Chemiluminescence from the Ba((3)P)+N(2)O-->BaO(A (1)Sigma(+))+N(2) reaction: Collision energy effects on the product rotational alignment and energy release.

Centro Láser de Ciencias Moleculares, INFIQC, and Departamento de Fisicoquímica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
The Journal of Chemical Physics (Impact Factor: 3.12). 01/2010; 132(3):034304. DOI: 10.1063/1.3294880
Source: PubMed

ABSTRACT Both fully dispersed unpolarized and polarized chemiluminescence spectra from the Ba((3)P)+N(2)O reaction have been recorded under hyperthermal laser-ablated atomic beam-Maxwellian gas conditions at three specific average collision energies E(c) in the range of 4.82-7.47 eV. A comprehensive analysis of the whole data series suggests that the A (1)Sigma(+)-->X (1)Sigma(+) band system dominates the chemiluminescence. The polarization results revealed that the BaO(A (1)Sigma(+)) product rotational alignment is insensitive to its vibrational state upsilon(') at E(c)=4.82 eV but develops into an strong negative correlation between product rotational alignment and upsilon(') at 7.47 eV. The results are interpreted in terms of a direct mechanism involving a short-range, partial electron transfer from Ba((3)P) to N(2)O which is constrained by the duration of the collision, so that the reaction has a larger probability to occur when the collision time is larger than the time needed for N(2)O bending. The latter in turn determines that, at any given E(c), collinear reactive intermediates are preferentially involved when the highest velocity components of the corresponding collision energy distributions are sampled. Moreover, the data at 4.82 eV suggest that a potential barrier to reaction which favors charge transfer to bent N(2)O at chiefly coplanar geometries is operative for most of the reactive trajectories that sample the lowest velocity components. Such a barrier would arise from the relevant ionic-covalent curve crossings occurring in the repulsive region of the covalent potential Ba((3)P)cdots, three dots, centeredN(2)O((1)Sigma(+)); from this crossing the BaO(A (1)Sigma(+)) product may be reached through mixings in the exit channel with potential energy surfaces leading most likely to the spin-allowed b (3)Pi and a (3)Sigma(+) products. The variation with increasing E(c) of both the magnitude of the average BaO(A (1)Sigma(+)) rotational alignment and the BaO(A (1)Sigma(+)) rovibrational excitation, as obtained from spectral simulations of the unpolarized chemiluminescence spectra, consistently points to additional dynamic factors, most likely the development of induced repulsive energy release as the major responsible for the angular momentum and energy disposal at the two higher E(c) studied. The results of a simplified version of the direct interaction with product repulsion-distributed as in photodissociation model do not agree with the observed average product rotational alignments, showing that a more realistic potential energy surface model will be necessary to explain the present results.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The chemiluminescent reaction Ba(6s6p (3)P)+N(2)O was studied at an average collision energy of 1.56 eV in a beam-gas arrangement. Ba((3)P) was produced by laser ablation of barium, which resulted in a broad collision energy distribution extending up to approximately 5.7 eV. A series of experiments was made to extract the Ba((3)P) contribution to chemiluminescence from that corresponding to Ba 6s(2) (1)S0 and 6s5d (3)D, which are the other two most populated states in the atomic beam. The fully dispersed polarized chemiluminescence spectra at 400-600 nm from the title reaction were recorded and assigned to a BaO molecule excited in the A (1)Sigma+ level. In addition, the average and wavelength-resolved degrees of polarization associated to the parallel BaO(A (1)Sigma+-->X (1)Sigma+) emission are reported. The analysis of the average polarization degree show that the BaO(A (1)Sigma+) product is significantly aligned, suggesting that the reaction mechanism is predominantly direct. The product rotational alignment was found to depend markedly on the emission wavelength, which revealed a negative correlation with the BaO(A (1)Sigma+) product vibrational state. On the basis of experimental and theoretical investigations on the reactions of N(2)O with both the (1)S0, (3)D, and (1)P1 states of Ba and the lighter group 2 atoms, it is suggested that the Ba((3)P) reaction involves a charge transfer at relatively short reagent separations and that restricted collision geometries at the highest velocity components of the broad distribution are necessary to rationalize the data.
    The Journal of Chemical Physics 08/2007; 127(6):064309. · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The ground state potential energy surface of the nitrous oxide negative ion is characterized and related to that of the neutral molecule by a synergetic theoretical–experimental approach. Abinitio multiconfiguration self-consistent-field/configuration interaction (MCSCF/CI) and other calculations for N2O−(X 2A′) yield the minimum energy geometry (ReNN, ReNO, AeNNO) = (1.222±0.05 A˚, 1.375±0.10 A˚, 132.7±2°), the vibrational frequencies (ν1,ν2,ν3) = (912±100 cm−1, 555±100 cm−1, 1666±100 cm−1), the dipole moment μ =2.42±0.3 D, and other properties. The N2O− molecular ion in the X 2A′ state is found to have a compact electronic wavefunction—one with very little diffuse character. The MCSCF/CI bending potential energy curve from 70° to 180° for the X 1Σ+(1 1A′) state of N2O as well as the bending curve for the X 2A′ state of N2O− are also reported. The dissociation energy D (N2–O−) =0.43±0.1 eV and, thus, the adiabatic electron affinity E.A.(N2O) =0.22±0.1 eV and the dissociation energy D (N–NO−) =5.1±0.1 eV are determined from beam–collision chamber experiments. Corrections are made for both the dispersion in the ion beam and the translational motion of each target gas. The combined theoretical and experimental results yield a vertical electron affinity V.E.A.(N2O) of −2.23±0.2 eV and enable the construction of angular dependent Morse functions to represent the neutral and ionic surfaces. This construction leads to the determination of the minimum intersection locus as (V*, R*NN, R*NO, A*NNO) = (0.67±0.1 eV, 1.18±0.05 A˚, 1.28±0.10 A˚, 154±3°). The predicted activation energy of this critical point with respect to the asymptote O−, N2—0.21±0.1 eV—and the position of the critical point with R*NN well outside of the N2 (v=0) outer turning point imply that the reaction O−+N2↠N2O+e will be strongly facilitated by reagent vibrational excitation.
    The Journal of Chemical Physics 12/1976; 65(12). · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Chemiluminescence from the reactions of Ba ground state 6s2 1S and metastable 6s5d 3D atoms with NO2, N2O, and O3 has been studied under single‐collision conditions. Spectra, chemiluminescence cross sections, and photon yields for production of BaO∗ are reported. In the Ba(3D)+N2O and Ba(1S, 3D)+O3 reactions, a red feature, not previously reported, has been observed and tentatively assigned as BaO D 1Σ+–A 1Σ+ emission. The dynamics of these reactions and the differences between the Ba and lighter alkaline earth atom reactions are discussed.
    The Journal of Chemical Physics 01/1983; 79:5351-5359. · 3.12 Impact Factor

Full-text (2 Sources)

Available from
May 31, 2014