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

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 Oh 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 D3d 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.