Kjerbramsen6601

Finally, we give an outlook for promising directions which may help address the existing issues in the current framework of deep molecular modeling.Collisional transition processes in thermal unimolecular reactions are modeled by collision frequency, Z, and probability distribution function, P(E, J; E', J'), which describes the probabilities of collisional transitions from the initial state specified by the total energy and angular momentum, (E', J'), to the final states, (E, J). The validity of the collisional transition model, consisting of Z and P(E, J; E', J'), is assessed here for the title reaction. The present model and its parameters are derived from the moments of transition probabilities calculated by classical trajectory simulations. The model explicitly accounts for coupling between the energy and angular momentum transfer and the dependence of transition probability on the initial state. The performance of the model is evaluated by comparing the rate constants calculated by solving the two-dimensional master equation with those obtained from the classical trajectory calculations of the sequence of successive collisions. The rate constants are also compared with available experimental data. The present collisional transition model is found to perform fairly well for predicting the pressure-dependent rate constants. The uncertainty in the prediction and sensitivities of the rate constants to the model parameters are discussed. A simplified version of the model is proposed, which performs as well as the full model. The simplifications and robust procedures for calculating the model parameters are described.No direct method for estimating the individual O-H···O hydrogen bond (H-bond) energies in water clusters (W n ) exists in the literature. selleck chemicals In this work, we propose such a direct method based on the molecular tailoring approach, which also enables the estimation of the cooperativity contributions. The calculated H-bond energies at MP2(full)/aug-cc-pVTZ and CCSD(T)/aug-cc-pVDZ levels for W n , n = 3 to 8, agree well with one another and fall between 0.3 and 11.6 kcal mol-1 with the cooperativity contributions in the range of -1.2 and 7.0 kcal mol-1. For gauging the accuracy of our H-bond energies for a cluster, the H-bond energy sum is added to the sum of monomer energies, and the results are compared with the respective total energy. These two values agree with each other to within 8.3 mH (∼5 kcal mol-1), testifying the accuracy of our estimated H-bond energies. Further, these H-bond strengths show a good correlation with the respective O-H stretching frequencies and the molecular electron density values at the (3, -1) O-H···O H-bond critical point.We have used quantum chemistry computations, in conjunction with isodesmic-type reactions, to obtain accurate heats of formation (HoFs) for the small fullerenes C20 (2358.2 ± 8.0 kJ mol-1), C24 (2566.2 ± 7.6), and the lowest-energy isomers of C32 (2461.1 ± 15.4), C42 (2629.0 ± 20.5), and C54 (2686.2 ± 25.3). As part of this endeavor, we have also obtained accurate HoFs for several medium-sized molecules, namely 216.6 ± 1.4 for fulvene, 375.5 ± 1.5 for pentalene, 670.8 ± 2.9 for acepentalene, and 262.7 ± 2.5 for acenaphthylene. We combine the energies of the small fullerenes and previously obtained energies for larger fullerenes (from C60 to C6000) into a full picture of fullerene thermochemical stability. In general, the per-carbon energies can be reasonably approximated by the "R+D" model that we have previously developed [Chan et al. J. Chem. Theory Comput. 2019, 15, 1255-1264], which takes into account Resonance and structural Deformation factors. In a case study on C54, we find that most of the high-deformation-energy atoms correspond to the sites of the C-Cl bond in the experimentally captured C54Cl8. In another case study, we find that C60 has the lowest value for the maximum local-deformation energy when compared with similar-sized fullerenes, which is consistent with its "special stability". These results are indicative of structural deformation playing an important role in the reactivity of fullerenes.Energetic conditions that are required for favorable singlet exciton fission, an intermolecular electron correlation effect, are studied with relativistic quantum chemical methods as to investigate the effect of a varying fine-structure constant. Ethylene and derivatives thereof serve as simple model systems, whereas pentacene and perfluoropentacene, which display singlet exciton fission experimentally, are used as specific examples for possible applications. Effects are estimated to be small in this class of compounds, but substitution with heavier halogens might lead to oppositely shifting energy levels and thereby improved sensitivity in narrow resonance situations.An accurate quantum chemical modeling of 125Te NMR spectra is of great importance in the NMR structural assignment for real-life tellurium compounds, which represent a growing interest in organic and inorganic chemistry nowadays. This work reports a computationally modest combined approach based on the density functional theory only, which provides an excellent accuracy against the experiment and can be effectively applied for the routine large-scale calculations of tellurium chemical shifts. The role of solvent, vibrational, and relativistic corrections has been thoroughly investigated. Special attention was paid to the effect of taking into account the scalar relativistic effects during the geometry optimizations on the calculated tellurium chemical shifts.1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), which forms weak hydrogen bonds despite the high basicity caused by its hindered structure, was used to investigate tautomer formation via excited-state intermolecular proton-transfer (ESPT) reactions. The kinetics of the ESPT reactions of anthracen-2-yl-3-phenylurea (2PUA) in the presence of DBU were