G2 Methods Research Articles

Formation pathways of polycyclic aromatic hydrocarbons (PAHs) in butane or butadiene flames.

The reaction pathways from phenyl radicals to phenanthrene (A3) and pyrene (A4) via C2H3 and C4H4 additions were investigated using the G3(MP2, CC) method. Rate constants of elementary reactions were calculated. The influence of additions, H-abstraction ways and reactive sites on the reaction rates were considered. These polycyclic aromatic hydrocarbon (PAH) formation pathways were used to improve the combustion chemistry model for C4 fuels, and the results from the improved model and the original model were compared with experimental data. H atoms are important for PAH formation owing to their influential roles in the production of aromatic radicals and stable aromatic structures. C2H3 and C4H4 addition reactions can occur at low temperature, and need less energy than C2H2 addition. The PAH formation pathways determined from G3 calculations, which were used to improve the model, were effective in promoting PAH formations in this model. Comparison of PAH formation in butane and butadiene flames showed both the C2H3 and C4H4 addition pathways included in this work can improve the formation of PAHs in butadiene and butane flames. C4H4 addition pathways in a butane flame were better for PAH formation than C2H3 addition.

The Evaluation of Smart City Construction Readiness in China Using CRITIC-G1 Method and the Bonferroni Operator

With the development of information science and technology such as big data and cloud computing, the proposal of smart city realizes the transformation of urban governance from growth mode to refine operation mode. Smart city is an advanced stage of urban informatization development and urban governance, which must have a certain development foundation and corresponding environmental protection, that is, the preparation for smart city construction. First of all, through literature research and expert interviews, the critical success factors influencing the construction of smart city are selected, and the evaluation index system of smart city construction readiness is established; Secondly, the objective and subjective weights of indicators are determined and combined by using CRITIC and G1 methods to design. Thirdly, the Bonferroni operator is used to build the evaluation model of smart city construction readiness, calculate and sort the final evaluation value of the scheme; Finally, taking 30 cities in the list of national smart cities as the object of empirical research, the results show that the evaluation model constructed by the text can fully consider the contrast strength and conflict between indicators, eliminate the interaction between indicators, make the evaluation more objective and reasonable, and provide decision-making reference for measuring the construction readiness of smart cities.

From Very Strong to Inexistent Be-Be Bonds in the Interactions of Be2 with π-Systems.

Isolated Be2 is a typical example of a weakly bound system, but interaction with other systems may give rise to surprising bonding features. The interactions between Be2 and a set of selected neutral Cn Hn (n=2-8) π-systems have been analyzed through the use of G4 and G4MP2 ab initio methods, along with multireference CASPT2//CASPT2 calculations. Our results systematically show that the Cn Hn -Be2 -Cn Hn clusters formed are always very stable. However, the nature of this interaction is completely different when the π-system involved is a closed shell species (n=2, 4, 6, 8), or a radical (n=3, 5, 7). In the first case, the interaction does not occur with the π-system as a whole, but with specific C centers yielding rather polar but strong C-Be bonds. Nonetheless, although the Be-Be distances in these complexes are similar to the ones in compounds with ultra-strong Be-Be bonds, a close examination of their electron density distribution reveals that no Be-Be bonds exist. The situation is totally different when the interaction involves two π-radicals, Cn Hn -Be2 -Cn Hn (n=3, 5, 7). In these cases, a strong Be-Be bond is formed. Indeed, even though Be is electron deficient, the Be2 moiety behaves as an efficient electron donor towards the two π-radicals, so that the different Cn Hn -Be2 -Cn Hn (n=3, 5, 7) clusters are the result of the interaction between Be2 2+ and two L- anions. The characteristics of these two scenarios do not change when dealing with bicyclic π-compounds, such as naphthalene and pentalene, because the interaction with the Be2 moiety is localized on one of the unsaturated cycles, the other being almost a spectator.

