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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4138-4155 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational and hyperfine analyses have been carried out for the (0,0) bands of the C 3Π–X 3Δ, e 1Π–X 3Δ, and f 1Φ–a 1Δ transitions of gaseous NbN from laser excitation spectra taken at sub-Doppler resolution. The δπ C 3Π and e 1Π states lie only 102 cm−1 apart in zero order but the spin–orbit matrix element between them, which is the sum of the spin–orbit constants for the δ and π electrons, is 698 cm−1; as a result the 3Π1 spin component lies below both the 3Π0 and 3Π2 components, and its hyperfine structure is highly irregular. This irregularity is an extreme example of how cross terms between the spin–orbit interaction and the Fermi contact hyperfine operator alter the apparent value of the hyperfine a constant, the coefficient of I⋅L in the magnetic hyperfine Hamiltonian. Molecular parameters for the C 3Π and e 1Π states have been obtained from a combined fit to the two of them. Including data for the B 3Φ state recorded earlier [Azuma et al., J. Chem. Phys. 91, 1 (1989)], detailed information is now available for all six of the electronic states from the electron configurations σδ and δπ. It has been verified that the spin–orbit/Fermi contact cross terms cause roughly equal and opposite shifts in the hyperfine a constants for the singlet states and the Σ=0 components of the triplet states. After allowing for this effect, it has been possible to interpret the hyperfine a constants in terms of one-electron parameters for the δ and π electrons, in similar fashion to spin–orbit parameters. Wavelength resolved fluorescence, following selective laser excitation of the C 3Π, e 1Π, and f 1Φ states, has led to the discovery of three new electronic states, δ2 c 1Γ, δ2 A 3Σ−, and σ2 b 1Σ+, besides giving the absolute position of a 1Δ. Strong configuration interaction mixing is found to occur between the σ2 b 1Σ+ and δ2 d 1Σ+ states. The low-lying electronic states of NbN are now well understood.
    Type of Medium: Electronic Resource
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