The recent synthesis of diaminomethane ((NH2)2CH2) under simulated interstellar conditions implies that this molecule is likely present in the interstellar medium (ISM), and this work provides the highly accurate quantum chemically computed rotational constants and IR frequencies for comparison to experiment that may aid in its potential future detection. This simplest geminal diamine of prebiotic note has a transition for its ν18 fundamental frequency at 702.5 cm−1 (14.23 μm) with an intensity on level with that of the antisymmetric stretch in carbon dioxide. Additionally, its 1.72 D dipole moment for the most stable C2v conformer should make it detectable with radiotelescopes as well. The C2 conformer may also be detectable in similar regions where the C2v form is present, but only warmer or higher-energy regions will allow for possible observation of the C1 conformer. In any case, rotational constants for these other two conformers are also provided in addition to the full set of fundamental vibrational frequencies for the C2v conformer. These data will assist with further laboratory classification and possible interstellar detection of this prebiotic molecule.
- Award ID(s):
- 1757220
- NSF-PAR ID:
- 10417594
- Date Published:
- Journal Name:
- Physical Chemistry Chemical Physics
- Volume:
- 24
- Issue:
- 31
- ISSN:
- 1463-9076
- Page Range / eLocation ID:
- 18552 to 18558
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract A hybrid quartic force field approach produces the same accuracies as non‐hybrid methods but for less than one quarter of the computational time. This method utilizes explicitly correlated coupled cluster theory at the singles and doubles level inclusive of perturbative triples (CCSD(T)‐F12b) in conjunction with a triple‐ basis set, core electron correlation, and scalar relativity for the harmonic terms and CCSD(T)‐F12b with a valence double‐ basis set for the cubic and quartic terms. There is no sacrifice in the prediction of fundamental anharmonic vibrational frequencies or vibrationally‐averaged rotational constants as compared to experiment, but the time saved is notable. Other hybrid methods are examined involving different sizes of basis sets and composite terms included or excluded. Not one is more accurate; only one is faster. F12 (also called F12c) is tested as well, but it has an increase in computational time for no increase in accuracy. As such, this work reports a hybrid and composite approach (F12‐TcCR+DZ) in the computation of rovibrational spectral data which can be applied to the observation of novel molecules in the gas phase in the laboratory and potentially even in astrophysical environments.
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Rovibrational spectral data for several tetra-atomic silicon carbide clusters (TASCCs) are computed in this work using a CCSD(T)-F12b/cc-pCVTZ-F12 quartic force field. Accurate theoretical spectroscopic data may facilitate the observation of TASCCs in the interstellar medium which may lead to a more complete understanding of how the smallest silicon carbide (SiC) solids are formed. Such processes are essential for understanding SiC dust grain formation. Due to SiC dust prevalence in the interstellar medium, this may also shed light on subsequent planetary formation. Rhomboidal Si2C2is shown here to have a notably intense (247 km mol−1) anharmonic vibrational frequency at 988.1 cm−1(10.1
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null (Ed.)The challenges associated with the out-of-plane bending problem in multiply-bonded hydrocarbon molecules can be mitigated in quartic force field analyses by varying the step size in the out-of-plane coordinates. Carbon is a highly prevalent element in astronomical and terrestrial environments, but this major piece of its spectra has eluded theoretical examinations for decades. Earlier explanations for this problem focused on method and basis set issues, while this work seeks to corroborate the recent diagnosis as a numerical instability problem related to the generation of the potential energy surface. Explicit anharmonic frequencies for c-(CH)C 3 H 2 + are computed using a quartic force field and the CCSD(T)-F12b method with cc-pVDZ-F12, cc-pVTZ-F12, and aug-cc-pVTZ basis sets. The first of these is shown to offer accuracy comparable to that of the latter two with a substantial reduction in computational time. Additionally, c-(CH)C 3 H 2 + is shown to have two fundamental frequencies at the onset of the interstellar unidentified infrared bands, at 5.134 and 6.088 μm or 1947.9 and 1642.6 cm −1 , respectively. This suggests that the results in the present study should assist in the attribution of parts of these aromatic bands, as well as provide data in support of the laboratory or astronomical detection of c-(CH)C 3 H 2 + .more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2CP02076A
