The geometries and infrared spectra of the trivalent metal trisacetylacetonate complexes (M[O2C5H7]3) (M = Sc, Ti, V, Cr, Mn, Fe, Co, Al) have been calculated using nonlocal hybrid density functional theory (DFT) with a split-valence plus polarization basis for the ligand and valence triple-ζ for the metal. These molecules are uncharged, which facilitates the calculations, but at the same time are fairly ionic, resembling biologically important metal complexes with “hard” ligands (O, N). DFT has been widely used to model such complexes, but very few rigorous comparisons have been performed for experimentally well-characterized model compounds. Vibrational spectra are very sensitive to molecular structure and thus constitute an adequate test of the theory. After a mild scaling correction, the calculated frequencies are in excellent agreement with the experimental fundamentals, and the predicted infrared intensities are qualitatively correct. The results allow an unambiguous assignment of the observed infrared spectra; some earlier assignments have been revised. Our results show that current routine theoretical techniques can predict accurate vibrational spectra for this class of compounds. In part I we focus on Fe, Cr, Sc, and Al tris-acetylacetonates; these are high-spin D3 complexes that are expected to present no Jahn−Teller distortion. (Ti, V, Mn, and Co tris-acetylacetonates are treated in part II.) Correlating calculated infrared spectra with experiment should lead to firm structural predictions in these difficult systems.

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The vibrational spectra of the R, β, and δ phases of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) have been investigated by complimentary theoretical and experimental approaches. Density functional theory and the scaled quantum mechanical force-field method have been used to calculate the vibrational spectra of the H 8 C 4 N 8 O 8 molecule in C i and C 2V symmetry conformations in the gas phase. By comparing the calculated molecular vibrational frequencies of the H 8 C 4 N 8 O 8 molecule with the experimental infrared and Raman spectra of HMX crystalline samples, we attempt to assign the intramolecular motions that correspond to the measured bands in the experimental spectra of HMX in R-, β-, and δ-phase crystal lattices. Our analysis of the vibrational spectra verifies that the particular conformation of the H 8 C 4 N 8 O 8 molecule in each crystal lattice of HMX determines, to a great extent, the general pattern of the vibrational spectrum of the crystal lattice. We also compare our detailed motion assignments with the general assignments proposed in previous experimental work. Good agreement is found between the calculated geometry of the H 8 C 4 N 8 O 8 molecule in the C i symmetry conformation and the experimental geometry of molecules in the β-phase lattice of HMX and between the calculated geometry of the H 8 C 4 N 8 O 8 molecule in the C 2V symmetry conformation and the experimental geometry of molecules in the Rand δ-phase lattices of HMX.

The reaction of OH radicals with olefins is known to be important in atmospheric chemistry. From experimental data a global mechanism has been proposed, but the regioselectivity of the products is uncertain. In this work, the OH–propene–O2 reaction has been studied with ab initio molecular orbital techniques. Reactants, transition structures, intermediate species and products are optimized at the UMP2/6‐31G** level for the two possible addition paths. In the first step, OH adducts are obtained with the OH radical linked to either the terminal or the central C atoms. Consideration of the second step, the addition of O2, is required to explain the observed experimental data. The selectivity of the total reaction is found to be temperature and pressure dependent, but independent of the preferred site for the OH attack. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 29–36, 1999

The reaction of OH radicals with olefins is known to be important in atmospheric chemistry. From experimental data a global mechanism has been proposed, but the regioselectivity of the products is uncertain. In this work, the OH-propene-O 2 reaction has been studied with ab initio molecular orbital techniques. Reactants, transition structures, intermediate species and products are optimized at the UMP2/6-31G** level for the two possible addition paths. In the first step, OH adducts are obtained with the OH radical linked to either the terminal or the central C atoms. Consideration of the second step, the addition of O 2 , is required to explain the observed experimental data. The selectivity of the total reaction is found to be temperature and pressure dependent, but independent of the preferred site for the OH attack.