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Laser spectroscopy of some transition metal-containing free radicals Kingston, Christopher Thomas

Abstract

Laser induced fluorescence (LIF) studies have been performed on the transition metal-containing free radicals nickel cyanide (NiCN), niobium oxide (NbO), niobium methylidyne (NbCFf) and tantalum methylidyne (TaCH). All molecules were produced by the reaction of laser-ablated metal atoms with a reactant gas under supersonic jet-cooled conditions. Precise rotational constants and bond lengths have been obtained for the X₁²Δ[sub 5/2] state of NiCN. The vibrational structure "of this state is dominated by a Fermi resonance interaction, as are those of the low-lying X₂²Δ[sub 3/2] and W₁²Π[sub 3/2] states. Four excited electronic states have been identified, showing that the electronic structure of NiCN is remarkably similar to that of NiH. High resolution spectra of NbO have given the rotational and hyperfine constants for the levels v=0-3 of the B⁴Π state. Strong irregularities in the vibrational dependences of these constants can be interpreted in terms of spin-orbit interaction between the B⁴Π state and the f²Π , e²Φ and d²Δ states. The hitherto unknown ⁴Δ state is estimated to lie near 17500 cm⁻¹, from the vibrational dependence of the spin-rotation parameter γ of the B⁴Π state. Thorough vibrational, rotational and hyperfine analyses were performed on the X³Δ[sub I] state of NbCH. The hyperfine widths of this state vary considerably as a result of spinuncoupling. The A³Φ₂ and B³Δ₁ excited states are heavily perturbed, with as many as nine levels appearing where only one is expected, which complicates the vibrational and rotational analyses. Tantalum methylidyne was found to have an X Ω=0⁺ (¹Σ⁺) ground state, with bond lengths r₀(Ta-C)=1.7714 Å and r0(C-H)= 1.080 Å. The rotational lines exhibit unusually large quadrupole hyperfine splittings caused by the nuclear spin, 1=7/2, of the ¹⁸¹Ta nucleus. This effect is normally too small to appear in optical spectra. Interaction between the A Ω=1 (¹Π) and B Ω=0+ (³Π₀[sub +]) states has been identified through the transfer of magnetic hyperfine character to the B state from A.

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