Periodic bond breaking and making in the electronic ground state on a sub-picosecond timescale: OH bending spectroscopy of malonaldehyde in the frequency domain at low temperature

Lüttschwager, Nils Olaf Bernd; Wassermann, Tobias N.; Coussan, S.; Suhm, Martin A.

doi:10.1039/c002345k

Cited by 38 publications

(39 citation statements)

References 37 publications

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“…For the spontaneous Raman scattering experiment 21,41,42 (Fig. 2), the expansion zone is crossed by a mildly focussed 18 W single mode 532 nm laser (Coherent) about 1 mm downstream a 4 Â 0.15 mm 2 stainless steel slit nozzle opening to a mechanically pumped vacuum chamber.…”

Section: Experimental Techniquesmentioning

confidence: 99%

Stretching and folding of 2-nanometer hydrocarbon rods

Lüttschwager

Suhm

2014

Soft Matter

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Linear alkanes CnH2n+2 in vacuum isolation are finite models for an infinite polyethylene chain. Using spontaneous Raman scattering in supersonic jet expansions for n = 13-21 in different spectral ranges, we determine the minimal chain length nh for the cohesion-driven folding of the preferred extended all-trans conformation into a hairpin structure. We treat fully stretched all-trans alkanes as molecular "nanorods" and derive Young's modulus E for the stretching of an isolated single-strand polyethylene fibre by extrapolating the longitudinal acoustic mode to infinite chain length. Two key quality parameters for accurate intra- and intermolecular force fields of hydrocarbons (nh = 18 ± 1, E = 305 ± 5 GPa) are thus derived with high accuracy from experimental spectroscopy.

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Section: Experimental Techniquesmentioning

confidence: 99%

Stretching and folding of 2-nanometer hydrocarbon rods

Lüttschwager

Suhm

2014

Soft Matter

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“…For MA, the infrared (IR) spectrum [10][11][12][13] and the ground state tunneling splitting [14][15][16] for hydrogen transfer have been determined experimentally. Calculations at different levels of theory have also been carried out to assign these spectra and to reproduce the splitting.…”

Section: Introductionmentioning

confidence: 99%

Reactive dynamics and spectroscopy of hydrogen transfer from neural network-based reactive potential energy surfaces

2020

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The "in silico" exploration of chemical, physical and biological systems requires accurate and efficient energy functions to follow their nuclear dynamics at a molecular and atomistic level. Recently, machine learning tools gained a lot of attention in the field of molecular sciences and simulations and are increasingly used to investigate the dynamics of such systems. Among the various approaches, artificial neural networks (NNs) are one promising tool to learn a representation of potential energy surfaces. This is done by formulating the problem as a mapping from a set of atomic positions x and nuclear charges Z i to a potential energy V (x). Here, a fully-dimensional, reactive neural network representation for malonaldehyde (MA), acetoacetaldehyde (AAA) and acetylacetone (AcAc) is learned. It is used to run finite-temperature molecular dynamics simulations, and to determine the infrared spectra and the hydrogen transfer rates for the three molecules. The finite-temperature infrared spectrum for MA based on the NN learned on MP2 reference data provides a realistic representation of the lowfrequency modes and the H-transfer band whereas the CH vibrations are somewhat too high in frequency. For AAA it is demonstrated that the IR spectroscopy is sensitive to the position of the transferring hydrogen at either the OCH-or OCCH 3 end of the molecule. For the hydrogen transfer rates it is demonstrated that the O-O vibration (at ∼ 250 cm −1 ) is a gating mode and largely determines the rate at which the hydrogen is transferred between the donor and acceptor. Finally, possibilities to further improve such NN-based potential energy surfaces are explored. They include the transferability of an NN-learned energy function across chemical species (here methylation) and transfer learning from a lower level of reference data (MP2) to a higher level of theory (pair natural orbital-LCCSD(T)).

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“…Very recently, Suhm and coworkers reported these effects experimentally in a combined FTIR and Raman study for twelve vibrational fundamentals, 1 greatly extending their earlier work for four fundamentals. 2,3 Comparisons were made with previous calculations, and, with the exception of recent multi-configuration time-dependent Hartree (MCTDH) calculations of Hammer and Manthe, 4 who used the accurate full-dimensional potential energy surface of Wang et al, 5 the agreement was not very good. Those calculations are at the state-of-the-art, but were not fully converged for a number of states and also did not extend to all the fundamentals.…”

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confidence: 99%

Mode-specific tunneling using the Qim path: Theory and an application to full-dimensional malonaldehyde

Wang

Bowman²

2013

The Journal of Chemical Physics

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We present a theory of mode-specific tunneling that makes use of the general tunneling path along the imaginary-frequency normal mode of the saddle point, Qim, and the associated relaxed potential, V(Qim) [Y. Wang and J. M. Bowman, J. Chem. Phys. 129, 121103 (2008)]. The novel aspect of the theory is the projection of the normal modes of a minimum onto the Qim path and the determination of turning points on V(Qim). From that projection, the change in tunneling upon mode excitation can be calculated. If the projection is zero, no enhancement of tunneling is predicted. In that case vibrationally adiabatic (VA) theory could apply. However, if the projection is large then VA theory is not applicable. The approach is applied to mode-specific tunneling in full-dimensional malonaldehyde, using an accurate full-dimensional potential energy surface. Results are in semi-quantitative agreement with experiment for modes that show large enhancement of the tunneling, relative to the ground state tunneling splitting. For the six out-of-plane modes, which have zero projection on the planar Qim path, VA theory does apply, and results from that theory agree qualitatively and even semi-quantitatively with experiment. We also verify the failure of simple VA theory for modes that show large enhancement of tunneling.

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Periodic bond breaking and making in the electronic ground state on a sub-picosecond timescale: OH bending spectroscopy of malonaldehyde in the frequency domain at low temperature

Cited by 38 publications

References 37 publications

Stretching and folding of 2-nanometer hydrocarbon rods

Stretching and folding of 2-nanometer hydrocarbon rods

Reactive dynamics and spectroscopy of hydrogen transfer from neural network-based reactive potential energy surfaces

Mode-specific tunneling using the Qim path: Theory and an application to full-dimensional malonaldehyde

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