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High resolution electronic spectra of some new transition metal-bearing molecules Rixon, Scott John


Spectra of zirconium monocarbide (ZrC), zirconium methylidyne (ZrCH) and lanthanum imide (LaNH) are reported for the first time. All species have been produced under jet-cooled conditions by reaction of gaseous metal atoms with methane or ammonia and examined via laser-induced fluorescence. ZrC has several electronic states below 2500 cm-¹ : Χ³Σ⁺ and three ¹Σ⁺ states, which appear to represent all possible arrangements of two electrons in the nearly degenerate 11σ and 12 σ orbitals (from Zr 5sσ + C 2pσ). For Χ³Σ⁺ (r₀ = 1.807 Å), the small spin-spin constant (λ₀ = 0.514 cm-¹) and large Fermi contact parameter of ⁹¹Zr¹²C (I[sub zr] = 5/2) indicate the configuration (11σ)¹(12σ)¹ . The tightly bound a¹Σ⁺ state (T₀ = 187.83 cm-¹, r₀ = 1.739 Å) has the configuration (11σ)², while anomalous vibrational intervals and ¹²C / ¹³C isotope shifts of the other two states reveal their isosymmetry. This orbital scheme also accounts for the complex structure above 16000 cm-¹; identical, strongly interacting manifolds result from promoting either a electron to the same orbital. ZrCH has a ²П - Χ²Σ⁺ electronic system in the visible region analogous to that seen for isoelectronic ZrN, but they otherwise share little similarity. For Χ²Σ⁺, high-resolution rotational analyses give r 0 bond lengths, while dispersed fluorescence has characterised its vibrational structure. Conversely, many details remain unclear for the excited state. Upper state P = Λ+l+Σ values and Zr isotope shifts have been obtained for many subbands of ZrCH and ZrCD; ¹²C / ¹³C shifts have also been determined for some ZrCH bands. Unexpectedly small values of the spin-orbit constant and Zr-C stretching frequency, and the large Renner- Teller splitting in the 010-000 band are believed to be due to strong vibronic coupling with ²Σ and ²Δ states. The electronic structure of LaNH is similar to isoelectronic LaO, with the added complication of vibronic coupling between the Ã²П and B²Σ⁺ states. This is apparent from anomalies in the B²Σ⁺ - Χ²Σ⁺ hyperfine intensity profiles (I [sub La] = 7/2), the Hund's case (a) coupled B²Σ⁺ (0υ₂0) level structure and the large B²Σ⁺ state bending frequency.

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