Study on structural growth behavior and simulated photoelectron spectroscopy of Sc2Sin(0,−1) (n ≤ 8) clusters using G4(MP2) theory

The lowest energy structures and of Sc2Sin (n ≤ 8) and their anions were probed with the high level of G4(MP2) methods. The most stable structures of Sc2Sin(0,−1) clusters were predicted to belong to the substitutional types in this work. The simulated PES of the negatively charged ions, especially for Sc2Si5−, had good correspondence with the experimental spectrogram. The little differences between the calculated and experimental AEAs and VDEs may indicate that the most stable structures for Sc2Sin clusters reported were reliable. Analysis of dissociation energies revealed that the species of Sc2Sin possessed higher stability than ScSin clusters. The Sc atoms acted as electron donors for neutral and anionic Sc2Sin (n = 1–5); however, silicon clusters act as electron donors for anionic Sc2Si6− and Sc2Si7−. The investigation of charge transfer has shown that the dipole moments were all been weakened when the neutral Sc2Sin clusters received an additional electron with the exception of Sc2Si3− and Sc2Si8−. The dipole moments were 0 D for neutral Sc2Si3, Sc2Si8 and anionic Sc2Si4−, which in turn caused the nonpolar result.

Integration of modern computational chemistry and ASPEN PLUS for chemical process design

AbstractThermodynamic properties and fluid phase equilibria are crucial for the design and development of a chemical process. However, such data may not always be available, particularly for fine or specialty chemicals. In this work, we evaluate the reliability of using modern computational chemistry combined with recently developed predictive thermodynamic models to provide all the thermodynamic properties required in process design with ASPEN PLUS. Specifically, the G3 method is used for the ideal gas heat capacities and properties of formation, and the PR+COSMOSAC equation of state and COSMO‐SAC activity coefficient model are utilized for the properties and phase behaviors of pure and mixture fluids. These methods are chosen because they do not require any species‐dependent parameters and can, in principle, be applied to any chemical species. For a set of 972 chemicals, it is found that most properties can be predicted with a satisfactory accuracy (less than 10%: critical temperature [5%], critical pressure [10%], critical volume [5%], constant pressure ideal gas heat capacity [5%], and heat of vaporization [10%], except for the acentric factor [33%] and vapor pressure [73%]). Furthermore, the predicted results show little bias suggesting that these theoretically based methods are reliable for new chemicals for which experimental data are not yet available. Our analyses show that better accuracy in the prediction of vapor pressure and formation enthalpy and free energy is necessary for the design of chemical processes without relying on any experimental input. Nonetheless, these methods often provide reliable relative property values (e.g., relative value of normal boiling temperature can be predicted with 94% accuracy), making it possible to screen for new chemicals for improving existing processes.

Novel Equine Faecal Egg Diagnostics: Validation of the FECPAKG2.

Faecal egg counts (FECs) are the standard method of diagnosing the level of parasitic helminth egg shedding in horses and other grazing animals. Testing before treatment is an important factor in slowing the appearance of anthelmintic resistance in nematode parasites. The FECPAKG2, optimised for livestock, is reported to allow owners to perform FECs on their own animals without the need for a separate microscope or any specialist knowledge by tapping into remote expertise. However, the performance of the FECPAKG2 has yet to be assessed for equids. Therefore, a comparison of the FECPAKG2 (G2) method with an accepted equine FEC method (FECPAKG1(G1)) was performed, using faecal samples from 57 horses in Wales and 22 horses in New Zealand. There was a significant correlation between the FECs obtained by the two methods (p < 0.001) and no effect of the country of origin on the data (p = 0.157). The mean percentage accuracy compared to the control values (mean G2 count as a percentage of the mean G1 count, ±SStandard Error (SE)) was 101 ± 4%. There was no significant interaction between the method applied and the country of origin of the data (p = 0.814). The relative accuracy of the G2 method compared to the control method (FECPAKG1) was not affected by the level of infection (p = 0.124) and it was concluded that the FECPAKG2 method is a suitable method of performing FECs in horses. It is anticipated that the user-friendliness of the method will increase the uptake of FECs amongst horse owners, either by the direct use of the technology or through their veterinary practice, likely slowing the development of anthelmintic resistance.

Thermodynamic properties of 1,3,3-trimethylcyclopropene

The energy of combustion of liquid 1,3,3-trimethylcyclopropene was obtained in isoperibolic calorimeter at T = 298.15 K. The saturated vapour pressures were determined by the comparative ebulliometry in the temperature range 295–310 K. The normal boiling temperature and the enthalpy of vaporization were estimated based on p-T-data. The enthalpy of vaporization was measurement by calorimetric method at T = 298.15 K. The density was determined by pycnometric method at T = 293.15 K. The formation enthalpies of the compound in liquid and gas states were determined using the obtained experimental data. The enthalpies of formation in the gaseous state for cyclopropene and its methyl-substituted derivatives were estimated by G4 method.

