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The gas-phase decomposition kinetics of isopropyl acetate (IPA) and its methyl, bromide and hydroxyl derivatives into the corresponding acid and propene were investigated using density functional theory (DFT) with the omega B97XD and M06-2x functionals, as well as the benchmark CBS-QB3 composite method. Transition state theory (TST) and RRKM theory calculations of rate constants under atmospheric pressure and in the fall-off regime were used to supplement the measured energy profiles. The results show that the formation of propene and bromo-acetic acid is the most dominant pathway at the CBS-QB3 composite method, both kinetically and thermody-namically. There was a good agreement with experimental results. Pressures greater than 0.01 bar, corresponding to larger barrier heights are insufficient to ensure saturation of the measured rate coefficient when compared to the RRKM kinetic rates. Natural bond orbitals (NBO) charges, bond orders, bond indices, and synchronicity parameters all point to the considered pathways taking place via a homogenous, first-order concerted, as well as an asynchronous mechanism involving a non-planar cyclic six-membered transition state. The calculated data exhibit that the elongation of the C alpha-O bond length and subsequent polarization of the C alpha thorn delta...O-delta bond is the rate-determining step of the considered reactions in the cyclic transition state, which appears to be involved in this type of reaction. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors dedicate this manuscript to the soul of Prof. Dr. Ahmed El-Nahas, the father of computational chemistry in Egypt, who recently died in an accident. May his soul rest in peace.

The potential energy surface (PES) of aniline was comprehensively investigated at different levels in this paper. The stable conformer of aniline has CS point group while the transition states possess CS and C2V symmetries. The computed transition states of aniline are highly dependent on the level of the computations including Hartree-Fock, Density functional and Moller–Plesset perturbation theories. The electric dipole moment of the molecule varies by the rotation of the amino group with respect to the phenyl plane, while in the range of 60–120 degrees, the changes of the dipole moment is not noticeable.

A comprehensive study of the He (I) ultra-violet photoelectron spectra of fluorene, carbazole and dibenzofuran is presented with the aid of one-particle Green’s Function calculations employing the outer-valence Green’s Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with Dunning’s correlation consistent basis sets of double and triple zeta quality (cc-pVDZ, cc-pVTZ). Extrapolations of the ADC(3) results for the outermost one-electron π-ionization energies to the cc-pVTZ basis set enable theoretical insights into He (I) measurements within ∼0.15 eV accuracy, up to the σ-ionization onset. The lower ionization energy of carbazole is the combined result of mesomeric and electronic relaxation effects. OVGF/cc-pVDZ or OVGF/cc-pVTZ pole strengths smaller than 0.85 systematically corroborate a breakdown of the orbital picture of ionization at the ADC(3) level. Comparison is made with calculations of the lowest doublet–doublet excitation energies of the radical cation of fluorene, by means of time-dependent density functional theory (TDDFT).

An extensive study of the valence electronic structure, ionization spectrum and electron momentum distributions of pyrimidine is presented, on the ground of accurate calculations of one-electron and shake-up ionization energies and of the related Dyson orbitals, using one-particle Green’s Function theory in conjunction with the third-order Algebraic Diagrammatic Construction scheme [ADC(3)]. Comparison is made with results obtained from standard (B3LYP) Kohn–Sham orbitals and recent measurements employing Electron Momentum Spectroscopy. Quantitative insights into the experimental momentum distributions are amenable without resorting to any empirical rescaling of pole strengths, provided band overlaps and relaxation effects are properly accounted for.