A combined experimental and theoretical study of the Ti2 + N2O reaction.

The reactivity of diatomic titanium with nitrous oxide has been studied in solid neon. Two molecules with the same Ti2-N2O stoichiometry are identified from concentration, temperature, and irradiation effects. The more stable one is characterized by five fundamental vibrational transitions located below 1000 cm(-1), the high frequency one at 946 cm(-1) corresponding to a pure TiO stretching mode. Its structure, a rhombus OTiNTiN with the extra O atom fixed on one Ti, is confirmed by quantum chemical calculations, at the CCSD(T) level, which predict a Cs structure in the singlet state with a Ti-O bond length close to 1.66 Å, two nonequivalent Ti-N distances close to 1.94 and 1.75 Å, and a OTiTi angle of 119.2°. The second Ti2-N2O molecule, only observed after annealing, is easily converted into the first one upon irradiation above 12 000 cm(-1) and its kinetics of photoconversion allows vibrational transitions to be identified. The strongest one located at 2123.4 cm(-1) characterizes an N-N stretching mode. Corresponding ab initio calculations complete this picture with details on the electronic structure and allow us to identify a most adequate density functional to describe the spectroscopic properties of the studied species in a simpler broken-symmetry open-shell DFT context. The theoretical results predict the existence of a metastable product OTi2N2 and correctly account for the observed spectra of the various isotopic varieties.

Pd(2)N(2), a proteiform molecule: Matrix isolation spectroscopy and density functional theory calculations.

The formation of Pd(2)N(2) from the cocondensation of effusive beams of Pd and N(2) in neon and argon matrices is evidenced by absorptions in the range of 2200-1800 cm(-1). In argon, selective irradiation in the near-infrared and visible ranges leads to interconversions between three structures, distinguished by the stretching frequency of the diatomic N(2): Bridged T-shaped (nu(NN) at 1990 cm(-1)), side on (nu(NN) at 2178 cm(-1)) and parallel (nu(NN) at 1823 cm(-1)). For the first two structures, the nu(NN) mode is also accompanied by another signal below 500 cm(-1). An extra feature close to 490 cm(-1), not sensitive to irradiation at lambda(irr)>400 nm and also assignable to a molecule with the same Pd:N(2) stoichiometry (2:1), corresponds to a centrosymmetrical Pd-N-N-Pd structure with an inactive nu(NN) mode close to 2141 cm(-1), as deduced from the observation of a weak signal close to 2630 cm(-1) associated with this species and assignable to the combination nu(NN)+nu(PdN). All these experimental data and their structural implications are fully supported by theoretical calculations [density functional theory (DFT)]. On the basis of this comparative study, we have obtained a reliable theoretical description of the spectroscopic data using the metageneralized gradient approximation functional within the unrestricted DFT (UDFT) formalism for all spin multiplets. We have also searched a stable electronic solution for each multiplet (particularly for the singlet state), in order to account for the nondynamic correlations.

Rovibrational and dynamical properties of the hydrogen bonded complex (CH2)2S-HF: a combined free jet, cell, and neon matrix-Fourier transform infrared study.

Fourier transform infrared spectra of the nu(s) (HF stretching) band of the (CH(2))(2)S-HF complex have been recorded at 0.1-0.5 cm(-1) resolution in a cooled cell, in a supersonic jet expansion seeded with argon and in a neon matrix at 4.5 K. The combination of controlled temperature effects over a range of 40-250 K and a sophisticated band contour simulation program allows the separation of homogeneous and inhomogeneous contributions and reveals significant anharmonic couplings between intramolecular and intermolecular vibrational modes similar to our previous work on (CH(2))(2)S-DF. The sign of the coupling constants is consistent with the expected strengthening of the hydrogen bond upon vibrational excitation of HF which also explains the observed small variations of the geometrical parameters in the excited state. The analysis of sum and difference combination bands involving nu(s) provides accurate values of intermolecular harmonic frequencies and anharmonicities and a good estimate of the dissociation energy of the complex. Frequencies and coupling parameters derived from gas phase spectra compare well with results from neon matrix experiments. The effective linewidth provides a lower bound for the predissociation lifetime of 10 ps. The comparison between effective linewidths and vibrational densities of states for (CH(2))(2)S-HF and -DF complexes highlights the important role of intramolecular vibrational redistribution in the vibrational dynamics of medium strength hydrogen bonds.