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

Abstract

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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