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High resolution spectroscopy of niobium nitride and vanadium oxide

University of British Columbia

This thesis reports the spectroscopic studies of two gaseous molecules, niobium nitride (NbN) and vanadium oxide (VO). The ³∏ — ³∆ electronic transition of NbN was recorded by laser-induced fluorescence at Doppler-limited resolution as well as at sub-Doppler resolution. Two almost identical branch features are observed in the ³∏₀ — ³∆₁ sub-band because the A-doubling in the ³∏₀ sub-state is large and almost J-independent. The ³∏₁ — ³∆₂ transition is shifted 600 cm⁻¹ to the red of its central first-order position as a result of very large second-order spin-orbit interaction effects. The shift is believed to be caused principally by the coupling of the ³∏₁ component with the ¹∏ state from the same electron configuration, with a smaller contribution from coupling of the ³∆₂ component of the ground state with the low-lying ¹∆ state. The ³∏ and ¹∏ states are unusual in that their zero-order energies are calculated to be within 100 cm⁻¹, based on the newly observed ¹∏₁ - ³∆₂ (1,0) transition; this means that they form a very fine example of a "super-multiplet", where the spin-orbit effects within and between the states of a particular electron configuration are larger than their separations. The spin-orbit interactions are so extensive that the fine structure can only be fitted using effective rotational and hyperfine Hamiltonians for the individual sub-states, as in case (c) coupling. From the determined hyperfine constants h and C⍳ for the three ³∏(v — 0) components, the Fermi contact constant b was found to be negative, which is consistent with the configuration πδ. Rotational analysis gave the ³∏ and ³∆ bond lengths as 1.6705 Å and 1.6622 Å, respectively. The near-infrared electronic system of VO has been recorded in emission at Doppler-limited resolution with the 1-m FT spectrometer at Kitt Peak National Observatory. The spectrum in the 4000-14000 cm⁻¹ region consists of numerous transitions with most of them extensively analyzed. Two isolated sub-bands at 7200 cm⁻¹ have been assigned as the two spin components of a ²∏ — ²∆ transition and rotationally analyzed. The rotational constant for the lower state is found to be larger than that for the σδ² X ⁴∑⁻ ground state, indicating that the ²∆ state arises from the electron configuration σ²δ. The configuration assignment was confirmed by the derived spin-orbit coupling constant for the ²∆ state. Similar reasoning applied to the ²∏ upper state suggests that it may arise from the configuration σ²π, though the preliminary study of the hyperfine structure argues against this assignment.

Text

2010-08-30

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http://hdl.handle.net/2429/27961

Chemistry

University of British Columbia

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