Theoretical study of the potential energy surfaces and dynamics of CaNC/CaCN

Nanbu, Shinkoh; Minamino, Satoshi; Aoyagi, Mutsumi

doi:10.1063/1.473815

Cited by 19 publications

(11 citation statements)

References 32 publications

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“…The derived column density of CaNC has to be considered as an upper limit because IR pumping through the low-energy ν 2 bending mode has not been considered in our calculations. Nambu et al (1997) have performed ab initio calculations for the potential energy surface of CaNC and found that the bending frequency could be particularly low (≃27 cm −1 ). Following Agúndez & Cernicharo (2006) and Agúndez et al (2017), infrared pumping can significantly increase the population of intermediate and high- N molecular levels with respect to the pure collisional excitation case.…”

Section: Discussionmentioning

confidence: 99%

Discovery of the first Ca-bearing molecule in space: CaNC

Cernicharo

Velilla-Prieto

Agúndez

et al. 2019

A&A

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We report on the detection of calcium isocyanide, CaNC, in the carbon-rich evolved star IRC+10216. We derived a column density for this species of (2±0.5)×1011 cm–2. Based on the observed line profiles and the modelling of its emission through the envelope, the molecule has to be produced in the intermediate and outer layers of the circumstellar envelope where other metal-isocyanides have previously been found in this source. The abundance ratio of CaNC relative to MgNC and FeCN is ≃1/60 and ≃1, respectively. We searched for the species CaF, CaCl, CaC, CaCCH, and CaCH3 for which accurate frequency predictions are available. Only upper limits have been obtained for these molecules.

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Section: Discussionmentioning

confidence: 99%

Discovery of the first Ca-bearing molecule in space: CaNC

Cernicharo

Velilla-Prieto

Agúndez

et al. 2019

A&A

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“…Both experimental and supporting theoretical studies have shown that the bonding in these states is strongly ionic and the unpaired electron resides primarily on the metal atom. [7][8][9][10][11][12][13] Pure rotational spectra for MgNC, [14][15][16][17] MgCN, 18 and CaNC 19,20 have also been recorded. One of the catalysts for the recent interest in the metal cyanides/isocyanides was the observation of both MgCN and MgNC free radicals in interstellar space.…”

Section: Introductionmentioning

confidence: 99%

“…16 From the l-type doubling constant, the bending frequency was found to be low, with an estimated value of 86 cm -1 . No corresponding rotationally resolved data are available for the heavier alkalineearth isocyanides; however, ab initio calculations have been performed on CaNC, and these calculations have predicted a bending frequency of 27 cm -1 in the ground electronic state, 13 suggesting a highly floppy system.…”

Section: Introductionmentioning

confidence: 99%

Laser-Induced Fluorescence Spectroscopy of the BaNC Free Radical in a Supersonic Jet

2003

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Laser-induced fluorescence spectra of the BaNC free radical in a supersonic jet have been recorded for the first time. A strong and rather complicated excitation spectrum was observed between 18 000 and 19 500 cm-1. In the corresponding dispersed fluorescence (DF) spectra, long progressions in the bending mode have been identified. The low frequency of this mode, 70 cm-1, for the fundamental demonstrates that BaNC is relatively floppy in the bending coordinate in its ground electronic state. The intensity profiles of the bending progressions suggest that BaNC undergoes a substantial change in its equilibrium bond angle on electronic excitation. This is most likely due to the formation of a bent structure in the excited electronic state. Ab initio calculations conducted in this work suggest that BaNC is linear in its ground electronic state. However, an apparent change in sign of the bending-mode anharmonicity, deduced from the DF spectra, is suggestive of a bent equilibrium structure with a small barrier to linearity.

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“…The isomerism (or polytopism) of many metal cyanides, including the lithium, 1f,2c-e,, sodium, , magnesium, 2g, potassium, 2b,e,4c,5f, and calcium 6a,i,8 monocyanides, has been investigated both experimentally and by ab initio methods. A general trend evident in these studies has been that alkali metal monocyanides preferentially adopt a π-complex structure 2,3,7 (although this does not hold true for the smallest alkali metal, lithium) while the alkaline earth monocyanides are more prone to form a linear isocyanide MNC. , In some instances, notably the cation Mg(CN) + , 6f-h all three geometries, linear MCN, linear MNC, and π-complex, are seen to be local minima according to high-level ab initio calculations, with comparatively small barriers to interconversion.…”

Section: Introductionmentioning

confidence: 99%

Magnesium Dicyanide: Three Isomers or Seven?

Petrie

1999

J. Phys. Chem. A

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We present a detailed study of the singlet potential energy surface for Mg(CN)2 using a variety of ab initio computational techniques. When second-order Møller−Plesset perturbation theory is employed in conjunction with basis sets of various sizes, seven structures for Mg(CN)2 are identified as local minima: the linear isomers NCMgCN, NCMgNC, and CNMgNC and the π-complex species NCMg-π-(CN), CNMg-π-(CN), and Mg[-π-(CN)]2 (two enantiomers). These isomers are connected by eight transition states to isomerization. However, while the linear structures are also found to be minima at all of the levels of theory employed here, the existence of the π-complexes (and, consequently, of many of the transition states) is strongly level-dependent: at B3-LYP/6-31+G*, B3-LYP/6-311+G(2df), and with Hartree−Fock calculations with a variety of basis sets, none of the π-complexes correspond to stationary points upon the potential energy surface. Furthermore, calculations employing methods designed to deliver highly accurate molecular energies (such as G2 and CBS-Q) reveal that the π-complexes located on the MP2/6-31G* surface are higher in energy than some of the putative transition states leading to linear isomers. While a more detailed examination of partially optimized structures upon the potential energy surface (using various levels of theory including QCISD/6-311G(2df), G2, and CBS-Q, with B3-LYP/6-311+G(2df) geometries) suggests that the π-complexes are, technically, local minima, we conclude that these π-complexes are, at best, highly reactive intermediates on the isomerization pathways NCMgCN ↔ NCMgNC and NCMgNC ↔ CNMgNC and that only the linear minima (NCMgCN, NCMgNC, and CNMgNC) correspond to meaningful and isolable chemical entities. According to both the G2 and CBS-Q techniques, the difference between the highest transition state and the global minimum (CNMgNC) is only ∼30 kJ mol-1.

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Theoretical study of the potential energy surfaces and dynamics of CaNC/CaCN

Cited by 19 publications

References 32 publications

Discovery of the first Ca-bearing molecule in space: CaNC

Discovery of the first Ca-bearing molecule in space: CaNC

Laser-Induced Fluorescence Spectroscopy of the BaNC Free Radical in a Supersonic Jet

Magnesium Dicyanide: Three Isomers or Seven?

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