Amaia Saracibar

A comparison of the quantum state-specific efficiency of N + N2 reaction computed on different potential energy surfaces.

State-to-state exact quantum probabilities of the N + N2 exchange reaction have been calculated on the recently proposed L4 potential energy surface fitted to high level ab initio points using full-dimensional time-independent quantum techniques. Thermal rate coefficient values calculated on L4 were found not to differ from those calculated on a previously proposed potential energy surface. On the contrary, state-specific reaction probabilities calculated on the two surfaces are shown to differ significantly. Arguments for attributing the difference to specific features of the considered potential energy surfaces are provided.

An extension of the molecular simulator GEMS to calculate the signal of crossed beam experiments

By exploiting the potentialities of collaborative work and of high throughput computing on the grid platform recently deployed within the European Grid Initiative and made available to the virtual organization COMPCHEM, it has been possible to extend GEMS, a simulator of molecular systems, to reproduce in an ab initio fashion the signal measured in molecular beam experiments. As a case study the crossed beam experiment measuring the differential cross section of the OH(vOH = 0, jOH = 0) + CO(vCO = 0, jCO = 0) → H + CO2 reaction has been considered. The results of the calculations provide a univocal evaluation of the accuracy of the ab initio potential energy surfaces proposed in the literature.

Calculated versus measured product distributions of the OH+D2 reaction

Product distributions of the OH+D2→HOD+D reaction, calculated using quasi-classical means, on various potential energy surfaces for the rotational states j D 2=0, 1, 2, 3 and 4 of the D2 molecule are compared with those derived from crossed molecular beam experiments with the aim of assessing the validity of the proposed potential energy functionals in describing the reaction channel of the system. Surprisingly, the most accurate surface, while leading to an excellent reproduction of translational and angular product distributions, was found to be unable to reproduce the measured vibrational distribution.

Effect of the total angular momentum on the dynamics of the H2 + H2 system.

Extended full-dimensional quasiclassical trajectory calculations have been performed for the H(a)H(b) (v(ab) = 10, 11, 12, 13, 14, j(ab) = 0) + H(c)H(d) (v(cd) = 0, j(cd) = 0) collisions at values of the translational energy ranging from threshold to 1.5 eV and values of the total angular momentum quantum number J varying from zero to very large ones. Collision-induced dissociation, four-center exchange reaction, and single exchange process probabilities have been calculated. Full-dimensional classical calculations were found to reproduce well the corresponding (J = 0) quantum results, including the thresholds. In contrast, the agreement of full-dimensional classical calculations with the corresponding both quantum and classical reduced dimensionality ones was found to be poor. The effect of varying J on the efficiency of the various processes has also been investigated. Four-center reactions were found to be favored by low values of J, whereas dissociation processes were found to be favored by higher values of J, as expected from the fact that energy exchange takes place at longer range than mass exchange. To evaluate to what extent the J = 0 full-dimensional calculations represent the unconstrained dynamics of the system, J-shift model classical results were compared with the all-J ones. Product vibrational distributions for both partially dissociative and exchange processes were also found to depend significantly on the value of J.

Grid Computing in Time-Dependent Quantum Reactive Dynamics

A study of the dependence of the cross section on the rotational energy for the N + N 2 reaction is presented. Cross sections have been calculated using a time-dependent quantum method and applying the centrifugal sudden approximation. This approximation decouples the projections of the total angular momentum and therefore breaks the calculations into several thousand runs suitable for distribution on a computing Grid. In order to handle this computational burden a procedure managing the submission of jobs and the subsequent retrieval of results has been designed. The procedure has been implemented on the EGEE production Grid and the related performance has been measured.

Quantum Mechanical Capture/Phase Space Theory Calculation of the Rate Constants for the Complex-Forming CH + H2 Reaction

Six-dimensional wave packet calculations on an accurate potential energy surface are used to obtain the quantum mechanical capture (QM C) probabilities for CH + H(2) corresponding to a variety of total angular momenta and internal reactant states. Rate constant calculations are made feasible by employing a Monte Carlo based sampling procedure. The QM C probabilities alone are also used to estimate the high pressure CH + H(2) rate constants corresponding to stabilization or CH(3) formation. The rate constants for CH + H(2) --> CH(2) + H reaction in the low pressure limit are obtained by combining the QM C probabilities with a phase space theory (PST) approximation for product formation from the complex. Our results are compared with the experimental results of Brownsword et al. (J. Chem. Phys. 1997, 106, 7662), as well as with purely classical PST calculations. The QM C probabilities are shown to be highly dependent on the initial rotational states of the reactants corresponding to orientational restrictions on complex formation. Consistent with this, our QM C high pressure rate constants for CH(3) formation are lower than the purely classical PST rate constants. These QM C rate constants also are in reasonable accord with experiment. A similar but somewhat more subtle picture emerges regarding the QM C/PST rate constants for CH(2) + H formation.

Capture and dissociation in the complex-forming CH(v = 0,1) + D2 → CHD + D, CD2 + H, CD + HD reactions and comparison with CH(v = 0,1) + H2

Rate coefficients for the CH(v = 0,1) + D(2) reaction have been determined for all possible channels (T: 200-1200 K), using the quasiclassical trajectory method and a suitable treatment of the zero point energy. Calculations have also been performed on the CH(v = 1) + H(2) reaction and the CH(v = 1) + D(2) → CH(v = 0) + D(2) process. Most of the results can be understood considering the key role played by the deep minimum of the potential energy surface (PES), the barrierless character of the PES, the energy of the reaction channels, and the kinematics. The good agreement found between theory and experiment for the rate coefficients of the capture process of CH(v = 0) + D(2), the total reactivity of CH(v = 1) + D(2), H(2), as well as the good agreement observed for the related CH(v = 0) + H(2) system (capture and abstraction), gives confidence on the theoretical rate coefficients obtained for the capture processes of CH(v = 1) + D(2), H(2), the individual reactive processes of CH(v = 1) + D(2), H(2), the abstraction and abstraction-exchange reactions for CH(v = 0) + D(2), and the inelastic process mentioned above, for which there are no experimental data available, and that can be useful in combustion chemistry and astrochemistry.

Cross-curricular skills development in final-year dissertation by active and collaborative methodologies

ABSTRACT European Frame for Higher Education has led universities to adapt their teaching schemes. Degrees must train students in competences including specific and cross-curricular skills. Nevertheless, there are important limitations to follow skill improvement through the consecutive academic years. Final-year dissertation (FYD) offers the opportunity to assess these aspects so linked to the professional requirements. The experience reported here offers an alternative methodology for the FYD in order to reinforce cross-curricular skills and substitute the classic final evaluation schemes. A new protocol for the FYD was defined and tested in the Degree in Human Nutrition and Dietetics, with the participation of students and lecturers from different disciplines. The new methodology included collaborative activities that required students active implication and participation. New cross-curricular skills not considered before were included and evaluated in a continuous way: analysis and critical attitude, as well as team working. Obtained data revealed an improvement over cross-curricular skills. Student–student cooperation resulted in significant contributions to enhance FYD quality. The new methodology was satisfactorily valued by students. The main keys for the successful implementation of this protocol were the followings: encouragement of teachers and students, coordination, information and communication technologies, and clear guidelines.