Silicon molecules in space and in the laboratory

McCarthy, Michael; Gottlieb, C. A.; Thaddeus, P.

doi:10.1080/0026897021000035197

Cited by 101 publications

(85 citation statements)

References 52 publications

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“…Those from the J ϭ 3͞2 level of ground state SiH (X 2 ͟ 1/2 ), for example, lie near 5.7 GHz (24). This radical might be best produced from silane, a source that has already been used to study a number of silicon molecules in this laboratory (25); l-doublets from the somewhat heavier radical, C 2 H, have recently been detected here from the 2 mode lying 370 cm Ϫ1 above ground (S. Brünken, personal communication).…”

Section: Discussionmentioning

confidence: 99%

Detection of low-frequency lambda-doublet transitions of the free ¹² CH and ¹³ CH radicals

McCarthy

Mohamed

Brown

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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By Fourier transform microwave spectroscopy, lambda-doubling transitions of 12 CH and 13 CH in the lowest rotational levels of the X 2 ͟1/2 ground state have been directly detected, which has not been done previously. For both radicals, hyperfine-split lines have been measured to an accuracy of better than 1 ppm between 3 and 15 GHz, an improvement of at least 2 orders of magnitude over previous laboratory data. The measured frequencies have been combined with all previous data for CH and 13 CH in the v ‫؍‬ 0 level of the X 2 ͟ electronic state to determine improved hyperfine parameters. The production of CH from various gases also has been studied and, with methanol, the yield of CH relative to OH. Astronomical studies of CH in higher rotational levels and 13 CH can now be undertaken on the basis of the present work.microwave spectroscopy ͉ molecular data ͉ radio astronomy T he CH radical is widely distributed in astronomical sources, observed in planetary atmospheres, comets, HI and HII regions, dark molecular clouds, and planetary nebulae. It was one of the first interstellar molecules identified (1, 2), by means of detection in the optical band of a single line [R 2 (1)] near 4,300 Å of the A 2 ⌬ 3 X 2 ͟ electronic transition. It has now been observed in other parts of the spectrum as follows: (i) in the radio, by detection of lambda-doubling transitions near 3.3 GHz (3-5) in the lowest rotational level (J ϭ 1͞2) of the X 2 ͟ 1/2 state; (ii) near 700 MHz (6) in the lowest rotational level of the upper fine structure ladder (X 2 ͟ 3/2 ); (iii) in the far-infrared (FIR), by detection in both absorption (7) and emission (8) of its fundamental rotational transitions at 149.09 and 149.39 m; and (iv) in the far UV, including the diffuse feature at 1369.13 Å (9). There is little astronomical data on the rare isotopic species 13 CH, but some of its lines have been identified in the solar spectrum (10).Because of the astronomical importance of CH, considerable effort has been devoted in the laboratory to measure its rotational spectrum. Early studies by laser magnetic resonance (ref.11 and references therein) allowed some of the more interesting lines to be predicted to an uncertainty of Ϸ2 MHz. Since then, more accurate FIR spectra (good to 100 kHz; ref. 12) and submillimeter-wave spectra (good to 30-100 kHz; ref. 13) have been obtained, as well as microwave-optical double resonance (MODR) measurements (14, 15) and a few centimeter-wave measurements at fairly high J ϳ 6.5 (16) to better pin down the lambda-doubling intervals. 13 CH has been studied by some of the same techniques (17-19), but owing to the lack of tunable FIR measurements, its rotational spectrum until now could only be predicted to a few megahertz.Although much laboratory spectroscopy has already been done on CH and 13 CH, still more is needed: many of the lambda-doubling transitions have not been measured to high precision, and only a small number of the FIR spin-rotational intervals have been detected at adequately high signal-to-noise. It is parti...

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Section: Discussionmentioning

confidence: 99%

Detection of low-frequency lambda-doublet transitions of the free ¹² CH and ¹³ CH radicals

McCarthy

Mohamed

Brown

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

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“…3,8 In addition, hydrogen passivation of the highly reactive bare silicon clusters and cages has been suggested as a possible route to generate novel stable silicon nanostructures with potential applications in materials science. 9,10 To this end, we set up a program to systematically characterize the geometric and electronic structure of Si Neutral Si 2 H 6 is a well-characterized molecule.…”

Section: Introductionmentioning

confidence: 99%

“…40,41 The 12 vibrational fundamentals of Si 2 H 6 , n [1][2][3][4][5][6][7][8][9][10][11][12] , transform in D 3d as G vib = 3a 1g + a 1u + 2a 2u + 3e u + 3e g . We follow the notation of vibrational modes given previously in ref.…”

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confidence: 99%

Infrared spectrum of the disilane cation (Si2H6+) from Ar-tagging spectroscopy

Savoca

George

Langer

et al. 2013

Phys. Chem. Chem. Phys.

