International Journal of Chemical Kinetics最新文献

The kinetics of chlorine (Cl) atom reactions with a series of volatile methylsiloxanes (VMS) including hexamethyldisiloxane (L2), octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), dodecamethylpentasiloxane (L5), hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) were investigated in relative rate experiments at room temperature and atmospheric pressure. The experiments were carried out in a 0.2 m³ PFA Teflon chamber, employing proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) as the chemical-analytical tool. The following relative and absolute reaction rate coefficients were obtained using isoprene as reference compound (k_VMS/k_isoprene; k_VMS × 10¹⁰ cm³ molec⁻¹ s ⁻¹): L2 (0.32 ± 0.02; 1.31 ± 0.21), L3 (0.38 ± 0.00; 1.56 ± 0.23), L4 (0.48 ± 0.01; 1.98 ± 0.29), L5 (0.54 ± 0.03; 2.22 ± 0.34), D3 (0.14 ± 0.02; 0.56 ± 0.13), D4 (0.26 ± 0.01; 1.05 ± 0.16), D5 (0.36 ± 0.02; 1.46 ± 0.22), D6 (0.39 ± 0.02; 1.61 ± 0.25). The following relative and absolute reaction rate coefficients were obtained using toluene as reference compound (k_VMS/k_toluene; k_VMS × 10¹⁰ cm³ molec⁻¹ s ⁻¹): L2 (1.59 ± 0.18; 0.95 ± 0.14), L3 (2.25 ± 0.14; 1.35 ± 0.16), L4 (2.38 ± 0.01; 1.43 ± 0.14), L5 (3.57 ± 0.11; 2.14 ± 0.22), D3 (0.87 ± 0.01; 0.52 ± 0.05), D4 (1.48 ± 0.12; 0.89 ± 0.11), D5 (2.02 ± 0.15; 1.21 ± 0.15), D6 (2.54 ± 0.11; 1.52 ± 0.17). Our data confirm that reactions with Cl atoms need to be taken into account when assessing the decomposition of VMS in Cl-rich tropospheric environments.

Adsorption and surface ionization (SI) of morphine molecules С₁₇Н₁₉NО₃ with (m/z 285) on the surface of oxidized molybdenum was studied by voltage modulation method (VMM) with a high-vacuum mass spectrometric setup using a “black chamber” with all walls cooled with liquid nitrogen. The SI mass spectra and temperature dependences of ion current of C₉H₇N⁺CH₃ radical with m/z 144 were obtained by ionization of morphine molecules on the surface of oxidized molybdenum by using stationary SI method. They correspond to the previous results obtained by ionization of the same molecules on the surface of oxidized tungsten. The new peaks in the mass spectra can be explained by the catalytic properties of molybdenum. The sublimation heat and SI coefficient of C₉H₇NCH₃ radicals with m/z 144 was determined. The rate constants K⁺ and activation energy E⁺ for radical ions C₉H₇N⁺CH₃ with m/z 144 were determined in the adsorption of morphine molecules. For the first time the rate constants K⁰ and activation energies of thermal desorption Е° for radicals C₉H₇N⁺CH₃ with m/z 144 during adsorption of morphine molecules were determined on the surface of oxidized molybdenum with a break of (C − C₁)_β bonds with the formation of ionized radicals by SI. The dependences LnΔ(t_i) =  f(t) obtained by the VMM for all temperatures of experiments were well approximated by straight lines and made it possible, from the slope of the graphs, to calculate the average lifetimes $�{\overline{\tau }}_i$ due to the processes of dissociative SI of morphine molecules on the surface. The ionization potential of this radical was estimated. It was found that the heats of desorption weakly depend on the nature of the surface itself, therefore, in theoretical energy calculations, the Lenard-Johnson model can be used.

