Ab Initio Mechanism and Multichannel RRKM−TST Rate Constant for the Reaction of Cl(²P) with CH₂CO (Ketene)

The potential energy surface for the most important pathways of the reaction between Cl(2P) and ketene has been studied using the ab initio G2(MP2) method. A variety of possible complexes and saddle points along the minimum energy reaction paths have been characterized at the UMP2(full)/6-31G(d,p) level. The calculations reveal that the addition−elimination mechanism dominates the Cl + CH2CO reaction and the direct hydrogen abstraction pathway is negligible. It is interesting to note that the addition reaction starts by the formation of a p−π complex (PπC), and subsequently the chlorinated acetyl radical CH2ClCO(2A‘) and the chloroformyl methyl radical CH2CClO(2A‘ ‘) are formed through the isomerization of PπC. The C−C bond scission of CH2ClCO(2A‘) leads to the products CO and CH2Cl. The three-center HCl elimination from PπC, occurring via a high energy barrier (TS3) and a weakly bound hydrogen bonding (HBC1), was proposed to account for the minor yield of the HCl + HCCO observed experimentally. Multichannel RRKM−TST calculation has been carried out for the total and individual rate constants for various channels using the ab initio data. The “loose transition state” in the barrierless reaction entrance was determined by fitting the known experimental rate constant at 295 K. The kinetic calculations in this work can explain reasonably all the previous experimental results. In the temperature range 300−1500 K and the atmospheric pressure of N2, the total rate constants exhibit negative temperature dependence and can be fitted to the expression k(T) = (1.0 ± 0.2) × 10-15T -1.58±0.02 exp(−565 ± 2/T) cm3 molecule-1 s-1. Meanwhile, the rate constants show the typical fall-off behavior in the pressure range 103−108 Torr. At lower pressures (P 3 Torr), the rate constants are pressure independent and the major products are CO and CH2Cl over the whole temperature range of interest. At the high-pressure limit (P > 108 Torr), the stabilization of PπC dominates the reaction. It is found that two radical products, namely CH2ClCO(2A‘) and CH2CClO(2A‘ ‘), might be detectable in the fall-off region

Theoretical Characterizations on the Eco-Friendly Gas Tetrafluoropropyne for Electrical Insulation to Replace Sulfur Hexafluoride

Gases for electric insulation are essential for various types of high-voltage power equipment. Sulfur hexafluoride (SF6) has been a dielectric medium commonly used in electrical grids for decades but it is the most potent industrial greenhouse gas. The continuous increase of SF6 emissions in the atmosphere exerts a significant impact on global warming. The identification of suitable drop-in replacements for all SF6-filled apparatuses has been elusive experimentally and theoretically. We claim that tetrafluoropropyne, C3F4, is a breakthrough in chemical alternatives to SF6. The performance of C3F4 was assessed systematically in a 6-dimensional manner, including dielectric strength, liquefaction temperature, global warming potential, thermal stability, toxicity, and arc interruption. On the basis of the extensive ab initio calculations, it has been demonstrated rigorously that C3F4 is an environmentally sustainable solution that may fulfill the complex combination of performance, stability, safety, and environmental properties, namely, the dielectric strength is about 50% higher than that of SF6, the boiling point is −50 °C, the GWP for 100 year time horizons is only 3, the decomposition temperature is above 600 °C, the toxicity is as low as HFOs, and the interruption capability is two-thirds of SF6. Two protocols are suggested for the practical use of C3F4. First, equivalence to 0.5 MPa SF6 could be obtained by filling 0.33 MPa C3F4 pure gas and lead minimum operating temperature down to −21 °C. Second, by taking advantage of synergism effect, the 40% C3F4/60% CO2 mixture is a viable alternative to SF6 with the operating temperature −30 °C without causing any environmental and safety concerns. The present theoretical work sheds new light on the challenging topic of the development of alternative dielectric gases and may stimulate experimental tests on the electrical applications of C3F4 in the future

Computational Study of the Reaction of Atomic Oxygen with Acetone in the Gas Phase

Mechanisms and kinetics of the reaction of atomic oxygen with acetone have been investigated using ab initio quantum chemistry methods and transition state theory. The structures of the stationary points along the possible reaction pathways were obtained using the second-order Møller−Plesset theory and the coupled-cluster theory with single and double excitations with the triple-ζ quality basis sets. The energetics of the reaction pathways were calculated at the reduced second-order Gaussian-3 level and the extrapolated full coupled-cluster/complete basis set limit. The rate coefficients were calculated in the temperature range 200−3000 K, with the detailed consideration of the hindered internal rotation and the tunneling effect using Eckart and the semiclassical WKB approximations. It is shown that the predominant mechanism is the direct hydrogen abstraction producing hydroxyl and acetonyl radicals. Although the nucleophilic OC addition/elimination channel leading to CH3 and CO2 involves comparable barrier with the direct hydrogen abstraction channel, kinetically it cannot play any role in the overall reaction. It is predicted that the rate coefficients show positive temperature dependence in the range 200−3000 K and strong non-Arrhenius behavior. The tunneling effect plays a significant role. Moreover, the reaction has strong kinetic isotope effect. The calculated results are in good agreement with the available experimental data. The present rigorous theoretical work is helpful for the understanding of the characteristics of the reaction of atomic oxygen with acetone

