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  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The A˜ 2Σ+–X˜ 2Πi transition of jet-cooled silicon methylidyne, SiCH, has been recorded by laser-induced fluorescence in the 850–600 nm region. The radical was produced in an electric discharge using tetramethylsilane as the precursor. Fifteen cold bands of SiCH and 16 bands of SiCD have been assigned vibrationally, giving the upper state frequencies as v2′=715/558 cm−1 and v3′=1168/1127 cm−1 for SiCH/SiCD. Rotational analysis of the 000 and 303 bands for each isotopomer has given the following molecular structures: r0″(Si–C)=1.692 52(8), r0″(C–H)=1.0677(4), r0′(Si–C)=1.6118(1), and r0′(C–H)=1.0625(5) Å. The silicon–carbon bond length in the X˜ 2Π ground state of SiCH (electron configuration ...σ2π3) is typical for a Si=C double bond; in the A˜ 2Σ+ excited state (...σ1π4) it corresponds to a triple bond. This work provides the first experimental measurement of the length of the carbon–silicon triple bond. © 2000 American Institute of Physics.
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  • 2
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic spectrum of germylidene (H2C(Double Bond)Ge), the simplest unsaturated germylene, has been observed for the first time. Jet-cooled H2CGe and D2CGe were produced by an electric discharge through tetramethylgermane diluted in argon at the exit of a supersonic expansion. High-resolution spectra of H2C74Ge and D2C74Ge, obtained from (CH3)4〈sup ARRANGE="STAGGER"〉74Ge prepared from isotopically enriched 74Ge metal, have been rotationally analyzed to yield the following r0 structures: r0″(CGe)=1.7908(2) Å, r0″(CH)=1.1022(5) Å, θ0″(HCH)=115.05(5)°, r0′(CGe)=1.914(4) Å, r0′(CH)=1.082(9) Å, and θ0′(HCH)=139.3(11)°. The 367–354 nm B˜1B2–X˜ 1A1 band system consists of prominent perpendicular bands involving the CGe stretching (ν3) and CH2 scissors (ν2) vibrations and a weaker series of vibronically induced parallel bands involving the CH2 rocking mode (ν6). Vibronic bands involving Δv=2 changes in ν6(b2) and ν4(b1) have also been assigned. The fluorescence decays of single rotational levels of the 000 band of H2C74Ge exhibit molecular quantum beats for about 70% of the levels surveyed. Density of states arguments reveal that most of the beats originate from interactions with high rovibronic levels of the ground state. In one case, hyperfine splittings in the Fourier transform of the beat pattern indicate an accidental coincidence with an excited triplet state level. The less frequent occurrence of quantum beats in germylidene compared to silylidene, where they are almost universal, can be attributed to the smaller density of ground state levels at the zero-point energy of the S2 state in the former. © 1999 American Institute of Physics.
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  • 3
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A skimmed molecular beam of silicon methylidyne, SiCH, was produced using a pulsed discharge jet source with methyltrichlorosilane as the precursor. Linewidths of 35 MHz were achieved using laser-induced fluorescence detection. The field-free fine and magnetic hyperfine interactions and Stark effects were analyzed for the A˜ 2Σ+-X˜ 2Π3/2 component of the 301 band at 12 934.428 cm−1. The observed proton hyperfine structure was satisfactorily reproduced with a single upper state Fermi contact parameter bF=117(2) MHz. The determined permanent electric dipole moments are μ(A˜ 2Σ+)=1.51(2) D and μ(X˜ 2Π3/2)=0.066(2) D. Our ab initio predictions of the Fermi contact parameter and dipole moments at the B3LYP and quadratic configuration interaction including single and double substitutions levels of theory are in reasonable accord with experiment. An interpretation of the magnitudes of the determined parameters is given based on the highest occupied molecular orbitals. The very small ground state dipole moment will make microwave and radioastronomy studies of SiCH very challenging. © 2001 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 5047-5052 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The germanium methylidyne (GeCH) radical has been studied at high resolution by laser-induced fluorescence spectroscopy in a skimmed molecular beam. The radical was produced in a pulsed discharge jet source using methyltrichlorogermane as the precursor. Single rotational lines of the A˜ 2Σ+–X˜ 2Π3/2 component of the 000 band at 14 070 cm−1 were recorded with linewidths of 35 MHz, showing resolved proton magnetic hyperfine splittings. The observed hyperfine splittings of 12 rotational lines were satisfactorily modeled by varying a single upper state Fermi contact parameter, giving bF=163(2) MHz. Optical Stark measurements were performed on the 74GeCH P11(3/2)F′=1 hyperfine transition and the permanent electric dipole moments determined to be μ(X˜ 2Π)=0.122(2) D and μ(A˜ 2Σ+)=1.29(2) D. Our ab initio predictions of the dipole moments and excited state Fermi contact parameter are in fair agreement with experiment. The magnitudes of the determined parameters are discussed based on the molecular orbitals and compared to similar measurements on SiCH. © 2001 American Institute of Physics.
