TOWARD DETECTION OF AlCH<sub>2</sub>AND AlCH$_{{2}}^+$ IN THE INTERSTELLAR MEDIUM

Compaan, K.; Agarwal, Jay; Dye, Bryson; Yamaguchi, Yukio; Schaefer, Henry F.

doi:10.1088/0004-637x/778/2/125

Cited by 5 publications

(6 citation statements)

References 31 publications

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“…While ROHF recovers a planar structure with C2v symmetry, UHF converges to a Cs pyramidal structure with the Al-C bond ~9° out of the HCH plane. These instabilities also account for the anomalously large core correlation effects reported by Schaefer and co-workers, 2 which should instead be considered as a side effect of the UHF spatial instability. Indeed, frequencies calculated with single reference methods based on ROHF orbitals correlating all electrons (AE) or with frozen core (FC) (compare entries e, f and g, h in Table I) are rather immune from core correlation effects, with differences less than 20 cm -1 .…”

Section: A General Resultsmentioning

confidence: 83%

“…(core)(5a1) 2 (2b2) 2 (6a1) 2 (7a1) 1 (2b1) 2 and the unpaired electron is located mainly on the aluminum atom. This leads to a substantial shortening (~ −0.15 Å) of the Al-C bond, and the excited state structure can be represented as •Al=CH2.…”

Section: The Low-lying a ~ 2 A 1 Electronic Excited Statementioning

confidence: 99%

“…It has also been suggested on the basis of the abundance of aluminum and methylene in space that this species is a potential interstellar molecule. 2 The radical has yet to be identified spectroscopically, either in the gas phase or in matrices. The low molecular weight (41 g/mol), large rotational constants (A ~ 10 cm -1 ), small number of electrons (21), and lack of isotopic complications ( 27 Al = 100%) make it a very attractive species for both spectroscopic and quantum chemical studies.…”

Section: Introductionmentioning

confidence: 99%

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Ab initio spectroscopy of the aluminum methylene (AlCH2) free radical

Tarroni

Clouthier

2020

The Journal of Chemical Physics

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Extensive ab initio investigations of the ground and electronic excited states of the AlCH2 free radical have been carried out in order to predict the spectroscopic properties of this, as yet, undetected species. Difficulties with erratic predictions of the ground state vibrational frequencies, both in the literature and in the present work, have been traced to serious broken-symmetry instabilities in the unrestricted Hartree-Fock orbitals at the ground state equilibrium geometry. The use of restricted open-shell Hartree–Fock or complete active space self consistent field orbitals avoids these problems and leads to consistent and realistic sets of vibrational frequencies for the ground state. Using the internally contracted multireference configuration interaction method with aug-cc-pV(T+d)Z basis sets, we have calculated the geometries, energies, dipole moments, and vibrational frequencies of eight electronic states of AlCH2 and AlCD2. In addition, we have generated Franck–Condon simulations of the expected vibronic structure of the Ã−X̃, B̃−X̃, C̃−X̃, and C̃−Ã band systems, which will be useful in searches for the electronic spectra of the radical. We have also simulated the expected rotational structure of the 0–0 absorption bands of these transitions at modest resolution under supersonic expansion cooled conditions. Our conclusion is that if AlCH2 can be generated in sufficient concentrations in the gas phase, it is most likely detectable through the B̃2A2–X̃2B1 or C̃2A1–X̃2B1 electronic transitions at 515 nm and 372 nm, respectively. Both band systems have vibrational and rotational signatures, even at modest resolution, that are diagnostic of the aluminum methylene free radical.

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Section: A General Resultsmentioning

confidence: 83%

Section: The Low-lying a ~ 2 A 1 Electronic Excited Statementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ab initio spectroscopy of the aluminum methylene (AlCH2) free radical

Tarroni

Clouthier

2020

The Journal of Chemical Physics

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“…Electronic structure theory is well-suited for examining circumstellar systems, especially given the difficulty inherent in reproducing astral environments in the laboratory. − Moreover, the large number of species present in circumstellar media often yields overlapping spectral features, which may be disentangled using accurate vibrational predictions . In the current research, the structure, bonding, and relative thermodynamic stability of select group 15 (OPP, OPAs, and OPSb) and group 16 (SPN, SePN, and TePN) congeners of OPN are examined.…”

