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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2848-2861 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed re-investigation of the (0,0) and 211 bands of the A˜ 2Πu–X˜ 2Πg transition of 11BO2, near 545 nm, has been carried out from spectra taken at sub-Doppler resolution. Avoided crossings are found to occur between the 2Σ and 2Δ vibronic components of the v2=1 level of the A˜ 2Πu state. These perturbations are the first known examples of K-resonance crossings, which result from an interplay of the electronic Λ-type doubling and the vibrational l-type doubling in a state where the electrostatic parameter ε is small. It turns out that perturbations of this type must always occur in a 2Π electronic state if the ratio A/εω2 is large enough, but have not been seen until now for lack of suitable data. Their existence allows an unusually complete description of the orbital angular momentum effects in both the A˜ 2Πu and X˜ 2Πg states. It has been necessary to fit the avoided crossings by a full matrix treatment of the K resonance. In addition the A˜ 2Πu state, although it appears to be unperturbed at lower resolution, shows an astonishing number of very small random rotational perturbations. These arise from vibronic coupling between the A˜ 2Πu and X˜ 2Πg states of BO2 through the ν3 vibration, which has species σ+u; their presence is consistent with the explanation given by Kawaguchi et al. [Mol. Phys. 44, 509 (1981)] for the sizable negative anharmonicity of the ground state ν3 vibration. About 20% of the available ground state energy levels at 18 300 cm−1 appear to be active in causing level shifts and splittings in the A˜ 2Πu state. The matrix elements are quite small, ranging up to about 600 MHz, but the great number of perturbations indicates the onset of chaotic behavior.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 1003-1007 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method for calibrating high-resolution laser spectra in the visible is described. The system is based on an evacuated Fabry–Perot étalon whose cavity length is servolocked to a stabilized HeNe laser; the absolute order number of the fringe at the HeNe frequency is known and the free spectral range can be determined with high accuracy. For absolute-frequency measurements the order number of a transmission fringe is obtained from a commercial wavemeter (whose accuracy is sufficient to identify the fringe); the absolute frequency is then the HeNe frequency multiplied by the ratio of the "unknown'' order number to the "lock-point'' order number. The long-term frequency reproducibility of the system is better than 25 MHz. Small-frequency splittings such as molecular hyperfine intervals can be measured to ±1 MHz, while large-frequency intervals (of the order of 500 GHz) are consistent to better than 10 MHz.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 6-8 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method is described for stabilization of a cw CO2 laser by locking it to a modulated external cavity which is locked to a HeNe reference laser. This avoids the necessity of modulating the CO2 laser. Stability values of a few tens of kHz on the microsecond and minute time scales have been achieved.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 7300-7310 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-resolution intracavity dye laser spectroscopy has been used to obtain sub-Doppler spectra of transitions to 350 rotational levels in the 410 band of the A˜ 1A2–X˜ 1A1 electronic transition of thioformaldehyde. Ground state combination differences from the sub-Doppler spectra, combined with microwave and infrared data, have been used to improve the ground state rotational and centrifugal distortion constants of H2CS. The upper state shows a remarkable number of perturbations. The largest of these are caused by nearby triplet levels, with matrix elements of 0.05–0.15 cm−1. A particularly clear singlet–triplet avoided crossing in Ka' = 7 has been shown to be caused by interaction with the F1 component of the 3162 vibrational level of the a˜ 3A2 state. At least 53% of the S1 levels show evidence of very small perturbations by high rovibronic levels of the ground state. The number of such perturbations is small at low J, but increases rapidly beyond J=5 such that 40%–80% of the observed S1 levels of any given J are perturbed by ground state levels. Model calculations show that the density and J dependence of the number of perturbed levels can be explained if there is extensive rotation-induced mixing of the vibrational levels in the ground state.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 6240-6262 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The (0,0) band of the B 4Π–X 4Σ− transition of NbO, near 6600 A(ring), has been analyzed from spectra taken at sub-Doppler resolution. The transition is notable for the great width of its Nb nuclear hyperfine structure, which is caused principally by the unpaired 5sσ electron in the ground state interacting with the large magnetic moment of the 4193Nb nucleus (I=9/2). A fit to the ground-state combination differences, including four very precise microwave lines measured by Suenram et al. [J. Mol. Spectrosc. 148, 114 (1991)], has given a comprehensive set of rotational, spin, and hyperfine parameters. Prominent among these are the third-order spin–orbit distortions of the spin-rotation interaction and the Fermi contact interaction, which are large and well determined, reflecting different degrees of spin–orbit contamination of the the 4Σ1/2− and 4Σ3/2− components of the ground state.The δ 2π B 4Π state was hard to fit, for a number of reasons. First, its spin–orbit structure is asymmetric, because of strong perturbations by a 2Π state which has been identified in this work, from among the various weak bands in the NbO spectrum near 7000 A(ring); the result is that many high order centrifugal distortion terms are needed in an effective Hamiltonian model for the rotation. Second, the hyperfine structure is perturbed, not only by this 2Π state, but by distant Σ and Δ states at higher energy. The δ 2σ* C 4Σ− state at 21 350 cm−1 appears to be one of these. The distant states generate large apparent nuclear spin-rotation interactions, both within and between the Λ components of the Π state, as a result of cross terms between matrix elements of the operators −2BJ⋅L and aI⋅L. Similar cross terms arising from the operators AL⋅S and aI⋅L produce corrections to the Fermi contact matrix elements and are responsible for the unexpected negative sign of the magnetic hyperfine parameter d. The "off-diagonal'' quadrupole parameter e2Qq2 is very large, and causes some of the higher J line shapes of the B–X system to be noticeably asymmetric at Doppler limited resolution; its value is consistent with the electron configuration of the B 4Π state being δ 2π.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 5231-5238 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Three bands of the "red'' system of gaseous CoO have been rotationally analyzed using laser-induced fluorescence techniques. The available evidence indicates that the lower levels are the Ω=7/2 and 5/2 spin–orbit components of a 4Δi electronic state, which is assigned as the ground state of the molecule. The cobalt nuclear hyperfine splittings are small in the ground state, which suggests that no unpaired electron in a σ molecular orbital derived from the Co 4s atomic orbital is present, so that the electron configuration is presumably σ2δ3π2; the ground state bond length (r0) is 1.631 A(ring). The upper electronic levels are heavily perturbed, both rotationally and vibrationally, and their hyperfine structures, though following case (a) behavior, are large and irregular. This work on CoO completes the determination of the ground state symmetries and bond lengths for the whole series of the 3d transition metal monoxides; some comparisons for the members of the series are given.
    Type of Medium: Electronic Resource
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