Reduced Vanadium Oxides form H2 from CH3OH? A Computational Gas-Phase Mechanistic Study

A detailed density functional theory study is presented to clarify the mechanistic aspects of the methanol (CH₃OH) dehydrogenation process to yield hydrogen (H₂) and formaldehyde (CH₂O). A gas-phase vanadium oxide cluster is used as a model system to represent reduced V(III) oxides supported on TiO₂ catalyst. The theoretical results provide a complete scenario, involving several reaction pathways in which different methanol adsorption sites are considered, with presence of hydride and methoxide intermediates. Methanol dissociative adsorption process is both kinetically and thermodynamically feasible on V-O-Ti and V═O sites, and it might lead to form hydride species with interesting catalytic reactivity. The formation of H₂ and CH₂O on reduced vanadium sites, V(III), is found to be more favorable than for oxidized vanadium species, V(V), taking place along energy barriers of 29.9 and 41.0 kcal/mol, respectively.

Gas-phase reactivity of [Ca(formamide)]2+ complex: an example of different dynamical behaviours

In the present contribution, we have summarized our recent work on the comprehension of [Ca(formamide)]²⁺ complex gas-phase unimolecular dissociation. By using different theoretical approaches, we were able to revise the original (and typical for such kind of problems) understanding given in terms of stationary points on the potential energy surface, which did not provide a satisfactory explanation of the experimentally observed reactivity. In particular, we point out how non-statistical and non-intrinsic reaction coordinate mechanisms are of fundamental importance.This article is part of the themed issue 'Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces'.

A RRKM study and a DFT assessment on gas-phase fragmentation of formamide-M(2+) (M = Ca, Sr)

A kinetic study of the unimolecular reactivity of formamide-M(2+) (M = Ca, Sr) systems was carried out by means of RRKM statistical theory using high-level DFT. The results predict M(2+), [M(NH2)](+) and [HCO](+) as the main products, together with an intermediate that could eventually evolve to produce [M(NH3)](2+) and CO, for high values of internal energy. In this framework, we also evaluated the influence of the external rotational energy on the reaction rate constants. In order to find a method to perform reliable electronic structure calculations for formamide-M(2+) (M = Ca, Sr) at a relatively low computational cost, an assessment of different methods was performed. In the first assessment twenty-one functionals, belonging to different DFT categories, and an MP2 wave function method using a small basis set were evaluated. CCSD(T)/cc-pWCVTZ single point calculations were used as reference. A second assessment has been performed on geometries and energies. We found BLYP/6-31G(d) and G96LYP/6-31+G(d,p) as the best performing methods, for formamide-Ca(2+) and formamide-Sr(2+), respectively. Furthermore, a detailed assessment was done on RRKM reactivity and G96LYP/6-31G(d) provided results in agreement with higher level calculations. The combination of geometrical, energetics and kinetics (RRKM) criteria to evaluate DFT functionals is rather unusual and provides an original assessment procedure. Overall, we suggest using G96LYP as the best performing functional with a small basis set for both systems.