2024
Richard Beckmann, Christoph Schran, Fabien Brieuc, Dominik Marx
Theoretical infrared spectroscopy of protonated methane isotopologues Journal Article
In: Phys. Chem. Chem. Phys., vol. 26, iss. 35, pp. 22846-22852, 2024.
Abstract | Links | BibTeX | Tags: Coupled Cluster, Quantum Dynamics, Spectra
@article{Beckmann2024/10.1039/D4CP02295E,
title = {Theoretical infrared spectroscopy of protonated methane isotopologues},
author = {Richard Beckmann and Christoph Schran and Fabien Brieuc and Dominik Marx},
url = {http://dx.doi.org/10.1039/D4CP02295E},
doi = {10.1039/D4CP02295E},
year = {2024},
date = {2024-08-13},
urldate = {2024-08-13},
journal = {Phys. Chem. Chem. Phys.},
volume = {26},
issue = {35},
pages = {22846-22852},
publisher = {The Royal Society of Chemistry},
abstract = {The vibrational spectroscopy of protonated methane and its mixed hydrogen/deuterium isotopologues remains a challenge to both experimental and computational spectroscopy due to the iconic floppiness of CH5+. Here, we compute the finite-temperature broadband infrared spectra of CH5+ and all its isotopologues, i.e. CHnD5−n+ up to CD5+, from path integral molecular dynamics in conjunction with interactions and dipoles computed consistently at CCSD(T) coupled cluster accuracy. The potential energy and dipole moment surfaces have been accurately represented in full dimensionality in terms of high-dimensional neural networks. The resulting computational efficiency allows us to establish CCSD(T) accuracy at the level of converged path integral simulations. For all six isotopologues, the computed broadband spectra compare very favorably to the available experimental broadband spectra obtained from laser induced reactions action vibrational spectroscopy. The current approach is found to consistently and significantly improve on previous calculations of these broadband vibrational spectra and defines the new cutting-edge for what has been dubbed the “enfant terrible” of molecular spectroscopy in view of its pronounced large-amplitude motion that involves all intramolecular degrees of freedom.},
keywords = {Coupled Cluster, Quantum Dynamics, Spectra},
pubstate = {published},
tppubtype = {article}
}
The vibrational spectroscopy of protonated methane and its mixed hydrogen/deuterium isotopologues remains a challenge to both experimental and computational spectroscopy due to the iconic floppiness of CH5+. Here, we compute the finite-temperature broadband infrared spectra of CH5+ and all its isotopologues, i.e. CHnD5−n+ up to CD5+, from path integral molecular dynamics in conjunction with interactions and dipoles computed consistently at CCSD(T) coupled cluster accuracy. The potential energy and dipole moment surfaces have been accurately represented in full dimensionality in terms of high-dimensional neural networks. The resulting computational efficiency allows us to establish CCSD(T) accuracy at the level of converged path integral simulations. For all six isotopologues, the computed broadband spectra compare very favorably to the available experimental broadband spectra obtained from laser induced reactions action vibrational spectroscopy. The current approach is found to consistently and significantly improve on previous calculations of these broadband vibrational spectra and defines the new cutting-edge for what has been dubbed the “enfant terrible” of molecular spectroscopy in view of its pronounced large-amplitude motion that involves all intramolecular degrees of freedom.
2023
Irén Simkó, Christoph Schran, Fabien Brieuc, Csaba Fábri, Oskar Asvany, Stephan Schlemmer, Dominik Marx, Attila G. Császár
Quantum Nuclear Delocalization and its Rovibrational Fingerprints Journal Article
In: Angewandte Chemie International Edition, vol. 62, no. 41, pp. e202306744, 2023.