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  • 5
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground state vibrational energy levels of jet-cooled H2CSi and D2CSi have been studied by a combination of wavelength-resolved fluorescence and stimulated emission pumping (SEP) techniques. By taking advantage of the vibrational selection rules and Franck–Condon factors and selectively pumping upper state single vibronic levels, readily assignable low-resolution emission spectra were obtained. Higher resolution SEP spectra were recorded to give precise measurements of the vibrational band origins of many of the lower-lying vibrational levels. All of the vibrational frequencies, except for the Franck–Condon inactive CH asymmetric stretching mode, ν5, have been determined for both isotopomers. The CH2 rocking mode (ν6) is found to have a very low 263 cm−1 frequency in the ground state. The spectra are complicated by unexpected activity in the out-of-plane bending vibration. © 2001 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 7827-7834 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The A˜ 1A″–X˜ 1A′ spectra of jet-cooled HSiI and DSiI have been studied using the pulsed discharge technique, using H3SiI and D3SiI as precursors. The excited state vibrational frequencies have been determined and the literature value of ν1′ substantially revised. Although a reliable excited state equilibrium structure was unattainable, the rotational constants of the 000 bands gave the structural parameters r0″(Si–I)=2.463(1) Å, r0″(Si–H)=1.534(1) Å, θ0″(HSiI)=92.4(1)°, r0′(Si–I)=2.436(1) Å, r0′(Si–H)=1.515(5) Å, and θ0′(HSiI)=114.9(2)°. The radiative lifetime of the 000 band has been measured to be 1230±30 ns. Trends in the structural parameters, vibrational frequencies, and their changes on electronic excitation for the monohalosilylenes have been discussed. © 1998 American Institute of Physics.
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  • 7
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground state vibrational energy levels of jet-cooled SiCH and SiCD have been studied by a combination of laser-induced fluorescence and wavelength-resolved fluorescence techniques. The radicals were produced by a pulsed electric discharge at the exit of a supersonic expansion using tetramethylsilane or methyltrichlorosilane as the precursor. Emission spectra have been obtained by pumping both perpendicular and parallel (vibronically induced) bands, providing complementary information on the Si–C stretching and Si–C–H bending modes. Ground state energy levels up to 4000 cm−1 have been assigned and fitted using a vibrational Hamiltonian that incorporates Renner–Teller, spin–orbit, vibrational anharmonicity, and Fermi resonance interactions. The validity of the derived parameters has been tested using the isotope relations. © 2001 American Institute of Physics.
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  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The A˜ 1B1–X˜ 1A1 electronic transition of germylene has been reinvestigated. A room temperature absorption spectrum of the central portion of the 000 band of GeH2 has been obtained using the technique of laser optogalvanic spectroscopy. A rotationally resolved spectrum of the 000 band of jet-cooled GeD2 has been recorded with a pulsed discharge source. Analysis of these spectra has yielded ground and excited state rotational constants for the 74GeH2, 72GeH2, 70GeH2, 76GeD2, 74GeD2, 72GeD2, and 70GeD2 isotopomers and approximate equilibrium structures of: r″(Ge–H)=1.5883(9) Å, θ″(H–Ge–H)=91.22(4)°, r′(Ge–H)=1.5471(6) Å, and θ′(H–Ge–H)=123.44(2)°. The ground state ν1 and ν2 vibrational frequencies have been determined from wavelength-resolved fluorescence spectra of jet-cooled GeH2 and GeD2. There is good evidence that GeH2 rotational levels with Ka′〉1 are so strongly predissociated that lifetime broadening makes them diffuse, severely restricting the information that can be obtained from absorption and laser-induced fluorescence experiments. © 2000 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8417-8425 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The A˜ 2Σ+–X˜ 2Πi electronic transition of jet-cooled germanium methylidyne has been recorded in the 730–555 nm region by laser-induced fluorescence techniques. The radical was produced in a pulsed electric discharge using tetramethylgermane as the precursor. The band system consists of perpendicular and vibronically induced parallel bands with upper state frequencies of ν2′=638/497 cm−1 and ν3′=990/952 cm−1 for GeCH/GeCD. The 2Σ+–2Π3/2 components of the 000 bands of GeCH and GeCD and the 201 band of GeCH have been recorded with sufficient resolution to assign the transitions of the 70Ge, 72Ge, 74Ge, and 76Ge isotopomers. The rotational constants of the various hydrogen and germanium isotopomers were used to derive the following molecular structures: r0″(Ge–C)=1.775 79(21) Å, r0″(C–H)=1.0673(12) Å, r0′(Ge–C)=1.673 66(8) Å, and r0′(C–H)=1.0589(5) Å. The ground state germanium–carbon bond length is typical for a Ge=C double bond, but in the excited state it corresponds to a triple bond. This is a consequence of promotion of an electron from a nonbonding σ orbital to a π bonding orbital to form the ...σ1π4(2Σ+) excited state. In this study we provide the first experimental value for the length of the germanium–carbon triple bond. © 2000 American Institute of Physics.
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