Experimental observation of TiN12+ cluster and theoretical investigation of its stable and metastable isomers

Abstract

TiN_n⁺ clusters were generated by laser ablation and analyzed experimentally by mass spectrometry. The results showed that the mass peak of the TiN₁₂⁺ cluster is dominant in the spectrum. The TiN₁₂⁺ cluster was further investigated by photodissociation experiments with 266, 532 and 1064 nm photons. Density functional calculations were conducted to investigate stable structures of TiN₁₂⁺ and the corresponding neutral cluster, TiN₁₂. The theoretical calculations found that the most stable structure of TiN₁₂⁺ is Ti(N₂)₆⁺ with O_h symmetry. The calculated binding energy is in good agreement with that obtained from the photodissociation experiments. The most stable structure of neutral TiN₁₂ is Ti(N₂)₆ with D_3d symmetry. The Ti–N bond strengths are greater than 0.94 eV in both Ti(N₂)₆⁺ and its neutral counterpart. The interaction between Ti and N₂ weakens the N–N bond significantly. For neutral TiN₁₂, the Ti(N₃)₄ azide, the N₅TiN₇ sandwich structure and the N₆TiN₆ structure are much higher in energy than the Ti(N₂)₆ complex. The DFT calculations predicted that the decomposition of Ti(N₃)₄, N₅TiN₇, and N₆TiN₆ into a Ti atom and six N₂ molecules can release energies of about 139, 857, and 978 kJ mol⁻¹ respectively.