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Notes: The conical intersection regions on the potential energy functions of the valence excited 1,3Σu−, 1,3Δu, 3Σu+, and 1,3Πg states of CO2 have been investigated by ab initio calculations. Using large scale multireference configuration interaction the ordering of the lowest valence excited states of CO2 has been calculated to be 3B2, 3A2, 1A2 followed by 1B2. All these states have bent equilibrium structures and lie energetically below their dissociation asymptotes. The near equilibrium parts of the potential energy functions have been mapped in three dimensions by multiconfiguration self-consistent field calculations. The 1,3B2 and 1,3A2 states differ in their equilibrium angles (118° and 127°, respectively), and have much longer equilibrium distances (around 1.26 A(ring)) than the electronic ground state. Anomalously low values of ca. 800 cm−1 have been calculated for the wave number of the antisymmetric stretching vibrations of the 1A2, 3B2, and 1B2 states. The crossings between the bent valence excited states in the geometry region 90°≤αOCO≤150° and 1.1 A(ring)≤RCO≤1.4 A(ring) have been located.

Notes: The potential energy curves of the two lowest 2Σ+ (X,B) and the two lowest 2Π (A,C) electronic states of the AlF+ and AlCl+ molecular ions have been calculated using highly correlated multireference configuration interaction (MR-CI) wave functions. It is found that both 2Σ+ states and the C 2Πr state are bound, whereas the A 2Πi state is repulsive. Electronic transition moment functions for all six pairs of states of both ions have also been calculated and used for evaluation of the radiative transition probabilities between bound vibrational states. The calculated charge distributions show that the X and C states are dominated by Coulombic attraction between a doubly charged positive aluminum and the singly charged negative halogen ion. The results provide a new assignment of the photoelectron spectra of the neutral AlF. They are also in good agreement with the recently observed optical B–X emission spectra of both molecular ions and C–X bands of AlCl+. The absence of C–X emission of AlF+ is most likely due to predissociation of the C 2Πr state by the repulsive A 2Πi state.

Notes: We calculate the rovibrational structure for the electronic transition of the Ar–OH complex between the ground and first excited electronic states, which correlate asymptotically with Ar(1S0)+OH(X 2Π) and Ar(1S0)+OH(A 2Σ+), respectively. An ab initio potential energy surface is used and the rovibrational states are calculated using a basis set method which couples the electronic spin and orbital angular momentum of the diatomic fragment with the overall rotations and vibrations of the complex. The calculated spectrum is compared with experimental results. In the low-frequency region the spectrum is found to be well ordered and assignment of spectroscopic features in terms of bending and stretching quantum numbers is possible. Close to dissociation, bend–stretch coupling leads to highly mixed states for which such assignments are no longer possible.

Notes: An R-matrix algorithm is developed for executing vibrational predissociation calculations within the Golden Rule approximation. The algorithm is used to calculate vibrational predissociation linewidths and OH product rotational distributions for the quasibound states of Ar–OH (A2 Σ+, v=1). An ab initio potential energy surface obtained with the coupled electron pair approximation is used in the computations. The theoretical results are compared with experiment. The high anisotropy of the system is found to strongly favor vibrational to rotational energy transfer and the product OH (A2 Σ+ , v=0) molecules are produced in highly excited rotational states. Quasibound states associated with excited bending levels are predicted to dissociate more rapidly than those assigned to the ground bend. For metastable states with the same bending quantum number, linewidths are predicted to decrease with increase in the intermolecular stretching quantum number.

Notes: In this letter we report quantum mechanical integral and differential cross sections for the title reactions as calculated on a new ab initio potential energy surface. The calculations, all carried out in the reagents arrangement channel employing negative imaginary potentials, were done within the coupled-states approximation. The final vibrational state-to-state differential and integral cross sections were compared with experiment. Altogether, a very encouraging agreement was obtained. © 1996 American Institute of Physics.

