Linear and Helical Carbonic Acid Clusters

Wallace, Austin M.; Fortenberry, Ryan C.

doi:10.1021/acs.jpca.1c02878

Cited by 3 publications

(27 citation statements)

References 35 publications

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“…The antianti conformational isomer is substantially higher in energy at 0.49 eV higher than the syn-syn isomer. 20,28 Furthermore, computational and experimental investigations into the βcarbonic acid polymorph support the idea that the structure is composed of syn-syn carbonic acid monomers linked together in a ribbon structure. 20,27−29 In the UV region, β-carbonic acid is characterized by a single major peak at 8.92 eV (139 nm).…”

Section: ■ Introductionmentioning

confidence: 89%

“…This factor is produced for each cluster from relative energies to mimic the relative abundances of each cluster's contribution in an amorphous solid ice. By approximation of all the binding energy turning into the thermal energy, the temperature for calculating the Boltzmann factor comes from the binding energy of the lowest energy dimer (0.80 eV), 20 yielding 9259 K. The full set of scaled excitations are input into a Gaussian line shape procedure with a full width at half-maximum height of 0.5 eV, which constructs a normalized artificial UV spectrum. Again, a similar procedure has been shown to reproduce the UV experimental spectrum of amorphous ammonia, carbon dioxide, and water in a semiquantitative fashion such that unique interpretation of the experimental results based on the theoretical results is possible.…”

Section: ■ Computational Methodsmentioning

confidence: 99%

“…The linear octamer ribbon structure is the extended structure from previous work that appears to correspond with β-carbonic acid. 20,27 This octamer is optimized with…”

Section: ■ Computational Methodsmentioning

confidence: 99%

“…19,22−26 Meanwhile, β-carbonic acid can be produced from the irradiation of CO 2 :H 2 O ice mixtures raised to the temperature of 220 K. 6,8 Previous computational work has demonstrated that the lowest energy isomer of the carbonic acid monomers is the synsyn conformation with the hydrogens both pointing toward the ketone oxygena unit of β-carbonic acid. 20,27 This monomer is followed closely in relative energy by the syn-anti conformational isomer at 0.08 eV higher in energy. The antianti conformational isomer is substantially higher in energy at 0.49 eV higher than the syn-syn isomer.…”

Section: ■ Introductionmentioning

confidence: 94%

“…31 Such a procedure is related to ongoing research in polymolecular quantum chemistry, 32,33 and this represents an extension to amorphous solids of astrophysical application. 20,31 Therefore, the present work will utilize this procedure to analyze amorphous carbonic acid clusters' UV spectra to potentially characterize the unknown carbonic acid structure observed in Experimental Solid A. 8 Additionally, the ribbon structure is investigated further with respect to the Experimental Solid B spectrum, and a new twisted motif for pairs of dimers is also explored to see its relevance to either case.…”

Section: ■ Introductionmentioning

confidence: 99%

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Theoretical Characterization of Carbonic Acid Clusters in the UV

Wallace

Fortenberry

2022

J. Phys. Chem. A

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Two theoretical structural motifs are proposed to match two experimental solid carbonic acid UV spectra from previous literature (Astron. Astrophys. 2021, 646, A172): a linear ribbon structure as a single octamer and nonplanar orientations of carbonic acid clusters. The latter have some contribution from approximated amorphous solid carbonic acid in the form of 40 different clusters of 8 carbonic acid molecules ensemble-averaged together, but unoptimized pairs of optimized dimers oriented perpendicular to one another give the strongest intensities of lower energy UV transitions. The linear ribbon structure's predicted spectrum computed with CAM-B3LYP/6-311G(d,p) agrees well with Experimental Solid Bthe β-carbonic acid experimental data in the UV region. Meanwhile, the 40 amorphous clusters are built with a randomization script, and the electronically excited states are calculated with both CAM-B3LYP/6-311G(d,p) and ωB97XD/ 6-311G(d,p). The resulting theoretical spectrum is constructed by employing a Boltzmann distribution of the intensities and artificially broadening the simulated spectra. The nonplanar dimer pairs are computed with CAM-B3LYP and B3LYP with the 6-311G(d,p) basis set. The results of the amorphous simulation weakly correspond with the Experimental Solid A spectrum, but the fully nonplanar motif matches the experiment much more convincingly. As a result, the previous work appears to have observed the traditional crystalline phase of solid carbonic acid in Experimental Solid B, whereas the nonplanar orientations of the carbonic acids in the clusters appear to correlate with Experimental Solid A. This spectral classification will aid in future laboratory work exploring the role that carbonic acid can play in low temperature, low pressure desorbed environments with potential application to astrochemistry.

