Discovery of a Missing Link: Detection and Structure of the Elusive Disilicon Carbide Cluster

McCarthy, Michael; Baraban, Joshua H.; Changala, P. Bryan; Stanton, John F.; Martin‐Drumel, Marie‐Aline; Thorwirth, Sven; Gottlieb, C. A.; Reilly, Neil J.

doi:10.1021/acs.jpclett.5b00770

Cited by 40 publications

(48 citation statements)

References 30 publications

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“…Guided by high-level theoretical calculations, it was ultimately possible to detect the rotational spectrum of the carbon-13 substituted species Si 13 CSi in the centimeter-band, followed by the normal species SiCSi in the same frequency range 60. Si 13 CSi was targeted first because replacing 12 C with the heavier 13 C has the beneficial effect of shifting the entire spectrum to lower frequency by roughly 10% (owing to the smaller A value), which is significant because the strong 1 1,1 → 2 0,2 transition now falls close to 38 GHz, a frequency well within the operating range of our FT microwave spectrometer, rather than near 43 GHz for the normal species, which is very close to the upper frequency ceiling, and consequently where search capabilities are considerably more challenging.…”

Section: Disilicon Carbide Sicsi a Possible Progenitor For Dustmentioning

confidence: 99%

“…Table 3 summarizes the laboratory data set for the normal isotopic species, which extends from 6 to 186 GHz, 1 ≤ J ′ ≤ 20, and 0 ≤ K a ≤ 2. Subsequent isotopic measurements in the same frequency range and covering similar degree of rotational excitation enabled a determination of a precise semi-experimental (reSE) molecular structure that accounts for the effects of zero-point vibrational motion, yielding a Si-C bond length of 1.693(1) Å, and apex angle of 114.87(5)°, where the numbers in parenthesis denote 1 σ errors 60…”

Section: Disilicon Carbide Sicsi a Possible Progenitor For Dustmentioning

confidence: 99%

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Building Blocks of Dust and Large Organic Molecules: A Coordinated Laboratory and Astronomical Study of Agb Stars

McCarthy¹,

Gottlieb²,

Cernicharo³

2017

Proceedings of the 72nd International Symposium on Molecular Spectroscopy

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This article provides an overview of recent astronomical studies and a closely coordinated laboratory program devoted to the study of the physics and chemistry of carbon rich Asymptotic Giant Branch (AGB) stars. The increased sensitivity and angular resolution of high altitude ground-based millimeter-wave interferometers in the past few years has enabled molecular astronomers to determine the excitation and spatial distribution of molecules within a few stellar radii of the central star where the molecular seeds of dust are formed, and to critically assess the physicochemical mechanisms of dust formation and growth. However the astronomical studies are crucially dependent on precise laboratory measurements of the rotational spectra — both in the ground and vibrationally excited states of the normal and rare isotopic species — of the principal molecules in the inner region which appear to contain only two or three heavy atoms Much remains to be done by laboratory spectroscopists as evidenced by the large number of unassigned millimeters-wave rotational lines that are observed in the inner envelope of carbon rich AGB stars. As an illustration we refer to the example of an initial laboratory approach for establishing whether vibrationally excited SiC2 and HCN are the carriers of some of the unassigned features observed in the prototypical carbon rich AGB star IRC+10216 with ALMA. Also highlighted are ongoing laboratory studies of the silicon carbides SiC2 and SiCSi in their ground and excited vibrational states, and SiC3 in the ground vibrational state. Following the initial detection of SiC3 and SiCSi in the outer molecular envelope of IRC+10216, the laboratory spectroscopy was extended to higher frequency in support of the recent interferometric measurements. Thirty-two new millimeter-wave rotational transitions of SiCSi with J ≤ 48, Ka ≤ 3 and upper level energies Eu ≤ 484 K in the range from 178 – 391 GHz, and 35 new transitions of SiC3 with J ≤ 38, Ka ≤ 20 and Eu ≤ 875 K between 315 and 440 GHz were measured in the laboratory. In addition five to six rotational transitions in one quanta of each of the three fundamental vibrational modes of SiCSi, and the two lowest rotational transitions in the previously unexplored C–C stretching mode (ν1) of SiCC were measured in the normal and doubly substituted 13C isotopic species.

