Force dependence of the infrared spectra of polypropylene calculated with density functional theory

Pill, Michael F.; Kersch, Alfred; Clausen‐Schaumann, Hauke; Beyer, Martin K.

doi:10.1016/j.polymdegradstab.2016.03.025

Cited by 10 publications

(18 citation statements)

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“…The influence of an external force on the molecular structure of a polymer can be followed by recording infrared spectra [ 16 – 29 ]. External force modifies the force constants of vibrational modes [ 30 ]. Since structural deformation changes the charge distribution in the molecule, the transition dipole moment and thus the infrared intensity is influenced as well [ 30 ], resulting in the observed force-dependent shift of the infrared bands and changes in the intensity.…”

Section: Introductionmentioning

confidence: 99%

Theoretical simulation of the infrared signature of mechanically stressed polymer solids

Sammon¹,

Ončák²,

Beyer³

2017

Beilstein J. Org. Chem.

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Mechanical stress leads to deformation of strands in polymer solids, including elongation of covalent bonds and widening of bond angles, which changes the infrared spectrum. Here, the infrared spectrum of solid polymer samples exposed to mechanical stress is simulated by density functional theory calculations. Mechanical stress is described with the external force explicitly included (EFEI) method. The uneven distribution of the external stress on individual polymer strands is accounted for by a convolution of simulated spectra with a realistic force distribution. N-Propylpropanamide and propyl propanoate are chosen as model molecules for polyamide and polyester, respectively. The effect of a specific force on the polymer backbone is a redshift of vibrational modes involving the C–N and C–O bonds in the backbone, while the free C–O stretching mode perpendicular to the backbone is largely unaffected. The convolution with a realistic force distribution shows that the dominant effect on the strongest infrared bands is not a shift of the peak position, but rather peak broadening and a characteristic change in the relative intensities of the strongest bands, which may serve for the identification and quantification of mechanical stress in polymer solids.

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Section: Introductionmentioning

confidence: 99%

Theoretical simulation of the infrared signature of mechanically stressed polymer solids

Sammon¹,

Ončák²,

Beyer³

2017

Beilstein J. Org. Chem.

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“…Spin-flip at high pressures can be attributed to the increase in splitting of the 3d levels at the metal site such that the potential energy required to maintain a high spin configuration surpasses the spin pairing energy. Examples include shifts of signals in infrared [16][17][18] and optical spectra, [18][19][20] as well as changes in reaction kinetics. We find the pressure required for spin transition to be a function of ligand position in the spectrochemical sequence [10] and demonstrate that the spin transition pressure can be tuned by an adequate choice of the ligand field.…”

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confidence: 99%

“…[12] Optimal molecular geometries under external forces can be computed with an assortment of techniques that yield a force-modified potential energy surface (FMPES). Examples include shifts of signals in infrared [16][17][18] and optical spectra, [18][19][20] as well as changes in reaction kinetics. Examples include shifts of signals in infrared [16][17][18] and optical spectra, [18][19][20] as well as changes in reaction kinetics.…”

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confidence: 99%

“…[13][14][15] These techniques quantify the change in the molecular PES under external stresses and the resulting changes in observables. Examples include shifts of signals in infrared [16][17][18] and optical spectra, [18][19][20] as well as changes in reaction kinetics. [21,22] Spatially varying nuclear forces have been described in a previous work as a generalized force-modified potential energy surface (G-FMPES).…”

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Quantum Chemical Modeling of Pressure‐Induced Spin Crossover in Octahedral Metal‐Ligand Complexes

2019

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Spin state switching on external stimuli is a phenomenon with wide applicability, ranging from molecular electronics to gas activation in nanoporous frameworks. Here, we model the spin crossover as a function of the hydrostatic pressure in octahedrally coordinated transition metal centers by applying a field of effective nuclear forces that compress the molecule towards its centroid. For spin crossover in first-row transition metals coordinated by hydrogen, nitrogen, and carbon monoxide, we find the pressure required for spin transition to be a function of the ligand position in the spectrochemical sequence. While pressures on the order of 1 GPa are required to flip spins in homogeneously ligated octahedral sites, we demonstrate a fivefold decrease in spin transition pressure for the archetypal strong field ligand carbon monoxide in octahedrally coordinated Fe 2 + in [Fe(II)(NH 3 ) 5 CO] 2 + .Pressure-induced spin-flips of transition metal sites involve changes in Coulomb energy, closed shell repulsions, covalent bonding energy and crystal field energy. [1,2] Using the computational Extreme-Pressure PCM (XP-PCM) protocol, [3][4][5] it has been shown that high pressures cause drastic electronic rearrangements, causing first row transition metals with electronic configurations d n (4 � n � 8) to favor low spin configurations at high pressures. [6] In a metal-organic framework (MOF) with exposed Fe(II) sites, a distinct step as a function of atmospheric pressure has been observed in the adsorption isotherm of carbon monoxide, for which a cooperative spin-transition mechanism involving interacting iron centers in the MOF on introduction of the strong-field ligand carbon monoxide has been proposed. [7] In general, the use of MOFs in the separation of industrially relevant gases like hydrogen, nitrogen and carbon monoxide holds a lot of promise, due to the large surface areas, the thermal stability and the adjustability of various parameters of the MOFs. [8] The smallest building block of spin crossover systems is often an octahedrally coordinated transition metal center with its 3d orbitals split by the ligand field environment. Spin-flip at high pressures can be attributed to the increase in splitting of the 3d levels at the metal site such that the potential energy required to maintain a high spin configuration surpasses the spin pairing energy. [9] Using effective nuclear forces scaled by their distances from the molecular centroid we here model spin crossover in octahedral metal-ligand complexes as a function of hydrostatic pressure. We find the pressure required for spin transition to be a function of ligand position in the spectrochemical sequence [10] and demonstrate that the spin transition pressure can be tuned by an adequate choice of the ligand field. Finer quantum chemical effects at play in the process involve a change in the covalent binding energy, Pauli repulsion, and charge transfer as a function of pressure, as demonstrated with an Energy Decomposition Analysis (EDA) [11] scheme.Any external force on...

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Quantum Chemical Modeling of Pressure-Induced Spin Crossover in Octahedral Metal-Ligand Complexes

Stauch

Chakraborty²,

Head‐Gordon³

2019

Preprint

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Spin state switching on external stimuli is a phenomenon with wide applicability ranging from molecular electronics to gas activation in nanoporous frameworks. Here we model spin crossover as a function of hydrostatic pressure in octahedrally coordinated transition metal centers by applying a field of effective nuclear forces that compress the molecule towards its centroid. For spin crossover in first-row transition metals coordinated by hydrogen, nitrogen, and carbon monoxide, we find the pressure required for spin transition to be a function of ligand position in the spectrochemical sequence. While pressures on the order of 1 GPa are required to flip spins in homogeneously ligated octahedral sites, we demonstrate a five-fold decrease in spin transition pressure for the archetypal strong field ligand carbon monoxide in octahedrally coordinated Fe2+ in [Fe(II)(NH3)5CO]2+.

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Force dependence of the infrared spectra of polypropylene calculated with density functional theory

Cited by 10 publications

References 71 publications

Theoretical simulation of the infrared signature of mechanically stressed polymer solids

Theoretical simulation of the infrared signature of mechanically stressed polymer solids

Quantum Chemical Modeling of Pressure‐Induced Spin Crossover in Octahedral Metal‐Ligand Complexes

Quantum Chemical Modeling of Pressure-Induced Spin Crossover in Octahedral Metal-Ligand Complexes

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