Section: Introductionmentioning

confidence: 99%

“…32−36 Moreover, the large number of species present in circumstellar media often yields overlapping spectral features, which may be disentangled using accurate vibrational predictions. 37 In the current research, the structure, bonding, and relative thermodynamic stability of select group 15 (OPP, OPAs, and OPSb) and group 16 (SPN, SePN, and TePN) congeners of OPN are examined. Relative energies of these molecules are reported at the complete basis set limit of CCSDT(Q) from focal point analyses.…”

Section: ■ Introductionmentioning

confidence: 99%

Structures, Bonding, and Energetics of Potential Triatomic Circumstellar Molecules Containing Group 15 and 16 Elements

2015

Self Cite

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The recent discovery of PN in the oxygen-rich shell of the supergiant star VY Canis Majoris points to the formation of several triatomic molecules involving oxygen, nitrogen, and phosphorus; these are also intriguing targets for main-group synthetic inorganic chemistry. In this research, high-level ab initio electronic structure computations were conducted on the potential circumstellar molecule OPN and several of its heavier group 15 and 16 congeners (SPN, SePN, TePN, OPP, OPAs, and OPSb). For each congener, four isomers were examined. Optimized geometries were obtained with coupled cluster theory [CCSD(T)] using large Dunning basis sets [aug-cc-pVQZ, aug-cc-pV(Q+d)Z, and aug-cc-pVQZ-PP], and relative energies were determined at the complete basis set limit of CCSDT(Q) from focal point analyses. The linear phosphorus-centered molecules were consistently the lowest in energy of the group 15 congeners by at least 6 kcal mol(-1), resulting from double-triple and single-double bond resonances within the molecule. The linear nitrogen-centered molecules were consistently the lowest in energy of the group 16 congeners by at least 5 kcal mol(-1), due to the electronegative central nitrogen atom encouraging electron delocalization throughout the molecule. For OPN, OPP, and SPN, anharmonic vibrational frequencies and vibrationally corrected rotational constants are predicted; good agreement with available experimental data is observed.

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Structure, Bonding, and Reactivity of Organoaluminum Molecular Species: A Computational Perspective

Eisenstein

Gérard

2017

Patai's Chemistry of Functional Groups

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This chapter describes the theoretical studies of organoluminum molecules involving one or more aluminum centers, as well aluminum hydride and halide. Selected systems containing other Group 13 elements are also included when they contribute to the understanding of organoaluminum systems. This review includes small to large molecular systems and mono to polyaluminum species that have been studied by a wide variety of methods from molecular orbital analysis and semiempirical methods to the most elaborate wave‐function correlated methods. The electronic structures are presented, and the structure–electronic structure relationships are discussed. The calculations illustrate how the oxidation states and the coordination number influence the structural and electronic properties of the complexes. The Lewis acid character of Al III , the polarity of the Al(δ+)–C(δ−) bond, and the rarity of the multiple bond to Al appear as the leading factors. Carbon monoxide, alkyl, alkene, alkyne, aryl, cyclopentadienyl, and arene complexes of aluminum are described in detail. The polyaluminum species include systems with direct Al–Al interaction or interaction by way of bridging groups. The structures and role of methyl aluminum oxides (MAO) on polymerization are presented. The chapter ends with the description of mechanisms for reactions of selected organoaluminum reagents derived from computational studies.

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TOWARD DETECTION OF AlCH₂AND AlCH$_{{2}}^+$ IN THE INTERSTELLAR MEDIUM

Cited by 5 publications

References 31 publications

Ab initio spectroscopy of the aluminum methylene (AlCH2) free radical

Ab initio spectroscopy of the aluminum methylene (AlCH2) free radical

Structures, Bonding, and Energetics of Potential Triatomic Circumstellar Molecules Containing Group 15 and 16 Elements

Structure, Bonding, and Reactivity of Organoaluminum Molecular Species: A Computational Perspective

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TOWARD DETECTION OF AlCH2AND AlCH$_{{2}}^+$ IN THE INTERSTELLAR MEDIUM

Cited by 5 publications

References 31 publications

Ab initio spectroscopy of the aluminum methylene (AlCH2) free radical

Ab initio spectroscopy of the aluminum methylene (AlCH2) free radical

Structures, Bonding, and Energetics of Potential Triatomic Circumstellar Molecules Containing Group 15 and 16 Elements

Structure, Bonding, and Reactivity of Organoaluminum Molecular Species: A Computational Perspective

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TOWARD DETECTION OF AlCH₂AND AlCH$_{{2}}^+$ IN THE INTERSTELLAR MEDIUM