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Section: ■ Introductionmentioning

confidence: 89%

Section: ■ Computational Methodsmentioning

confidence: 99%

“…The linear octamer ribbon structure is the extended structure from previous work that appears to correspond with β-carbonic acid. 20,27 This octamer is optimized with…”

Section: ■ Computational Methodsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 94%

Section: ■ Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Theoretical Characterization of Carbonic Acid Clusters in the UV

Wallace

Fortenberry

2022

J. Phys. Chem. A

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Red-Shifting the Excitation Energy of Carbonic Acid Clusters Via Nonminimum Structures

et al. 2023

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Nonminimum carbonic acid clusters provide excitation energies and oscillator strengths in line with observed ice-phase UV absorptions better than traditional optimized minima. This equation-of-motion coupled cluster quantum chemical analysis on carbonic acid monomers and dimers shows that shifts to the dihedral angle for the internal heavy atoms in the monomer produce UV electronic excitations close to 200 nm with oscillator strengths that would produce observable features. This τ(OCOO) dihedral is actually a relatively floppy motion unlike what is often expected for sp2 carbons and can be distorted by 30° away from equilibrium for an energy cost of only 11 kcal/mol. As this dihedral decreases beyond 30°, the excitation energies decrease further. The oscillator strengths do, as well, but only to a point. Hence, the lower-energy distortions of τ(OCOO) are sufficient to produce structures that exhibit excitation energies and oscillator strengths that would red-shift observed spectra of carbonic acid ices away from the highest UV absorption feature at 139 nm. Such data imply that colder temperatures (20 K) in the experimental treatment of carbonic acid ices are freezing these structures out after annealing, whereas the warmer temperature experiments (80 K) are not.

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Toward the IR Detection of Carbonic Acid: Absorption and Emission Spectra

Fortenberry,

Esposito

2024

ApJ

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With the recent radioastronomical detection of cis-trans-carbonic acid (H2CO3) in a molecular cloud toward the Galactic center, the more stable but currently unobserved cis-cis conformer is shown here to have strong IR features. While the higher-energy cis-trans-carbonic acid was detected at millimeter and centimeter wavelengths, owing to its larger dipole moment, the vibrational structure of cis-cis-carbonic acid is more amenable to its observation at micron wavelengths. Even so, both conformers have relatively large IR intensities, and some of these fall in regions not dominated by polycyclic aromatic hydrocarbons. Water features may inhibit observation near the 2.75 μm hydride stretches, but other vibrational fundamentals and even overtones in the 5.5–6.0 μm range may be discernible with JWST data. This work has employed high-level, accurately benchmarked quantum chemical anharmonic procedures to compute exceptionally accurate rotational spectroscopic data compared to experiment. Such performance implies that the IR absorption and even cascade emission spectral features computed in this work should be accurate and will provide the needed reference for observation of either carbonic acid conformer in various astronomical environments.

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Linear and Helical Carbonic Acid Clusters

Cited by 3 publications

References 35 publications

Theoretical Characterization of Carbonic Acid Clusters in the UV

Theoretical Characterization of Carbonic Acid Clusters in the UV

Red-Shifting the Excitation Energy of Carbonic Acid Clusters Via Nonminimum Structures

Toward the IR Detection of Carbonic Acid: Absorption and Emission Spectra

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