Gas-to-Liquid Phase Transition of PAH at Flame Temperatures.

Significant evidence has shown that soot can be formed from polycyclic aromatic hydrocarbon (PAH) in combustion environments, but the transition of high molecular PAH from the gas phase to soot in a liquid or solid state remains unclear. In this study, the relationships between the boiling points of various planar PAHs and their thermodynamic properties are systematically investigated, to find a satisfactory marker for the phase transition event. Temperature-dependent thermodynamic properties, including entropy, specific heat capacity, enthalpy, and Gibbs free energy, are simultaneously calculated for PAHs, using density functional theory and three composite compound methods. Comparison of the results indicates that the individual G3 method, plus an atomization reaction approach, produces the most accurate thermochemistry parameters. Compared to entropy, enthalpy, and Gibbs free energy, the specific heat capacity at 298 K is found to be a better marker for the boiling point of PAHs due to the observed linear correlation, predictable characteristics, and fidelity of accuracy as a function of temperature. The correlation equation Y = 10.996X + 122.111 is proposed (where Y is the boiling temperature (K) and X is Cp at 298 K (cal/K/mol)). The standard deviation is as low as 16.7 K when comparing the calculated boiling points and experimentally determined values for 25 different aromatic species ranging from benzene to ovalene (C32H14). The effects of carbon number, structural arrangement, and partial pressure on the boiling point of large planar PAH are discussed. The results reveal that the carbon number in large planar PAH is the dominant factor determining its boiling points. It is shown that PAHs containing about 60-65 carbon atoms are likely to exist as liquids in flames, although the partial pressure of such species is very low.

Theoretical O–CH3 bond dissociation enthalpies of selected aromatic and non-aromatic molecules

Although methyl transfer reactions are important in both chemical and biological systems, there is a need for thermodynamic parameters related to methyl affinity and O–CH3 bond dissociation enthalpies (BDEs) relevant to a full understanding of the mechanisms of methyl transfer reactions. As a prelude to the construction of a database of O–CH3 BDEs, the present work examines the reliability of a series of theoretical methods for the prediction of O–CH3 BDEs using a set of 25 compounds that included both aromatic and non-aromatic molecules. The BDEs calculated by density functional theory (DFT) with traditional exchange–correlation functions exhibited much larger errors than those obtained by either the M06-2X or G4 methods. For the non-aromatic compounds, M06-2X/def2-TZVP performed slightly better than G4, but G4 was more accurate for the aromatic molecules. As a result, we recommend G4 as the preferred method for the theoretical estimation of O–CH3 bond dissociation enthalpies, although M06-2X may be a good alternative for large complex molecules when the use of G4 is impractical.

Rate rules for hydrogen abstraction reaction kinetics of alkenes from allylic sites by HO2 radical

Hydrogen abstraction reaction from allylic sites by HO2 radical is important in the ignition chemistry of alkenes. A systematic study with a series of C4-C7 alkenes as reactants is performed in present work to obtain the rate rules for the reaction class using G4 method coupled with transition state theory. The size and chain length of substituent groups and the configuration of reactant have little effect on the rate constants within a class. Hence, the rate rules are concluded by taking the average of the rate constants of a representative set of reactions. The reactivity for both alkenes and alkanes are similar with tertiary hydrogen possessing the highest activity and primary hydrogen possessing the lowest activity. The rate constants of alkanes and alkenes for these reaction classes are quite different at low temperatures. The obtained rate rules are applicable to the similar reaction classes of larger alkenes and alkanes.

Structure-property relationships in substituted diphenyl ethers: Non-nearest interactions of methyl-, methoxy-, hydroxyl-, amino-, and nitro-substituents

The standard molar enthalpies of formation, ΔfHmo(liq/cr) of diphenyl ether substituted with nitro substituents were measured by the high-precision combustion calorimetry. Enthalpies of vaporisation/sublimation Δl,crgHmo(298.15 K) of these compounds were obtained by the transpiration method. Enthalpies of fusion were measured by DSC. Gas-phase enthalpies of formation ΔfHmo(g, 298.15 K) of substituted diphenyl ethers calculated by the G4 method were in an excellent agreement with the experimental results. A set of thermodynamic properties of diphenyl ether derivatives of benchmark quality was recommended for thermochemical calculations and for quantification of non-nearest interactions of methyl-, methoxy-, hydroxyl-, amino- and nitro-substituents on the diphenyl ether aromatic system.

