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Papers by Jaime Suarez
The Journal of chemical physics, Jan 14, 2018
We describe a new approach based on semiclassical molecular dynamics that allows simulating infra... more We describe a new approach based on semiclassical molecular dynamics that allows simulating infrared absorption or emission spectra of molecular systems with inclusion of anharmonic intensities. This is achieved from semiclassical power spectra by computing first the vibrational eigenfunctions as a linear combination of harmonic states, and then the oscillator strengths associated with the vibrational transitions. We test the approach against a 1D Morse potential and apply it to the water molecule with results in excellent agreement with discrete variable representation quantum benchmarks. The method does not require any grid calculations, and it is directly extendable to high dimensional systems. The usual exponential scaling of the basis set size with the dimensionality of the system can be avoided by means of an appropriate truncation scheme. Furthermore, the approach has the advantage to provide IR spectra beyond the harmonic approximation without losing the possibility of an in...
Journal of Physical Chemistry A, 2010
Theoretical predictions and interpretations of highly excited vibrational states and their organi... more Theoretical predictions and interpretations of highly excited vibrational states and their organisation are among the most important challenges in molecular spectroscopy. In this Letter we investigate the effects of isotopic mass substitution in the well-known normal-to-local vibrational modes bifurcation of the water molecule. Considering the mass of one hydrogen atom as a second continuation parameter we calculate energy-frequency continuation/bifurcation diagrams of the principal families of periodic orbits. Extended quantum mechanical calculations reveal the localisation of the overtone eigenfunctions along the periodic orbits. The study of the changes of the phase space structures with mass variations unravel the fingerprints of bifurcations effects in the quantum states of isotopologues.
Chemical Physics, 2011
The diffuse vibrational bands, observed in the ultraviolet photodissociation spectrum of nitrous ... more The diffuse vibrational bands, observed in the ultraviolet photodissociation spectrum of nitrous oxide by exciting the molecule in the first (1)A' state, have recently been attributed to resonances localized mainly in the NN stretch and bend degrees of freedom. To further investigate the origin of this localization, fundamental families of periodic orbits emanating from several stationary points of the (1)A' potential energy surface and bifurcations of them are computed. We demonstrate that center-saddle bifurcations of periodic orbits are the main mechanism for creating stable regions in phase space that can support the partial trapping of the wave packet, and thus they explain the observed spectra. A non-linear mechanical methodology, which involves the calculation of equilibria, periodic orbits, and transition states in normal form coordinates, is applied for an in detail exploration of phase space. The fingerprints of the phase space structures in the quantum world are identified by solving the time dependent Schrödinger equation and calculating autocorrelation functions. This demonstrates that different reaction channels could be controlled if exact knowledge of the phase space structure is available to guide the initial excitation of the molecule.
The Journal of chemical physics, Jan 14, 2018
We describe a new approach based on semiclassical molecular dynamics that allows simulating infra... more We describe a new approach based on semiclassical molecular dynamics that allows simulating infrared absorption or emission spectra of molecular systems with inclusion of anharmonic intensities. This is achieved from semiclassical power spectra by computing first the vibrational eigenfunctions as a linear combination of harmonic states, and then the oscillator strengths associated with the vibrational transitions. We test the approach against a 1D Morse potential and apply it to the water molecule with results in excellent agreement with discrete variable representation quantum benchmarks. The method does not require any grid calculations, and it is directly extendable to high dimensional systems. The usual exponential scaling of the basis set size with the dimensionality of the system can be avoided by means of an appropriate truncation scheme. Furthermore, the approach has the advantage to provide IR spectra beyond the harmonic approximation without losing the possibility of an in...
Journal of Physical Chemistry A, 2010
Theoretical predictions and interpretations of highly excited vibrational states and their organi... more Theoretical predictions and interpretations of highly excited vibrational states and their organisation are among the most important challenges in molecular spectroscopy. In this Letter we investigate the effects of isotopic mass substitution in the well-known normal-to-local vibrational modes bifurcation of the water molecule. Considering the mass of one hydrogen atom as a second continuation parameter we calculate energy-frequency continuation/bifurcation diagrams of the principal families of periodic orbits. Extended quantum mechanical calculations reveal the localisation of the overtone eigenfunctions along the periodic orbits. The study of the changes of the phase space structures with mass variations unravel the fingerprints of bifurcations effects in the quantum states of isotopologues.
Chemical Physics, 2011
The diffuse vibrational bands, observed in the ultraviolet photodissociation spectrum of nitrous ... more The diffuse vibrational bands, observed in the ultraviolet photodissociation spectrum of nitrous oxide by exciting the molecule in the first (1)A' state, have recently been attributed to resonances localized mainly in the NN stretch and bend degrees of freedom. To further investigate the origin of this localization, fundamental families of periodic orbits emanating from several stationary points of the (1)A' potential energy surface and bifurcations of them are computed. We demonstrate that center-saddle bifurcations of periodic orbits are the main mechanism for creating stable regions in phase space that can support the partial trapping of the wave packet, and thus they explain the observed spectra. A non-linear mechanical methodology, which involves the calculation of equilibria, periodic orbits, and transition states in normal form coordinates, is applied for an in detail exploration of phase space. The fingerprints of the phase space structures in the quantum world are identified by solving the time dependent Schrödinger equation and calculating autocorrelation functions. This demonstrates that different reaction channels could be controlled if exact knowledge of the phase space structure is available to guide the initial excitation of the molecule.