Corrosion inhibitors could significantly reduce the corrosion effect of seawater on carbon steels, which were widely used in seawater cooling systems and seawater desalination systems. The corrosion inhibition properties of 1,3,4-thiediazole (TD) and 2-mercapto-1,3,4-thiadiazole (MTD) and their relationship with molecular structures were systematically studied by experimental and theoretical methods. TD and MTD were composite corrosion inhibitors with the higher proportion of cathodic corrosion inhibition, and their corrosion inhibition was based on the enlarged resistance of the electrochemical dissolution reaction of the iron. Their coverage on the surface of carbon steel and the negative movement of the potential they caused would promote each other and formed the stable adsorption. The mercaptol extended the distribution range of the negative electrostatic potential of MTD, reduced the spatial steric resistance of coordination and the energy gap of the frontier molecular orbitals, and raised the number of coordination transfer electrons, which made MTD exhibited superior corrosion inhibition performance than TD. The adsorption behavior of MTD was in line with the characteristics of Langmuir adsorption and was the combination of physical adsorption and chemical adsorption. Its adsorption form was laminated adsorption, and it was conducive to the formation of feedback bonds, which led to high stability of adsorption.

Carbon steel suffers from serious corrosion in NaCl solution, the development of effective inhibitor has become a hot issue. The corrosion inhibition performance of sodium lauryl ether sulfate (AES) and lauryl betaine (BS-12) and the mixture of the two inhibitors were studied using electrochemical and weight-loss methods. Results showed the corrosion inhibition efficiency order is AES + BS-12 > BS-12 > AES, the inhibition efficiency of the inhibitor increases with the increasing of concentration and the maximum inhibition efficiency is 95.9% in the solution with 200 mg L⁻¹ AES + BS-12. Inhibitor can adsorb on Q235 surface through physical and chemical interactions and the adsorption obeys Langmuir isotherm. The migration of the corrosive ions to the metal is hindered and the metal is protected.

Based on an analytical full-dimensional potential energy surface (PES), named PES-2022, fitted to high-level ab initio calculations previously developed by our group and specifically developed to describe this polyatomic reactive process, an exhaustive kinetics analysis was performed in the temperature range 50–2000 K, that is, interstellar, atmospheric and combustion conditions. Using the competitive canonical unified theory with multidimensional tunneling corrections of small curvature, CCUS/SCT, and low- and high-pressure limit (LPL and HPL) models, in this wide temperature range we found that the overall rate constants increase with temperature at T > 300 K and T < 200 K, showing a V-shaped temperature dependence, reproducing the experimental evidence when the HPL model was used. The increase of the rate constant with temperature at low temperatures was due to the strong contribution of the tunneling factor. The title reaction evolves by two paths, H₂O + CH₂OH (R1) and H₂O + CH₃O (R2), and the branching ratio analysis showed that the R2 path was dominant at T < 200 K while the R1 path dominated at T > 300 K, with a turnover temperature of ∼260 K, in agreement with previous theoretical estimations. Three kinetics isotope effects (KIEs), ¹³CH₃OH, CH₃¹⁸OH, and CD₃OH, were theoretically studied, reproducing the experimental evidence. The kinetics analysis in the present paper together with the dynamics study previously reported showed the capacity of the PES-2022 to understand this important chemical process.

The sensitive Fluorescence Assay by Gas Expansion (FAGE) method has been used to detect methyl peroxy (CH₃O₂) and hydroperoxyl (HO₂) radicals after their conversion by titration with excess NO to methoxy (CH₃O) and hydroxyl (OH) radicals, respectively, to study the kinetics of the reaction of CH₃O₂ + HO₂ radicals. The rate coefficient of the reaction was measured in the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC) at 1000 mbar of synthetic air at T = 268–344 K, selectively detecting both radicals. Using a numerical model to fit both CH₃O₂ and HO₂ radical temporal decays globally at each temperature investigated, rate coefficients for the reaction have been obtained. The room temperature rate coefficient was found to be k_CH3O2 +HO2(295 K) = (4.6 ± 0.7) × 10⁻¹² molecule⁻¹ cm³ s⁻¹ (2σ errors) and the temperature dependence of the rate coefficient can be characterized in Arrhenius form by k_{CH3O2 + HO2}(268 K < T < 344 K) = (5.1 ± 2.1) × 10⁻¹³ × exp((637 ± 121)/T) cm³ molecule⁻¹ s⁻¹. The rate coefficients obtained here are 14%–16% lower than the literature recommended values with an uncertainty which is reduced significantly compared to previous reports.