Thermochemistry of di-substituted benzenes: nitro- and dimethylamino benzaldehydes

Standard molar enthalpies of vaporization/sublimation of nitro and amino-substituted benzaldehydes were obtained from the temperature dependence of vapour pressure measured by the transpiration method. Enthalpies of fusion of these compounds were measured by using DSC. Solution enthalpies of nitro and amino-substituted benzaldehydes were measured by using a solution calorimeter. Available from literature primary experimental results on temperature dependences of vapour pressures have been collected and they have been treated uniformly in order to derive vaporization/sublimation enthalpies at the reference temperature 298.15 K. Standard molar enthalpies of formation of crystalline isomers of nitro-benzaldehydes were measured by using combustion calorimetry. Gas phase molar enthalpies of formation of substituted benzaldehydes were calculated by the high-level quantum-chemical G4 method and they were used for evaluation of available experimental results. A set of thermodynamic properties of substituted benzaldehydes was recommended as reliable reference properties for thermochemical calculations. Simple group-additivity procedures were developed for estimation of vaporization enthalpies, gas-phase, and liquid-phase enthalpies of formation of substituted benzenes.

Liquid organic hydrogen carriers: Hydrogen storage by di-phenyl ether derivatives: An experimental and theoretical study

The liquid organic hydrogen carriers (LOHCs) are promising materials for hydrogen storage. The standard molar enthalpies of formation, ΔfHmo (liq/cr) of diphenyl ether substituted with amino substituents were measured by the high-precision combustion calorimetry. Enthalpies of vaporisation/sublimation Δl,crgHmo (298.15 K) of these compounds were obtained by the transpiration method. Enthalpies of fusion were measured by DSC. Gas-phase enthalpies of formation ΔfHmo (g, 298.15 K) of substituted diphenyl ethers calculated by the G4 method were in an excellent agreement with the experimental results. Enthalpies of the hydrogenation/dehydrogenation reactions of diphenyl ether derivatives were estimated and compared with the data available for other potential LOHC. A set of thermodynamic properties of diphenyl ether derivatives of benchmark quality was recommended for thermochemical calculations. Equilibrium temperatures of hydrogenation/dehydrogenation processes were calculated and compared with those of benzene derivatives. Due to the high hydrogen storage capacity, as well as very low volatility, these compounds could be considered as seminal candidates for LOHC.

DFT and ab initio calculations of ionization potentials, proton affinities and bond dissociation enthalpies of aromatic compounds

Abstract Theoretical study of phenol, thiophenol, benzeneselenol, aniline and their para-amino and paranitro derivatives is presented. Neutral molecules, their deprotonated forms, neutral radicals, and radical cations were studied using three Density Functional Theory (DFT) functionals as well as combined DFT and ab initio G4 method in order to calculate the N—H, O—H, S—H, and Se—H bond dissociation enthalpies (BDE), proton affinities of corresponding anions (PA) and ionization potentials (IP) of studied compounds. These quantities represent fundamental reaction enthalpies related to the radical scavenging action of primary antioxidants. Calculated values were compared with available experimental data to assess applicability of the computational approaches employed. M06-2X/6-311++G(d,p) and G4 methods showed the best agreement with the available experimental gas-phase reaction enthalpies.