Notes: The dynamics of the F+HD reaction has been studied by means of quasiclassical trajectory calculations on an ab initio potential energy surface (PES) at several collision energies. At the collision energy of 85.9 meV and for the DF+H isotopic channel of the reaction, there is a remarkable agreement between calculated and experimental results, in both the center of mass (c.m.) differential cross sections (DCS) and in the simulation of the laboratory (LAB) time of flight (TOF) and angular distributions (AD). The good agreement also extends to the lower collision energy of 58.6 meV for this channel of the reaction. In contrast, the simulation of the LAB angular distributions for the HF+D channel shows strong discrepancies between theory and experiment at both collision energies, which can be traced back to the absence of a forward peak in the calculated c.m. DCS for HF(v'=3). Simulations made from QCT calculations on other PES with important HF(v'=3) forward scattering contributions also fail to reproduce the overall AD. The theoretical findings and especially the roles of translational energy and initial rotational momentum on the dynamics of this reaction are discussed in terms of the topology of the PES through the analysis of individual trajectories. © 1995 American Institute of Physics.

Notes: Abstract: Different noninvasive techniques for the assessment of the individual fracture risk in osteoporosis are introduced, and the relation between structural properties of high-resolution computed tomography (HR-CT) images of vertebral bodies, their bone mineral density (BMD) and the fracture load is analyzed. In 24 unfractured lumbar vertebrae with different degrees of demineralization from six specimens, the trabecular and cortical BMD was determined using quantitative CT. A lateral X-ray image revealed the number of fractures in the entire spine. A structural analysis of spongy and cortical bone was performed based on the HR-CT images. In the spongiosa, the fractal dimension was calculated as a function of the threshold value. In the cortical shell, the maximum number of clusters of low BMD was determined at varying threshold values. After the CT measurements the vertebrae were excised and compressed until fractured. On the basis of the spongiosa BMD and the number of fractures, 3 cases were found to be severely osteoporotic; the other 3 cases showed osteopenia. The average fracture loads were determined as 3533 N for the non-osteoporotic cases (range 2602–5802 N) and 1725 N for the osteoporotic cases (range 1311–2490 N). The parameters were determined as follows: average spongiosa BMD 115.2 mg/ml (101.8–135.3 mg/ml) for the non-osteoporotic cases, 46.2 mg/ml (34.8–57.6 mg/ml) for the osteoporotic cases; average cortical BMD 285.1 mg/ml (216.4–361.9 mg/ml) for the non-osteoporotic cases, 136.1 mg/ml (142.5–215.2 mg/ml) for the osteoporotic cases; spongiosa structure: average 0.5 (range 0.32–0.75) for the non-osteoporotic cases, average 1.05 (range 0.87–1.24) for the osteoporotic cases; cortical structure: average 81 (range 55–104) for the non-osteoporotic cases), average 136 (range 102–159) for the osteoporotic cases. Single parameters (BMD and structure) and weighted sums of these parameters were correlated with the fracture load, resulting in correlation coefficients of r sBMD= 0.82 (spongiosa BMD), r cBMD= 0.82 (cortical BMD), r sStr=–0.75 (spongiosa structure) and r cStr=–0.86 (cortical structure). The weighted sum of cortical and spongiosa BMD resulted in r BMD= 0.86, of cortical and spongiosa structure in r Str=–0.86. A weighted combination of all four parameters correlates with the fracture load at r 4= 0.89, all correlations being statistically significant (p〈0.0001). The four individual parameters show only a slight overlap between non-osteoporotic and osteoporotic subjects. The high correlation of the cortical BMD and the structural parameter in cortical bone indicates the important contribution of the cortical shell to vertebral stability. A weighted sum of multiple parameters results in a higher correlation with the fracture load and does not show an overlap between the two groups. It is best suited to estimate the individual fracture risk. The presented methods are generally applicable in vivo; and allow an improvement of the diagnosis of osteoporosis compared with the measurement of the BMD alone.