Reactivity of titanium dimer and molecular nitrogen in rare gas matrices. Vibrational and electronic spectra and structure of Ti2N2

Abstract

The reactivity of diatomic titanium with molecular nitrogen has been investigated in rare gas matrices. The formation of Ti₂N₂ from the condensation of effusive beams of Ti and N₂ in neon and argon matrices is observed after sample deposition. Our results also show that the in situ formation results from the spontaneous reaction at 9 K of ground state Ti₂ with N₂. Several low-lying excited states of Ti₂N₂ are also observed between 0.78 and 1.1 eV above the ground state, leading to a complex sequence of interacting vibronic transitions, merging into a broad continuum above 1.25 eV. Observations of Ti¹⁴₂N₂, Ti¹⁵₂N₂ and Ti¹⁴₂N¹⁵N isotopic data enable the determination of all fundamental vibrations in the ground electronic state. Semi-empirical harmonic potential calculations lead to estimates of 3.22 N cm⁻¹ for the Ti–N bond force constant and 90 ± 5° for the bond angles. Comparisons with TiN diatomic data suggest a near square-planar structure with 175 ± 3 pm TiN bond distance. Quantum chemical calculations at various levels indicate a ¹A_g ground state with a Ti–N distance close to 180 pm and 89° for the NTiN bond angle, and give fundamental frequencies in excellent agreement with the experimentally observed values. Further MRCI calculations on all low-lying states enable an interpretation of the complex electronic spectrum in the NIR region.