New Mechanism for the Catalyzed Thermal Decomposition of Formic Acid^†

Mechanisms for the pyrolysis of formic acid in the gas-phase catalyzed by water dimer or formic acid itself are proposed for the first time. At the B3LYP/6-311++G(3df,3pd)//B3LYP/6-311++G(d,p) level, the barrier heights for both dehydration and decarboxylation reactions are revealed to be significantly lower than previously reported values, implying the importance of the catalytic effect of (H2O)2 and HCOOH

Theoretical Study of the Reaction of Atomic Hydrogen with Acetonitrile

The reaction of atomic hydrogen with acetonitrile has been studied using the B3LYP and Gaussian-3 (G3) methods. The geometries and vibrational frequencies of various stationary points on the potential energy surface were calculated at the B3LYP level with the 6-311G(d,p) and 6-311++G(2d,2p) basis sets. The energetics were refined at the G3 level. The G3 barrier height has been calibrated using a test set including 39 well-established reactions. It is believed that the present potential energy surface is reliable within chemical accuracy. The title reaction starts in four manners, namely direct hydrogen abstraction, C-addition, N-addition, and substitution. The corresponding barrier heights (including ZPE corrections) are 12.0, 7.6, 9.6, and 44.7 kcal/mol, respectively. The kinetics of the reaction were studied using the TST and multichannel RRKM methodologies over the temperature range 300∼3000 K, and were compared with the earlier experimental data. At lower temperatures, the C-addition step is the most feasible channel, and the major products are CH3 and HCN at lower pressures. At higher temperatures, the direct hydrogen abstraction path leading to H2 and CH2CN is apparently dominant

<i>A Priori</i> Theoretical Model for Discovery of Environmentally Sustainable Perfluorinated Compounds

Since SF₆ is the most potent greenhouse gas, the search for a viable alternative is taking on great urgency for several decades but without success. The demanding combination of performance, safety, and environmental properties for the new chemistry superior to SF₆ was thought to be nearly impossible to achieve. In contrast to the commonly used mixtures with two or three individual gases, a hybrid model has been proposed to create the new perfluorinated compounds with multiple unsaturated chemical bonds by means of full or partial integration of the parent molecules. A unique combination of a series of paradoxical properties that is high in dielectric strength and stability, low in boiling point, and significantly lower in global warming potential is achieved for the first time. The present <i>a priori</i> theoretical predictions shed new lights on the rational molecular design of the perfluorinated compounds and will greatly inspire experimental synthesis and field tests on the new chemistry for dielectric use

Decomposition and Isomerization of the CH₃CHClO Radical: ab Initio and RRKM Study

Twelve unimolecular reaction channels of the CH3CHClO radical have been studied using the ab initio G2(MP2,SVP) method. The calculations detailed three kinds of mechanisms, i.e., bond scission, intramolecular three-center elimination, and isomerization. On the basis of ab initio data, we performed multichannel (up to eight channels) RRKM calculation and numerical master equation analysis. The energy-specific rate constants, k(E), and the thermal rate constants, k(T,P), were obtained. The three-center elimination of HCl from CH3CHClO was shown to be the dominant decomposition pathway. This finding provides theoretical evidence for the previous experimental result. The implication of our results was discussed in terms of understanding the atmospheric fate of the chemically activated or thermally balanced CH3CHClO radicals

Molecular Dynamics Simulations of Ice Growth from Supercooled Water When Both Electric and Magnetic Fields Are Applied

TIP4P/2005 force-field-based classical molecular dynamics simulations were employed to investigate the microscopic mechanism for the ice growth from supercooled water when the external electric (0–10⁹ V/m) and magnetic fields (0–10 T) are applied simultaneously. Using the direct coexistence ice/water interface, the anisotropic effect of electric and magnetic fields on the basal, primary prismatic, and the secondary prismatic planes of ice Ih has been calculated. It was revealed for the first time that the solvation shells of supercooled water could be affected by the cooperative electric and magnetic fields. Meanwhile, the self-diffusion coefficient is lowered, and the shear viscosity increases considerably. The critical electric and magnetic fields to accelerate ice growth on the prismatic plane are fairly low (ca. 10⁶ V/m and 0.01 T). In contrast, the basal plane is hardly affected unless the fields increase to the order 10⁹ V/m and 10 T. Rotational dynamics of water molecules might play an important role in ice growth with the applied external fields. Density functional theory with the triple numerical all-electron basis set was used to reveal the electronic structures of the basal and primary prismatic planes of ice Ih with respect to the anisotropic effect of ice growth

Dataset of raw receiver functions and synthetic receiver functions for the robustness test

Dataset of raw receiver functions and synthetic receiver functions for the robustness test of submitted paper "Fine Shallow Structures of Binchuan Basin Inverted from Receiver Functions and Implications for Basin Evolution". The data format is "Seismic Analysis Code (SAC)"  format.   </p