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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 87 (1983), S. 2636-2636 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 1630-1637 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Intracavity dye laser spectroscopy has been used to obtain sub-Doppler spectra of selected rotational lines in the A˜ 1A2–X˜ 1A1 410 band of thioformaldehyde with very high resolution and sensitivity. Many of the spectra show extra lines due to perturbations involving high vibrational levels of the ground state. Most of the perturbations observed for K'a = 0 and 4 are found to correlate well with previous observations of anomalously long single rotational level fluorescence lifetimes and reduced quantum yields [J. Dunlop and D. J. Clouthier, J. Chem. Phys. 93, 6371 (1990)]. S1–S0 interaction matrix elements of 0.001–0.006 cm−1 are found for levels involved in simple two level perturbations. The large number of small random perturbations by levels of the ground state is indicative of the first stages of the onset of quantum chaos in a small molecule. Some larger perturbations in the rotational structure are also observed; these are caused by additional local interactions with levels of the nearby triplet state.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed analysis of the rotational and hyperfine structure of the (0,0) band of the B 3Φ–X 3Δ electronic transition of NbN has been performed from sub-Doppler spectra taken with linewidths of about 50 MHz. The Nb hyperfine structure is impressively wide in both states, but particularly so in X 3Δ where one of the unpaired electrons occupies a σ orbital derived from the metal 5s orbital. The electron spin and hyperfine structures do not follow the expected case (aβ ) coupling because of extensive second order spin-orbit effects. It is shown that the asymmetry in the spin–orbit structure of X 3Δ is explained almost quantitatively by interaction with a 1 Δ state from the same electron configuration (which lies at 5197 cm−1); also cross terms between the spin–orbit and Fermi contact interactions in the matrix element 〈3Δ2||H||1Δ〉 produce a large correction to the apparent coefficient of the I⋅L magnetic hyperfine interaction in X 3Δ2. The hyperfine structure in a triplet state turns out to be extremely sensitive to the details of the electron spin coupling, and reversals in the sense of the hyperfine structure in the 3Φ4–3Δ3 and 3Φ2–3Δ1 subbands are shown to be consistent with the3Δ state being a regular spin–orbit multiplet (A〉0). Particular care has been taken with the calibration, which has meant that extra terms have needed to be added to the magnetic hyperfine Hamiltonian to account for the spin–orbit distortions: instead of the usual three parameters needed in case (aβ ) coupling, the B 3Φ state has required four parameters and the X 3Δ state has required five. The model explains the data very well, and the standard deviation in the least-squares fit to more than 1000 hyperfine line frequencies was 0.000 58 cm−1 (17 MHz).
    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 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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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 3320-3328 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An apparatus has been constructed to produce metal compounds using laser ablation and to investigate their rotational spectra with a microwave Fourier transform (MWFT) cavity spectrometer. The first three such compounds that have been studied are silver chloride, aluminum (I) chloride, and copper (I) chloride, produced by ablation of silver, aluminum, and copper rods in the presence of chlorine gas, using a Q-switched Nd:YAG laser (532 nm). The high resolution and sensitivity available with the MWFT cavity spectrometer have permitted the first determination of nuclear spin–rotation coupling constants for AlCl and CuCl. These constants have been used to examine the electronic structures of the molecules. Values of the rotational and nuclear quadrupole coupling constants have also been improved for the three metal chlorides.
    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 99 (1993), S. 6336-6344 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed examination of the structure of the 4Δi ground state of gaseous CoO has been carried out from analysis of the electronic spectrum near 6300 A(ring), using intracavity dye laser and wavelength-resolved fluorescence methods. The intracavity experiments have given the details of the hyperfine structure of the two lowest spin–orbit components at sub-Doppler resolution, permitting the hyperfine parameters, a=0.02295 cm−1 and (b+c)=−0.01117 cm−1, to be derived; from the negative value of the contact interaction the electron configuration is established as (4sσ)2(3dδ)3(3dπ)2. The wavelength-resolved fluorescence experiments have given the relative positions of the four spin–orbit components of the X 4Δi state to ±0.3 cm−1. Based on these measurements, a pair of subbands sharing a common electronic upper level, but with the Ω=5/2 and 7/2 components of the ground state as lower levels, has been recognized. Rotational analysis of Doppler-limited intracavity spectra of these two subbands has given an accurate value for the Ω=5/2–7/2 separation as 304.321±0.007 cm−1.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 6168-6182 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The laser excitation spectrum of tungsten methylidyne, WCH, has been recorded in the 12 000–15 400 cm−1 region. A total of 14 vibronic bands of WCH and 16 bands of WCD have been observed in this region. Rotational analysis shows that the ground state is X˜3/2(2Δ), with the substitution structure r0(W≡C)=1.73665 A(ring) and r0(C–H)=1.0765 A(ring). The excited vibronic levels have been assigned, on the basis of their WCH/WCD isotope shifts and their wavelength resolved fluorescence patterns, to three electronic states, A˜3/2(2Δ), B˜1/2(2Π), and C˜5/2(2Φ), at 12 090, 13 392, and 14 110 cm−1, respectively. The wavelength resolved fluorescence spectra have also established the low-lying vibrational levels of the ground state. The ground state bending fundamental lies at 660 cm−1, while the W–C stretching frequency is 1006 cm−1; the corresponding frequencies in WCD are 501 cm−1 and 953 cm−1, respectively. No evidence for the C–H stretching frequency has been found. Emission has also been observed to a low-lying electronic state, 813 cm−1 above the X˜3/2 state. The pattern of rotationally resolved emission to this state clearly indicates that it is a 4Σ1/2 state. Its bending frequency is 612 cm−1, and its W–C stretching frequency is 971 cm−1, indicating a slightly longer bond length than in the X˜3/2 state. High resolution cw laser spectra of the (0,0) bands of the two lowest excited electronic states [A˜3/2(2Δ) and B˜1/2(2Π)] reveal a small splitting of the four principal tungsten isotopes (182W, 183W, 184W, and 186W) which serves to confirm the presence of tungsten in the carrier. Hyperfine splitting associated with the 183W nucleus (I=1/2) has been observed for the (0,0) band of the A˜3/2−X˜3/2 system, allowing the electron configuration of the ground state to be elucidated. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 31-38 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ν2 infrared fundamental of the transient molecule formyl chloride, HCOCl, has been recorded at high resolution. Detailed assignments of the rotational structure have been made for both HCO 35Cl and HCO 37Cl. The ν2 band, whose origin is at 1784.1377 cm−1 in HCO 35Cl, is predominantly A type with a very weak B-type component. Numerous excited state perturbations occur throughout the band, caused mainly by ||ΔKa||=2 Fermi resonance and ||ΔKa||=1 Coriolis interactions with the 3151 vibrational state. Even though no "extra'' lines resulting from the perturbations could be assigned, a complete analysis of the perturbed rotational structure has been possible. Accurate molecular constants for both the "bright'' perturbed 21 state and the "dark'' 3151 perturbing state have been obtained, using a Hamiltonian which includes both the Fermi and Coriolis interactions; only two interaction parameters are needed, one for each mechanism. Further perturbations at high Ka are assigned to Coriolis interactions with the 5261 level.
    Type of Medium: Electronic Resource
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  • 10
    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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