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“…Recently, these experimental techniques include photoelectron spectroscopy 7,8 and Fourier transform microwave spectroscopy. [9][10][11][12] SiC 3 is of particular interest as there is experimental evidence for the presence of three isomers, two singlet cyclic rings with either two ͑2s͒ or three ͑3s͒ Si-C bonds, 9,11 and a linear triplet ͑1t͒. 8 These structures are illustrated in Fig.…”

Section: Introductionmentioning

confidence: 99%

A systematic multireference perturbation-theory study of the low-lying states of SiC3

Rintelman

Gordon

Fletcher

et al. 2006

The Journal of Chemical Physics

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The three known lowest-energy isomers of SiC3, two cyclic singlets (2s and 3s) and a linear triplet (1t), have been reinvestigated using multireference second-order perturbation theory (MRPT2). The dependence of the relative energies of the isomers upon the quality of the basis sets and the sizes of the reference active spaces is explored. When using a complete-active-space self-consistent-field reference wave function with 12 electrons in 11 orbitals [CASSCF (12,11)] together with basis sets that increase in size up to the correlation-consistent polarized core-valence quadruple zeta basis set (cc-pCVQZ), the MRPT2 method consistently predicts the linear triplet to be the most stable isomer. A new parallel direct determinant MRPT2 code has been used to systematically explore reference spaces that vary in size from CASSCF (8,8) to full optimized reaction space [FORS or CASSCF (16,16)] with the cc-pCVQZ basis. It is found that the relative energies of the isomers change substantially as the active space is increased. At the best level of theory, MRPT2 with a full valence FORS reference, the 2s isomer is predicted to be more stable than 3s and 1t by 4.7 and 2.2kcal∕mol, respectively. Theoretical investigation of the eight low-lying electronic states of the cis-and trans-nitric oxide dimers and its isomerization using multiconfigurational second-order perturbation theory (CASPT2) J. Chem. Phys. 112, 6608 (2000) The three known lowest-energy isomers of SiC 3 , two cyclic singlets ͑2s and 3s͒ and a linear triplet ͑1t͒, have been reinvestigated using multireference second-order perturbation theory ͑MRPT2͒. The dependence of the relative energies of the isomers upon the quality of the basis sets and the sizes of the reference active spaces is explored. When using a complete-active-space self-consistent-field reference wave function with 12 electrons in 11 orbitals ͓CASSCF ͑12, 11͔͒ together with basis sets that increase in size up to the correlation-consistent polarized core-valence quadruple zeta basis set ͑cc-pCVQZ͒, the MRPT2 method consistently predicts the linear triplet to be the most stable isomer. A new parallel direct determinant MRPT2 code has been used to systematically explore reference spaces that vary in size from CASSCF ͑8,8͒ to full optimized reaction space ͓FORS or CASSCF ͑16,16͔͒ with the cc-pCVQZ basis. It is found that the relative energies of the isomers change substantially as the active space is increased. At the best level of theory, MRPT2 with a full valence FORS reference, the 2s isomer is predicted to be more stable than 3s and 1t by 4.7 and 2.2 kcal/ mol, respectively.

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Silicon molecules in space and in the laboratory

Cited by 101 publications

References 52 publications

Detection of low-frequency lambda-doublet transitions of the free ¹² CH and ¹³ CH radicals

Detection of low-frequency lambda-doublet transitions of the free ¹² CH and ¹³ CH radicals

Infrared spectrum of the disilane cation (Si2H6+) from Ar-tagging spectroscopy

A systematic multireference perturbation-theory study of the low-lying states of SiC3

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Silicon molecules in space and in the laboratory

Cited by 101 publications

References 52 publications

Detection of low-frequency lambda-doublet transitions of the free 12 CH and 13 CH radicals

Detection of low-frequency lambda-doublet transitions of the free 12 CH and 13 CH radicals

Infrared spectrum of the disilane cation (Si2H6+) from Ar-tagging spectroscopy

A systematic multireference perturbation-theory study of the low-lying states of SiC3

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Detection of low-frequency lambda-doublet transitions of the free ¹² CH and ¹³ CH radicals

Detection of low-frequency lambda-doublet transitions of the free ¹² CH and ¹³ CH radicals