compared to that observed for the acetate anion (Ac) using time-resolved fluorescence measurement. Based on the association constants in the ground state, the intermolecular hydrogen bond between 2PUA and DBU was less stable than the bond between 2PUA and Ac due to steric hindrance and the geometry of the hydrogen bond. In the fluorescence spectra, 2PUA-DBU displayed prominent tautomeric emission in chloroform (CHCl3), whereas 2PUA-Ac exhibited distinct tautomeric emissions in dimethyl sulfoxide (DMSO). Kinetic analysis revealed that the rate constant of the ESPT reaction of 2PUA-DBU remarkably decreased when the proton-accepting ability of the solvent increased whereas the reaction of 2PUA-Ac was linked to the solvent polarity rather than proton-accepting ability. These results indicated that moderate hydrogen bonds due to steric hindrance were influenced by the type of solvent present, particularly if the solvents exhibited proton-accepting capabilities like DMSO. This, in turn, affected the rate constant of tautomer formation.Following a nuclear accident, radioactive iodine causes great concern to public health and safety. Organic iodide, because of its ability to escape reactor containment building and high environmental mobility, constitutes a predominant fraction of airborne radioiodine at places far away from the accident site. As the iodine released from a reactor core is inorganic iodine, it is vital to understand the mechanism of organic iodide formation inside reactor containment. In this context, we investigated the surface prevalence and adsorption of various inorganic iodines, I-, I3-, and IO3-, at a nuclear paint (used in nuclear installations) monolayer-water interface, mimicking the painted inner walls of an accident-affected containment building that are exposed to the iodine-containing condensed water layer. Vibrational sum frequency generation (VSFG) measurements in the OH and CH stretch regions reveal that the paint-water interface changes its charge characteristics with the pH of the water that affects the degree of interaction with the iodine species. At the acidic condition (bulk pH 9.5), the paint becomes net neutral and weakly interacts with the iodine species. These interactions change the conformation of the paint such that its hydrophobic alkyl groups orient increasingly away from the aqueous phase. The order of adsorption increases as IO3- less then I- less then I3- for the different iodine species studied.Trivalent europium (Eu3+) complexes are attractive materials for luminescence applications if energy transfer from antenna ligands to the lanthanide ion is efficient. However, the microscopic mechanisms of the transfer remain elusive, and fundamental physical chemistry questions still require answers. We track the energy transfer processes in a luminescent complex Eu(hfa)3(DPPTO)2 (hfa, hexafluoroacetylacetonate; DPPTO, 2-diphenylphosphoryltriphenylene) using time-resolved photoluminescence spectroscopy. In addition to the conventional energy transfer pathway through the T1 state of the ligands, we discovered ultrafast energy transfer pathway directly from the singlet excited states of the ligands to the 5D1 state of Eu3+. The short time scale of the energy transfer (3 ns, 200 ns) results in its high photoluminescence quantum yield. The discovery of the distinct energy transfer pathways from a single chromophore is important for establishing design strategies of luminescent complexes.The abnormal level of cysteine (Cys) in the human body will cause a series of diseases, and the study of the sensing mechanism is of great significance for the design of efficient fluorescent probes. Here, we used time-dependent density functional theory to study the sensing mechanism of a newly synthesized imidazo [1,5-α] pyridine-based fluorescent probe (MZC-AC) for the detection of Cys, which is proposed to be designed based on excited-state intramolecular proton transfer (ESIPT). We first show that the fluorescence quenching mechanism of MZC-AC is due to a nonclassical photoinduced electron transfer (PET) process in which the curve crossing between local excited and charge-transfer states is observed and the acrylate group acts as an electron acceptor. When the acrylate group is replaced by the hydroxyl group due to the reaction between MZC-AC and Cys, the PET is off and a significant fluorescence enhancement of the formed MZC is observed. Our theoretical results indicate that the fluorescence enhancement mechanism of MZC is not based on the ESIPT. link2 The calculated potential energy curve along the proton transfer pathway shows that the electronic energy of MZC-keto is larger than that of MZC-enol. Moreover, the computed emission energy of MZC-enol is closer to the experimental data than that of MZC-keto. The experimentally observed large Stokes shift was ascribed to the intramolecular charge transfer character of the first excited state of MZC. Our theoretical results can explain well the fluorescence behavior of MZC-AC and MZC and invalidate the experimentally proposed ESIPT mechanism of MZC.We report calculations for the elastic collision of low-energy positrons by acetone (C3H6O). For this purpose, the Schwinger multichannel method was used in the static plus polarization approach to calculate cross sections in the energy range from 10-4 to 10 eV. link3 Acetone is a polar molecule, and the effect of the long-range dipole interaction was taken into account through the Born-closure scheme. Our integral cross section was compared with the experimental total cross section results available in the literature, which do not agree among themselves below 2 eV. Our results agree qualitatively well with the most recent experimental data available in all energy regions. Particularly, below the positronium formation channel threshold, when the experimental data are corrected because of the angular resolution of the apparatus, the quantitative agreement is improved.