Exploring Expansions of the Potential and Dipole Surfaces Used for Vibrational Perturbation Theory

McCoy, Anne B.; Boyer, Mark A.

doi:10.1021/acs.jpca.2c05792

Cited by 11 publications

(8 citation statements)

References 41 publications

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“…From a computational point of view, clusters are small enough to be accessible with accurate electronic structure methods. They also might allow an explicit treatment of anharmonic effects, − multibody interactions, and quantum nuclear effects ,, without recourse to methods that make uncontrolled approximations, like path-integral molecular dynamics.…”

Section: Introductionmentioning

confidence: 99%

Water–Hydrocarbon Interactions in Anionic Pyrene Monohydrate

LeMessurier,

Salzmann,

Leversee

et al. 2024

J. Phys. Chem. B

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Interactions between water and polycyclic aromatic hydrocarbons are essential in many aspects of chemistry, from interstellar and atmospheric processes to interfacial hydrophobicity and wetting phenomena. Despite their growing importance, the intermolecular potentials of the water−hydrocarbon interactions are underdeveloped compared to the water−water potentials, and there are similarly few experimental probes that are sensitive to the details of the water−hydrocarbon potential. We present a combined experimental and computational study of anionic pyrene monohydrate, one of the simplest water/hydrocarbon clusters. The action spectrum in the OH region of the mass-selected cluster ion provides a rigorous benchmark for intermolecular potentials and computational methodologies. We identify missing intermolecular interactions and shortcomings in conventional dynamics calculations by comparing experimental data to density functional theory and classical molecular dynamics calculations. Kinetic trapping is prevalent, even for one water molecule and one pyrene molecule, leading to slow equilibration in conventional molecular dynamics calculations, even on nanosecond time scales and at low temperatures (50 K). At constant energy, temperature fluctuations for the pair of molecules are substantial. Immersing the system in a bath of soft spheres and employing parallel tempering alleviates kinetic trapping and dampens temperature fluctuations, bringing the system closer to the thermodynamic limit. With such augmented sampling, a simple, flexible water model reproduces the line width and the asymmetric broadening of the symmetric OH stretching mode, which we assign to spectral diffusion. In the OH stretching region, dynamics calculations predict a more intense antisymmetric peak than experiments observe but do not predict the bimodal split symmetric peak that the experiments show. Our work suggests that electronic polarization, missing in the empirical force field, is responsible for the first discrepancy and that quantum nuclear effects, captured neither in density functional theory nor in classical dynamics, may be responsible for the second.

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Section: Introductionmentioning

confidence: 99%

Water–Hydrocarbon Interactions in Anionic Pyrene Monohydrate

LeMessurier,

Salzmann,

Leversee

et al. 2024

J. Phys. Chem. B

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“…As implemented in the Gaussian program package, these expansions are obtained by displacing the equilibrium geometry of the complex of interest along each of the normal mode coordinates. This information allows for the evaluation of the third and fourth derivatives of the potential as well as second and third derivatives of the dipole surface using finite difference schemes. − …”

Section: Methodsmentioning

confidence: 99%

Probing Ion–Receptor Interactions in Halide Complexes of Octamethyl Calix[4]Pyrrole

Terry,

Foreman,

Rasmussen

et al. 2024

J. Am. Chem. Soc.

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Ion receptors are molecular hosts that bind ionic guests, often with great selectivity. The interplay of solvation and ion binding in anion host−guest complexes in solution governs the binding efficiency and selectivity of such ion receptors. To gain molecular-level insight into the intrinsic binding properties of octamethyl calix[4]pyrrole (omC4P) host molecules with halide guest ions, we performed cryogenic ion vibrational spectroscopy (CIVS) of omC4P in complexes with fluoride, chloride, and bromide ions. We interpret the spectra using density functional theory, describing the infrared spectra of these complexes with both harmonic and anharmonic second-order vibrational perturbation theory (VPT2) calculations. The NH stretching modes of the pyrrole moieties serve as sensitive probes of the ion binding properties, as their frequencies encode the ion−receptor interactions. While scaled harmonic spectra reproduce the experimental NH stretching modes of the chloride and bromide complexes in broad strokes, the high proton affinity of fluoride introduces strong anharmonic effects. As a result, the spectrum of F − •omC4P is not even qualitatively captured by harmonic calculations, but it is recovered very well by VPT2 calculations. In addition, the VPT2 calculations recover the intricate coupling of the NH stretching modes with overtones and combination bands of CH stretching and NH bending modes and with low-frequency vibrations of the omC4P macrocycle, which are apparent for all of the halide ion complexes investigated here. A comparison of the CIVS spectra with infrared spectra of solutions of the same ion−receptor complexes in d 3 -acetonitrile and d 6acetone shows how ion solvation changes the ion−receptor interactions for the different halide ions.

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“…As described in the Supporting Information, we believe that the origin of the large intensities of symmetry-forbidden transitions predicted by the VPT2 calculations most likely reflects numerical instabilities in the evaluation of the fourth derivatives of the potential, particularly for out-of-plane vibrations. These derivatives are obtained through finite difference schemes where the fourth derivatives are obtained by numerical evaluation of the elements of the Hessian in terms of the normal mode coordinates. − Analysis of the quartic contributions shows that there are a number of such terms, which couple states of different symmetries and have values that approach several cm –1 . While these terms will have a negligible effect on the energies, they will contribute to the second-order correction to the wave functions and, through this, lead to the problematic intensities that are noted above (see Supporting Information).…”

Section: Methodsmentioning

confidence: 99%

Infrared Spectrum of the Pyrene Anion in the CH Stretching Region

Salzmann,

McCoy,

Weber

2024

J. Phys. Chem. A

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In this work, we report the infrared spectrum of the pyrene anion, measured using messenger tagging with up to three Ar atoms. We assign the spectrum using density functional theory and vibrational perturbation theory. We discuss our results in the context of computed and experimental spectra from the literature as well as recent observations from astronomical sources, addressing the question of whether polycyclic aromatic hydrocarbon anions could contribute to the strong infrared emission bands at 3.29 μm from carbon-rich regions of space.

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Exploring Expansions of the Potential and Dipole Surfaces Used for Vibrational Perturbation Theory

Cited by 11 publications

References 41 publications

Water–Hydrocarbon Interactions in Anionic Pyrene Monohydrate

Water–Hydrocarbon Interactions in Anionic Pyrene Monohydrate

Probing Ion–Receptor Interactions in Halide Complexes of Octamethyl Calix[4]Pyrrole

Infrared Spectrum of the Pyrene Anion in the CH Stretching Region

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