The purpose of this paper is the investigation of the catalytic effect of graphene oxide–copper oxide nanocomposite (GCNC) on the thermal comportment and decomposition reaction kinetics of a double-base propellant (DBP) formulation. Differential scanning calorimetry (DSC) was used to conduct the thermal analysis. Using well-known iso-conversional kinetics methods, namely, Vyazovkin's nonlinear integral with compensatory effect (VYA/CE), Kissinger–Akahira–Sunose (KAS), and Flynn–Wall–Ozawa (FWO), the thermokinetic parameters for the investigated propellant, including activation energy and frequency factor, were estimated. Additionally, based on the results obtained from the kinetic analysis, the critical ignition temperature was calculated. The results showed that after the addition of GCNC, the activation energy barrier is lowered by 18%, and the critical ignition temperature is reduced.

The effect of burning rate catalyst—3% nickel salicylate (NS) with 1% carbon nanotubes (CNT)—on the combustion wave parameters of trinitroresorcinol (TNR) at 2 MPa as well as on the structure and elemental composition of the carbon frame on the surface of quenched TNR samples at 2 and 15 MPa were studied. The catalyst itself increases the burning rate by ∼4.3 times. It is shown that for the sample with NS and CNT, the accumulation of nickel particles formed during the decomposition of the catalyst occurred (∼110 times) at 2 MPa on the carbon frame. The degree of catalyst particles accumulation at 15 MPa is ∼60 times lower than at 2 MPa, so the burning rate increases by only 1.3 times. At 2 MPa the catalyst significantly (by ∼68 K) increases the combustion surface temperature, by ∼2.7 times increases the temperature gradient in the carbon frame zone, and reduces the length of the primary (fizz zone) and secondary flames. As a result, the heat release rate on the frame is 13.5 times higher than on the carbon frame of the sample without a catalyst. For TNR samples the thermal conductivity coefficient, based on the characteristics of the framework obtained, was calculated, and it was shown that the thermal conductivity coefficient of the carbon frame for a sample with NS and CNT is significantly (∼8 times) higher than for a sample without a catalyst. From the calculation of the heat balance of the c-phase at 2 MPa it follows that the combustion leading zone of the sample with a catalyst is the carbon frame, from which ∼98% of the necessary for combustion propagation heat enters the c-phase; for a sample without a catalyst, the heat gain from the gas zone is ∼20%; the leading zone is the reaction layer of the condensed phase. Thus, the mechanism of combustion catalysis of aromatic nitro compounds is the same as for double-base propellants. Two conditions are necessary for combustion catalysis: the formation of a carbon frame on the combustion surface, on which catalyst particles accumulate, and the carbon frame thermal conductivity coefficient must be significantly higher than that of the gas zone above combustion surface of the sample without a catalyst.

A number of amides, RC(O)NH₂, have been detected spectroscopically in the space between the stars. Naturally the study of how these are formed is an important question on the path of chemical evolution from the elements C, H, N, O, P, … to life because the so-called peptide-bond −C(O)−NH− is a key linkage in poly-amino acids or proteins. Both cyanides and water are abundant in the interstellar medium (ISM) and it has been suggested [J Phys Chem A. 2021;126:924-939] that these react on water–ice grains, catalyzed by acid H₃O⁺, to form firstly imidic acids R−C≡ N + H₂O → RC(OH)NH and subsequently to amides. Here we explore the kinetics in the gas-phase of the intramolecular tautomerization reaction of the imidic acids for R = H, HO, NC, H₂N, HC(O), H₃C, HOCH₂, H₂CCH,H₃C(O), H₂NCH₂, C₂H₅, and CN, particularly at low temperatures where quantum mechanical small curvature and quantized reactant states tunneling are dominant. The most reactive imidic acid is H₂NC(OH)NH which goes on to form urea, one of three known amides in the interstellar medium (ISM), which can self-react to form cytosine and uracil two canonical nucleobases in RNA. The thermochemistry ($$, $$, $$, $��\{�H_T�-�H_0�\}�$) of the imidic acids and amides is also reported as well as the tautomerization of sulfur and phosphorus analogs HC(SH)NH and HC(OH)PH.