Abstract | Links | BibTeX | Tags: Nuclear quantum effects, path integral molecular dynamics (PIMD), Quantum Dynamics
@article{Simko/10.1002/anie.202306744,
title = {Quantum Nuclear Delocalization and its Rovibrational Fingerprints},
author = {Irén Simkó and Christoph Schran and Fabien Brieuc and Csaba Fábri and Oskar Asvany and Stephan Schlemmer and Dominik Marx and Attila G. Császár},
url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202306744},
doi = {10.1002/anie.202306744},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {Angewandte Chemie International Edition},
volume = {62},
number = {41},
pages = {e202306744},
abstract = {Abstract Quantum mechanics dictates that nuclei must undergo some delocalization. In this work, emergence of quantum nuclear delocalization and its rovibrational fingerprints are discussed for the case of the van der Waals complex . The equilibrium structure of is planar and T-shaped, one He atom solvating the quasi-linear He−H+−He core. The dynamical structure of , in all of its bound states, is fundamentally different. As revealed by spatial distribution functions and nuclear densities, during the vibrations of the molecule the solvating He is not restricted to be in the plane defined by the instantaneously bent chomophore, but freely orbits the central proton, forming a three-dimensional torus around the chromophore. This quantum delocalization is observed for all vibrational states, the type of vibrational excitation being reflected in the topology of the nodal surfaces in the nuclear densities, showing, for example, that intramolecular bending involves excitation along the circumference of the torus.},
keywords = {Nuclear quantum effects, path integral molecular dynamics (PIMD), Quantum Dynamics},
pubstate = {published},
tppubtype = {article}
}
Abstract Quantum mechanics dictates that nuclei must undergo some delocalization. In this work, emergence of quantum nuclear delocalization and its rovibrational fingerprints are discussed for the case of the van der Waals complex . The equilibrium structure of is planar and T-shaped, one He atom solvating the quasi-linear He−H+−He core. The dynamical structure of , in all of its bound states, is fundamentally different. As revealed by spatial distribution functions and nuclear densities, during the vibrations of the molecule the solvating He is not restricted to be in the plane defined by the instantaneously bent chomophore, but freely orbits the central proton, forming a three-dimensional torus around the chromophore. This quantum delocalization is observed for all vibrational states, the type of vibrational excitation being reflected in the topology of the nodal surfaces in the nuclear densities, showing, for example, that intramolecular bending involves excitation along the circumference of the torus.
2022
Henrik R Larsson, Markus Schröder, Richard Beckmann, Fabien Brieuc, Christoph Schran, Dominik Marx, Oriol Vendrell
State-resolved infrared spectrum of the protonated water dimer: Revisiting the characteristic proton transfer doublet peak Journal Article
In: Chem. Sci., 2022, ISSN: 2041-6539.
Abstract | Links | BibTeX | Tags: Quantum Dynamics, Spectra, Water
@article{Larsson2022/10.1039/D2SC03189B,
title = {State-resolved infrared spectrum of the protonated water dimer: Revisiting the characteristic proton transfer doublet peak},
author = {Henrik R Larsson and Markus Schröder and Richard Beckmann and Fabien Brieuc and Christoph Schran and Dominik Marx and Oriol Vendrell},
doi = {10.1039/D2SC03189B},
issn = {2041-6539},
year = {2022},
date = {2022-08-01},
urldate = {2022-08-01},
journal = {Chem. Sci.},
publisher = {The Royal Society of Chemistry},
abstract = {The infrared (IR) spectra of protonated water clusters encode precise information on the dynamics and structure of the hydrated proton. However, the strong anharmonic coupling and quantum effects of these elusive species remain puzzling up to the present day. Here, we report unequivocal evidence that the interplay between the proton transfer and the water wagging motions in the protonated water dimer (Zundel ion) giving rise to the characteristic doublet peak is both more complex and more sensitive to subtle energetic changes than previously thought. In particular, hitherto overlooked low-intensity satellite peaks in the experimental spectrum are now unveiled and mechanistically assigned. Our findings rely on the comparison of IR spectra obtained using two highly accurate potential energy surfaces in conjunction with highly accurate state-resolved quantum simulations. We demonstrate that these high-accuracy simulations are important for providing definite assignments of the complex IR signals of fluxional molecules.},
keywords = {Quantum Dynamics, Spectra, Water},
pubstate = {published},
tppubtype = {article}
}
The infrared (IR) spectra of protonated water clusters encode precise information on the dynamics and structure of the hydrated proton. However, the strong anharmonic coupling and quantum effects of these elusive species remain puzzling up to the present day. Here, we report unequivocal evidence that the interplay between the proton transfer and the water wagging motions in the protonated water dimer (Zundel ion) giving rise to the characteristic doublet peak is both more complex and more sensitive to subtle energetic changes than previously thought. In particular, hitherto overlooked low-intensity satellite peaks in the experimental spectrum are now unveiled and mechanistically assigned. Our findings rely on the comparison of IR spectra obtained using two highly accurate potential energy surfaces in conjunction with highly accurate state-resolved quantum simulations. We demonstrate that these high-accuracy simulations are important for providing definite assignments of the complex IR signals of fluxional molecules.