Vibrational Spectra and Structures of Ti–N₂O and OTi–N₂: A Combined IR Matrix Isolation and Theoretical Study

The reaction of atomic titanium with nitrous oxide has been reinvestigated using matrix isolation in solid neon coupled to infrared spectroscopy and by quantum chemical methods. Our technique of sublimation of Ti atoms from a filament heated at about 1500 °C allowed the formation of three species: one Ti–N₂O pair of van der Waals (vdW) type characterized by small red shift with respect to N₂O monomer, and two isomers of OTi–N₂ pair where N₂ is in interaction with the OTi moiety either with end-on or side-on structure. Interconversion between these structures has been performed with several wavelengths. In the visible and near-ultraviolet the conversion vdW → OTi-N₂ (end-on) is observed with characteristic times strongly varying according to the wavelength. In the near-infrared the conversion OTi–N₂ (end-on) → OTi–N₂ (side-on) occurs, the vdW species remaining unchanged. These selectivities allow 8, 6, and 4 vibrational transitions to be assigned for vdW, ³[OTi­(η¹-NN)] (end-on), and ¹[OTi­(η²-NN)] (side-on), respectively. Electronic and geometrical structures are also investigated with double-hybrid functionals. It has been shown that the side-on geometry corresponds to the ground state of ¹[OTi­(η²-NN)] in the singlet electronic state. The theoretical vibrational analysis supports well the experimental attributions