Computational study on thermodynamic properties of Fischer-Tropsch synthesis process

Using the highly accurate G4 method, we computed the thermodynamic data of 1287 possible reaction products under a wide range of reaction conditions in the Fischer-Tropcsh synthesis (FTS) process. These accurate thermodynamic data provide basic thermodynamic quantities for the actual chemical engineering process and are useful in analyzing product distribution because FTS demonstrates many features of an equilibrium-controlled system. Our results show that the number of thermodynamically allowed products to increase when lowering temperature, raising pressure, and raising H2/CO ratio. At low temperature, high pressure and high H2/CO ratio, many products are thermodynamically allowed and the selectivity of product has to be controlled by kinetic factors. On the other hand, high selectivity of lighter products can be realized in thermodynamics by raising temperature and lowering pressure. We found that the equilibrium product yield will reach a maximum and remain unchanged when lowering temperature, raising pressure, and raising H2/CO ratio to some limits, implying that optimizing reaction conditions has no effect on equilibrium product yields beyond these limits. The thermodynamic analysis is also useful in designing and evaluating FTS reaction mechanisms. We found that reaction pathways through formaldehyde should be discarded because of its extremely low equilibrium yield. Recently, in the FTS process using metal-oxide-zeolite catalysts for the highly selective production of C2—C4 olefins and aromatic hydrocarbons, there are several guesses on the possible reaction intermediates entering the zeolite channel. Our results show that ketene, methanol, and dimethyl ether are three possible reaction intermediates.

Diphenyl Ether Derivatives as Potential Liquid Organic Hydrogen Carriers: Thermochemical and Computational Study

The liquid organic hydrogen carriers (LOHCs) are promising materials for hydrogen storage. The standard molar enthalpies of formation, ΔfHmo(liq/cr) of diphenyl ether substituted with methyl, methoxy, and hydroxyl substituents were measured by the high-precision combustion calorimetry. Enthalpies of vaporization/sublimation Δl,crgHmo(298.15 K) of these compounds were obtained by the transpiration method. Enthalpies of fusion of 2- and 4-hydroxy-diphenyl ether were measured by differential scanning calorimeter. Gas-phase enthalpies of formation ΔfHmo(g, 298.15 K) of substituted diphenyl ethers calculated by the G4 method were in an excellent agreement with the experimental results. Enthalpies of the hydrogenation/dehydrogenation reactions of diphenyl ether derivatives were estimated and compared with the data available for other potential LOHC. A set of thermodynamic properties of diphenyl ether derivatives of benchmark quality was recommended for thermochemical calculations. Equilibrium temperatures of hy...

Effects of Two CO2 Stunning Methods on the Efficacy of Stunning and Blood Stress Indicators of Turkeys under Commercial Processing Conditions

ABSTRACTThe effect of CO2 gas-stunning methods (G1: 30% CO2 15 sec, 55% CO2 40 sec, 70% CO2 45 sec; G2: 30% CO2 15 sec, 80% CO2 85 sec) on the efficacy of stunning, blood stress indicators and meat quality of turkeys were assessed. A total of 375 turkeys (125 heavy males, 125 light males, and 125 light females) were used. After stunning, clinical parameters (posture-loss, wing-flapping, breathing, response to toe-pinching, eye movements, and palpebral, corneal and pupillary reflexes) and glucose, lactate and cortisol levels were assessed. The G2 method showed a higher percentage of correctly stunned birds (81.3 vs. 70.7%) and lower cortisol levels (0.44 vs. 1.22 g/dL). The weight and sex had a significant influence on the behavioral and physiological responses after stunning. The G2 method was found to be acceptable for animal welfare during stunning, based on both the percentage of animals correctly stunned and dead (92% to 100%) and the blood cortisol level after stunning.

ANALISIS METODE CHEATING PADA TES BERSKALA BESAR

This study aimed to reveal: (1) the characteristics of items of Chemistry Test in National Examination by using the classical test theory and item response theory; (2) the amount of cheating which occured by using Angoff's B-index Method, Pair 1 Method, Pair 2 Method, Modified Error Similarity Analysis (MESA) Method, and G2 Method; (3) the methods that detect more cheating in the implementation of the Chemistry Test in National Examination for high schools in the year 2011/2012 in Maluku Province. The results of the analysis with the classical test theory approach show that 77.5% items have item difficulty functioning well, 55% items have discrimination yet qualified and 70% items have distractor that works well with the index reliability test of 0,772. The analysis using the item response theory approach shows that 14 (35%) items fit with the model, the maximum function information is 11,4069 at θ = -1,6, and the magnitude of the error of measurement is 2,296. The number of pairs who are suspected of cheating is as follows: 13 pairs according to Angoff's B-index Method, 212 pairs according to Pair 1 Method, 444 pairs according to Pair 2 Method, 7 pairs according to MESA Method, and 102 pairs according to G2 Method. The most widely detecting cheating in a row is a Pair 2, Pair 1, G2, Angoff's B-index, and MESA.

