[en] The theory of large angle scattering in chemically reactive systems using parametrized S matrix models is investigated. Calculations of the large angle scattering are carried out for three new parametrizations, in addition to one that has been used previously. All parametrizations are of the smooth step function type, although their analytic structure in the complex angular momentum plane is completely different. Both meromorphic and non-meromorphic parametrizations are employed. Large angle interference effects are found for all parametrizations provided the opacity function is sufficiently black and the transition from absorbency to transparency is sufficiently rapid. (Auth.)

[en] Traditional applications of the Judd-Ofelt (JO) theory to the analysis of the Eu3+ optical spectra make use of the emission transitions originating from the 5D0 manifold. In the present paper, we report an alternative method of evaluating the JO intensity parameters from the Eu3+ emission spectra based on the 5D1 → 7F0,1 transitions. The reduced matrix elements of the unit tensor operators are re-calculated for the 5D0,1,2 → 7F0,1,…,6 Eu3+ transitions in the intermediate coupling approximation using the average electrostatic and spin-orbit coupling parameters. The suggested method was tested by analyzing the emission spectra of the Eu3+ doped GdAlO3, LaF3, NaYF4, Y2O3, ZrO2, YNbO4, ZBLA and PIGLZ hosts. It is shown that the developed method is more accurate for the hosts with relatively high 5D1 level population, which emphasizes its high potential and applicability. In addition to the JO analysis, the CIE chromaticity coordinates are calculated for the investigated spectra. © 2019 Elsevier B.V.

[en] In a crossed molecular beam experiment the nonreactive differential scattering of K by Br₂ has been measured at several laboratory kinetic energies below 10 eV. The experimental angular distributions have been analyzed with the aid of trajectory surface hopping calculations, which are partly in (qualitative) accord with angle, with a 'reduced' value tausub(c), that increases with can be divided into two angular regions, separated by a critical angle, with a ''reduced'' value tausub(c), that increases with the collision energy. The critical angle is related to a critical impact parameter bsub(c), which is determined by the crossing radius Rsub(c) of the potential surfaces involved. (Auth.)

[en] The distorted wave and the Bernstein and Kramer approximations are investigated and compared to close coupling calculations. Analytic expressions are derived for reorientation cross sections, considering elastic small angle scattering. (Auth.)

[en] The collision induced dissociation (CID) process in dilute mixtures of shock heated O₂-Ar and HCl-Ar is investigated. The dissociation is assumed to occur from all vibrational levels. Numerical calculations are presented for the steady state dissociation rate constants at infinite dilution for both the truncated harmonic oscillator (THO) and Morse oscillator (MO) models. The effect of vibration-vibration (V-V) energy transfer processes on the dissociation is also investigated by calculating the steady state rate constants as a function of composition up to 20% of the diatom in these mixtures at 3500 K, 5000 K and 8500 K. The vibration-translation (V-T) energy transfer probabilities are obtained using SSH theory in the case of O₂ and Moore's theory in the case of HCl, and the V-V energy transfer probabilities are obtained using SSH theory in both the cases. The 'vibrational bias' parameter lambda, characterizing the CID probability, has been varied to fit the experimental data. The study shows that the effect of V-V transitions is dependent on the extent of depletion and the relative magnitudes of the V-V and V-T transition rates. Thus there is no effect on the rate in O₂-Ar while the rate is enhanced at 3500 K and 5000 K in HCl-Ar mixtures. (Auth.)

[en] The collinear collision of two diatomic molecules is studied. Six different systems - namely N₂ + N₂, N₂ + CO, N₂ + OC, N₂ + O₂, H₂ + H₂ and H₂ + HBr - are selected as samples and compared to each other. In addition, the effect of anharmonicity on the vibrational excitation is investigated. Exact quantum-mechanical transition probabilities are calculated, the Morse and harmonic binding potentials being considered in each case. It is shown that anharmonicity often decreases the TV transition probabilities by a large factor, whereas it has only a small effect on VV transition probabilities. The results are interpreted on the basis of previous ideas on atom-diatom and diatom-diatom collinear collisions. (Auth.)

[en] Conditions for population inversion in laser pumped polyatomic molecules are described. For systems which exhibit metastable vibrational population distributions, large, long lived inversions are possible even when the vibrational modes are strongly coupled by rapid collisional vibration-vibration (V-V) energy transfer. Overtone states of a hot mode are found to invert with respect to fundamental levels of a cold mode even at V-V steady state. Inversion persists for a V-T/R relaxation time. A gain of 4 m^-1 for the 2ν₃ → ν₂ transition in CH₃F (lambda approx. 15.9 μ) was found assuming a spontaneous emission lifetime of 10 s for this transition. General equations are derived which can be used to determine the magnitude of population inversion in any laser pumped, vibrationally metastable, polyatomic molecule. A discussion of factors controlling the population maxima of different vibrational states in optically pumped, V-V equilibrated metastable polyatomics is also given. (orig./WL)

[en] The proton formation by dissociative electroionization of methane has been investigated in the energy range of 25-40 eV. The kinetic energy-versus-appearance energy shows five different H⁺ producing processes respectively at 26.3 +- 0.2 eV, 26.9 +- 0.2 eV, 29.4 +- 0.3 eV, 32.7 +- 0.2 eV and 35.7 +- 0.5 eV. These critical energies are discussed in terms of different dissociation channels probably opened through predissociation of doubly excited states of CH⁺₄. On the high energy side of the electron energy range investigated in the present work, the proton would appear through the dissociation of the CH⁺ ion as an intermediate. (orig.)

[en] It is demonstrated under which conditions the competition between autoionization and photoemission can give rise to extra peaks in UV photoelectron spectra. Experiments are performed with atomic oxygen and hitherto unobserved autoionization peaks are reported. (orig.)

[en] Theoretical calculations on relevant portions of the potential surface of the first triplet state of MgH₂ were carried out at the SCF and MCSCF CI level in order to learn more about the detailed mechanism of the reaction Mg(3s3p ³P) + H₂ → MgH + H. It was found that this reaction can proceed with essentially no activation barrier (<= 1.8 kcal/mole) above the reaction's 11 - 12 kcal/mole endothermicity via side-on attack by Mg (³P) of the H-H bond, whereas end-on attack gives rise to a barrier of approx. 14 kcal/mole above the endothermicity. Analysis of the orbital occupancy variations along the C₂sub(v) side-on approach coordinate indicates that Mg⁺ - H^-₂ partial charge-transfer interactions are important. No indication of a bound or metastable triplet state of MgH₂ was found. (orig.)