# 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 NHD_{2}, from Marquardt, Sanrey, Gatti, and Lé
Quéré, ``Full-Dimensional Quantum Dynamics of Vibrationally Highly Excited NHD_{2}, *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 H_{2} on Pd(111), yielding significant differences. Is it H or H_{2} 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 CHI_{3}", *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)