Theoretical studies of $${{\mathrm{{CN} + {H}}_{2}({\mathrm{D}}_{2})}}$$ reactions: competition between H(D)-abstractions in $${\mathrm{H(D) + HCN(DCN)/HNC(DNC)}} $$ channels

The $$\hbox {CN} + \hbox {H}_{2}$$ reaction was investigated by considering the two possible channels, $$\hbox {H} + \hbox {HCN}$$ and $$\hbox {H} + \hbox {HNC}$$ , taking into account the isotopic effects and with the vibrationally excited states. The frequencies and structures for all species of the $$\hbox {CN} + \hbox {H}_{2}/\hbox {D}_{2}$$ reaction were calculated using G3 method for further kinetics calculation. The thermal rate constants were calculated using the conventional transition-state theory (TST) and canonical variational transition-state theory (CVT) by APUAMA code, over the temperature range from 200 to 4000 K. In addition, rate coefficients for vibrationally excited reactants CN (v = 1) or $$\hbox {H}_{2}$$ (v = 1) or $$\hbox {D}_{2}$$ (v = 1) are presented. The branching ratio for the partitioning into H/D + HCN/DCN or H/D + HNC/DNC has, also, been determined. The results showed that the $$\hbox {CN} (v=0) + \hbox {H}_{2} (v=0) \rightarrow \hbox {H} + \hbox {HCN} $$ channel is dominant at all range of temperature, while $$\hbox {CN } (v=1) + \hbox {H}_{2} (v=0) \rightarrow \hbox {H} + \hbox {HNC}$$ channel is dominant at T $$\ge $$ 1900 K. The isotopic effects are the same behavior that $$\hbox {CN}(v=0,1) + \hbox {H}_{2}(v=0,1) \rightarrow \hbox {H} + \hbox {HCN/HNC}$$ reactions. Reasonable agreement was found between the experimental results and the rate constants predicted by conventional transition-state theory, with tunneling correction, using the theoretical transition-state properties.

Concentrations of water and thionyl chloride complexes and clusters: hydrolysis products in the gas phase

The presence of water complexes and clusters in hydrolysis and hydration reactions implies complex multi-step processes involving various mechanisms. The concentration of neutral and charged complexes and clusters in the reaction mixture affects the rate and mechanism of hydrolysis. Therefore, the aim of this work was to calculate the concentrations of the complexes and clusters involved in gas -phase hydrolysis of thionyl chloride, as well as to establish the most probable reaction channels. Based on the thermodynamic data obtained by the B3LYP/6–311++G(2d,2p), MP2/aug-cc-pVTZ and G4 methods of quantum chemical modelling, the gas-phase concentrations of the complexes and clusters of water and thionyl chloride, as well as the hydrolysis products of the latter, were calculated. The structures of water complexes of composition (H 2 O) n (n = 1-5.8) were identified and optimised. Acyclic structures of the (H2O)4 and (H2O)5 complexes were identified in the gas phase having concentrations different from those calculated in cyclic complexes. Calculated concentrations of charged complexes and clusters (H+ )∙(H 2 O) n and (H 2 O) n ·(OH - ) Cl - (H 2 O) n , SOCl + (H 2 O) n , (SOCl 2 (H 2 O) n ) - are negligible. Therefore, the assumption concerning the hydrolysis of formed or existing ionic particles in the gas phase inside water clusters can be excluded. Concentrations of SOCl 2 (H 2 O) n and HCl (H 2 O) n neutral clusters range from 1014 to 101 molecules/cm3 , depending on the number of water molecules in a cluster. SOCl 2 (H 2 O) and HCl(H 2 O) are characterised by the highest concentration. A calculation of SOCl 2 (H 2 O) n cluster concentrations was performed under the assumption that the concentration of thionyl chloride is equal to the concentration of saturated water vapour, which is quite possible near industrial facilities for the production of high-capacity current sources. The most probable channels for hydrolysis are presented by reactions of complexes and clusters having the highest concentrations. These reactions of (H 2 O) n and SOCl 2 (H 2 O) n neutral clusters are in a good agreement with the results of previous work.