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Section: Disilicon Carbide Sicsi a Possible Progenitor For Dustmentioning

confidence: 99%

Section: Disilicon Carbide Sicsi a Possible Progenitor For Dustmentioning

confidence: 99%

Building Blocks of Dust and Large Organic Molecules: A Coordinated Laboratory and Astronomical Study of Agb Stars

McCarthy¹,

Gottlieb²,

Cernicharo³

2017

Proceedings of the 72nd International Symposium on Molecular Spectroscopy

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“…An example of this is the recent discovery of SiCSi, the first disilicon compound observed in space. SiCSi bands were reported in 2015 observed toward IRC +10216 by a multinational team led, in part, by Thaddeus's successor at the Harvard–Smithsonian Center for Astrophysics, Michael C. McCarthy . This team was comprised of numerous laboratory experimentalists, observationalists, and quantum chemists whose synergy was absolutely essential to characterize the necessary spectroscopic constants for comparison to the stellar features.…”

Section: Quantum Chemistry In Astrochemical Detectionmentioning

confidence: 99%

Quantum astrochemical spectroscopy

Fortenberry

2016

Int J of Quantum Chemistry

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In this review, the origins of astrochemistry and the initial applications of quantum chemistry to the discovery of new molecules in space are discussed. Furthermore, more recent successes and failures of quantum astrochemistry are explored. Finally, the application of quantum chemistry to the chemical study of space is driving developments in large-scale computational science. Consequently, cloud computing and large molecule computations are discussed. Astrochemistry is a natural application of quantum chemistry. The ability to analyze routinely and completely the structural, spectroscopic, and electronic properties of any given molecule, regardless of its laboratory stability, make this tool a necessary component for astrochemical analysis. The sizes of the computations scaling with the number of electrons and degrees-of-freedom can become limiting, but proper choices of methods can provide unique insights. The chemistry of the Earth is a small snapshot of the chemistries available in the universe at large, and the flexibility inherent within computation make quantum chemistry an excellent driver of new knowledge in fundamental molecular science as well as in astrophysics.

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“…The size of the 1D DVR basis sets in the VSCF portion of the calculation as well as the size of the virtual configuration space in the VMP2 sums were both enlarged until the vibrational energies converged to the reported precision. The VMP2, VPT2, and variational calculations were all performed with a potential surface calculated at the frozen core (FC)-CCSD(T)/cc-pVQZ level of theory, with the variational results taken from our previous work [29,30]. Table I compares the quartic rotational Hamiltonian predictions for the vibrational ground state as well as the excited fundamental levels.…”

Section: A Disilicon Carbide Si2cmentioning

confidence: 99%

“…After discussing the theoretical details, we present specific applications to two representative non-rigid molecules. The first is disilicon carbide, Si 2 C. While this molecule does have a well defined Si-C-Si bent equilibrium geometry [29], the barrier to linearity is relatively small (∼800 cm −1 ) [30]. The low energy bending mode, which has a fundamental frequency of only 142 cm −1 [30], is highly anharmonic and causes problems for VPT2 in combination with a standard rectilinear quartic force field (QFF).…”

Section: Introductionmentioning

confidence: 99%

Ab initio effective rotational and rovibrational Hamiltonians for non-rigid systems via curvilinear second order vibrational Møller–Plesset perturbation theory

Changala

Baraban

2016

The Journal of Chemical Physics

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We present a perturbative method for ab initio calculations of rotational and rovibrational effective Hamiltonians of both rigid and non-rigid molecules. Our approach is based on a curvilinear implementation of second order vibrational Møller-Plesset perturbation theory extended to include rotational effects via a second order contact transformation. Though more expensive, this approach is significantly more accurate than standard second order vibrational perturbation theory for systems that are poorly described to zeroth order by rectilinear normal mode harmonic oscillators. We apply this method to and demonstrate its accuracy on two molecules: SiC, a quasilinear triatomic with significant bending anharmonicity, and CHNO, which contains a completely unhindered methyl rotor. In addition to these two examples, we discuss several key technical aspects of the method, including an efficient implementation of Eckart and quasi-Eckart frame embedding that does not rely on numerical finite differences.

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Discovery of a Missing Link: Detection and Structure of the Elusive Disilicon Carbide Cluster

Cited by 40 publications

References 30 publications

Building Blocks of Dust and Large Organic Molecules: A Coordinated Laboratory and Astronomical Study of Agb Stars

Building Blocks of Dust and Large Organic Molecules: A Coordinated Laboratory and Astronomical Study of Agb Stars

Quantum astrochemical spectroscopy

Ab initio effective rotational and rovibrational Hamiltonians for non-rigid systems via curvilinear second order vibrational Møller–Plesset perturbation theory

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