Enric Bosch

Bidimensional tunneling dynamics of malonaldehyde and hydrogenoxalate anion. A comparative study

One‐dimensional and bidimensional tunneling splittings have been calculated in malonaldehyde (MA) and hydrogenoxalate anion (HX) systems. Two different monodimensional paths have been considered: the intrinsic reaction path (IRP) and the linear reaction path (LRP). A bidimensional model that includes the coupling between the proton transfer motion and the vibration of the heavy atoms is then used. We find that with the bidimensional model the splittings are 2 orders of magnitude greater than the monodimensional ones, and close to the previous experimental and theoretical values for the MA when zero point energy is introduced. At all levels of calculation we obtain that the splitting is greater in the MA than in the HX. This fact is attributed to the different size of the rings through which the proton transfer occurs.

A semiclassical simulation for tunneling dynamics of malonaldehyde and hydrogenoxalate anion

Abstract A semiclassical tunneling methodology has been adopted in order to comparatively analyze the tunneling splitting of malonaldehyde and hydrogenoxalate anion. This method proves to be very suitable to be applied to these systems. Analysis of the results allows a deeper understanding of the chemical difference of both systems. A clear dependence of the splitting on the ring size within which the intramolecular proton transfer takes place is found in agreement with our previous results.

Intrinsic reaction coordinate calculations for reaction paths possessing branching points

Abstract A 3-21+G energy surface corresponding to the proton transfer reaction in the hydroperoxyl anion solvated by one water molecule presents interesting topological features. In particular the intrinsic reaction coordinate that begins at the transition state does not lead to a minimum but to a saddle point of second order passing through two branching points. A new strategy to obtain the true reaction path in these cases is proposed.

Comparison between intramolecular proton transfers involving the carboxylate and alkoxide groups

We have studied the intramolecular proton transfer in the hydroxyacetate, hydrogenoxalate and glycolate anions by means of ab initio calculations. Due to the higher proton affinity of RO− as compared to R-COO−, there is only one minimum in the hydroxyacetate potential surface. Conversely, given that hydrogenoxalate and glycolate anions are symmetric systems, a transition state appears in both cases. The greater barrier in the hydrogenoxalate with respect to the glycolate anion can be attributed to the reorganisation energy of the substrate. The proton motion in the hydrogenoxalate molecule is clearly coupled to the motion of the other atoms.

Ab initio study on the effect of attaching a hydrogen molecule to the (H5O2)+ ion cluster

Ab initio energy calculations using the Mo/ller–Plesset perturbation theory up to fourth order with the 6‐31G(D,P) basis set have been performed for the H5O2+ ion cluster with and without a hydrogen molecule attached to it. In agreement with experimental results, a C2 structure which gives rise to only two high O–H stretching frequencies is predicted to be the only minimum of the isolated ion, whereas when H2 is present, again only one minimum is found which can be roughly assigned to be of the Cs type. This structure is predicted to have four active O–H stretching frequencies, again in agreement with the experimental spectrum.

The use of optimized tunneling paths within a model based on classical trajectories

Abstract A semi-classical tunneling methodology combined with the use of classical trajectories is adopted in order to evaluate the tunneling splittings for bi-dimensional surfaces of malonaldehyde and hydrogenoxalate anion proton transfer reactions. It is shown that the optimization of the tunneling path may lead to an important improvement of the results while representing a negligible increment of computation time as compared with the use of straight-line tunneling paths.