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Roberto MARQUARDT - Research interests

Roberto Marquardt's research interests are in the field of molecular quantum dynamics, in particular the dynamics of highly excited vibrational states and high resolution spectroscopy of small molecular compounds. The following examples are representative of the main research lines.

The investigation of the molecular quantum dynamics and interpretation of data from time dependent spectroscopic studies through the calculation of wave packet motion in configuration space; the figure shows contour lines of the probability density for finding planar ammonia molecules after infrared excitation of the NH stretching vibration in NHD2, from Marquardt, Sanrey, Gatti, and Lé Quéré, ``Full-Dimensional Quantum Dynamics of Vibrationally Highly Excited NHD2, J. Chem. Phys. 133, 174302 (2010)

The modeling of multidimensional, global potential energy surfaces (PES) and surfaces of the vector valued electric dipole moment; the figure shows two different stereomutation pathways from a compact and global analytical representation of the PES of methane, from Marquardt and Quack, ``Global Analytical Potential Hypersurfaces for large Amplitude Motion and Reactions in Methane. II. Characteristic Properties of the Potential and Comparison to Other Potentials and Experimental Information'', J. Phys. Chem. A 108, 3166-3181 (2004)

The study of physisorption and chemisorption processes occurring on metallic surfaces, and the quantum dynamics of the diffusion of adsorbed molecules. Heterogeneous catalysis is an essential process for the world's economy and its sustainable growth. While progress has been made in the past decades to its understanding, many elementary steps remain unresolved. One very important step is the diffusion of the chemically reacting adsorbates on the catalytic substrate. The nature of this elementary step has been unraveled since more than 10 years by high resolution 3He-spin-echo experiments. The interpretation of these experiments remains controversial. For instance, the barrier for diffusion of CO on a copper surface is predicted to be three times higher along the <110> direction than along the <100> direction, as indicated in the figure below (adapted from Marquardt et al., J. Chem. Phys. 132, 074108 (2010)), whereas the spin echo experiments seem to indicate that the barriers should be similar (Alexandrowicz et al. Phys. Rev. Lett. 93, 156103 (2004)).

In a more recent work (Firmino et al. J. Phys. Chem. Lett. 5, 4270 (2014)) insight into the experimental outcome was gained from first principle calculations, for the very first time, showing that quantum effects are important above room temperature. The theory developed in that work allowed us for instance to calculate diffusion rates for H and H2 on Pd(111), yielding significant differences. Is it H or H2 that is being monitored in the experiments? The answer to this question is not obvious at all and is one topic of current investigation.

The solution of the Schrödinger equation for the vibrational-rotational problem of polyatomic molecules (time dependent and time independent) in configuration space; the figure shows contour lines of the probability densities of highly excited vibrational states of the water monomer at total angular momentum J=0, having each 5 quanta of OH stretching vibrations (symmetric (A) and antisymmetric (B)), from a discrete variable representation of the Hamiltonian in Radau coordinates (given as the axes of the figures in units of 100 pm), from Cornaton, Krishna and Marquardt, Mol. Phys. (2013)

The determination and interpretation of data from high resolution rovibrational spectroscopy, mainly in overtone regions; the figure shows a detail of the overtone spectrum in iodoform, from Marquardt, Golçalves and Sala, ``Overtone Spectrum of the CH Chromophore in CHI3", J. Chem. Phys. 103, 8391-8403 (1995)

The determination of potential energy surfaces for the nuclear motion in molecules from first principle calculations; the figure shows potential energy functions for severalm electronic states of the copper nitrosyl system, from Krishna and Marquardt, ``Ab initio calculations of the lowest electronic states in the CuNO system'', J. Chem. Phys. 136, 244303 (2012)

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