Radical Decomposition Research Articles

Anharmonic effect of the decomposition reaction of the CF3CCl2O radical

The rate constant of the unimolecular decomposition reaction of the CF3CCl2O radical was calculated by using the method proposed by Yao and Lin (YL method). Two important channels of decomposition occurring via C–C and C–Cl bond scission were investigated. The results show that C–Cl bond scission is the dominant channel during the decomposition of the CF3CCl2O radical. Especially, the reasonable anharmonic effect on the decomposition reaction was investigated. The results show that the harmonic rate constants are higher than those of the anharmonic case in both microcanonical and canonical systems. The anharmonic effect is more evident with increasing energy.

Catalysis of radical decomposition of hydroperoxides on the surface of modified montmorillonite

4-Hydroxy-3-methyl-4′-benzeneazo(azobenzene) is used as an inhibitor to study the kinetics of radical generation upon cumyl hydroperoxide or tert-butyl hydroperoxide decomposition in microemulsions formed in the presence of cationic surfactants in organic solvents and on the surface of montmorillonite particles modified with cationic surfactants. It is demonstrated that, in contrast to microemulsions, at comparable surfactant contents, modified montmorillonite has almost no effect on the decomposition rate of hydro-peroxides. A considerable catalytic effect is only detected after Cu(2+) ions (≤0.1 wt %) are additionally applied onto the surface of its nanoparticles. The addition of polar solvents dramatically decelerates the decomposition of hydroperoxides. The activation energies of the reaction are determined for the dispersions of modified montmorillonite in toluene (56 kJ/mol) and toluene-ethanol mixture (69 kJ/mol).

Ultraviolet photodissociation dynamics of the phenyl radical

Ultraviolet (UV) photodissociation dynamics of jet-cooled phenyl radicals (C(6)H(5) and C(6)D(5)) are studied in the photolysis wavelength region of 215-268 nm using high-n Rydberg atom time-of-flight and resonance enhanced multiphoton ionization techniques. The phenyl radicals are produced from 193-nm photolysis of chlorobenzene and bromobenzene precursors. The H-atom photofragment yield spectra have a broad peak centered around 235 nm and are in good agreement with the UV absorption spectra of phenyl. The H + C(6)H(4) product translational energy distributions, P(E(T))'s, peak near ~7 kcal/mol, and the fraction of average translational energy in the total excess energy, <f(T)>, is in the range of 0.20-0.35 from 215 to 268 nm. The H-atom product angular distribution is isotropic. The dissociation rates are in the range of 10(7)-10(8) s(-1) with internal energy from 30 to 46 kcal/mol above the threshold of the lowest energy channel H + o-C(6)H(4) (ortho-benzyne), comparable with the rates from the Rice-Ramsperger-Kassel-Marcus theory. The results from the fully deuterated phenyl radical are identical. The dissociation mechanism is consistent with production of H + o-C(6)H(4), as the main channel from unimolecular decomposition of the ground electronic state phenyl radical following internal conversion of the electronically excited state.

Synthesis of free standing carbon nanosheet using electron cyclotron resonance plasma enhanced chemical vapor deposition

Carbon nanosheets (CNSs) have been synthesized by electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (PECVD) using a mixture of acetylene and argon gases on copper foil as the substrate. Micrometer-wide carbon sheets consisting of several atomic layers thick graphene sheets have been synthesized by controlled decomposition of carbon radicals in ECR-PECVD. Raman spectroscopy of these films revealed characteristics of a disordered graphitic sheet. Thick folded carbon-sheets and a semi transparent freestanding CNSs have been observed by scanning electron microscopy. This is a promising technique to synthesize free standing CNSs and can be used in the fabrication of nanoelecronic devices in future.

Reactions of o-benzyne with propargyl and benzyl radicals: potential sources of polycyclic aromatic hydrocarbons in combustion

The kinetics and mechanisms of the reactions of o-benzyne with propargyl and benzyl radicals have been investigated computationally. The possible reaction pathways have been explored by quantum chemical calculations at the M06-2X/6-311+G(3df,2p)//B3LYP/6-311G(d,p) level and the mechanisms have been investigated by the Rice-Ramsperger-Kassel-Marcus theory/master-equation calculations. It was found that the o-benzyne associates with the propargyl and benzyl radicals without pronounced barriers and the activated adducts easily isomerize to five-membered ring species. Indenyl radical and fluorene + H were predicted to be dominantly produced by the reactions of o-benzyne with propargyl and benzyl radicals, respectively, with the rate constants close to the high-pressure limits at temperatures below 2000 K. The related reactions on the two potential energy surfaces, namely, the reaction between fulvenallenyl radical and acetylene and the decomposition reactions of indenyl and α-phenylbenzyl radicals were also investigated. The high reactivity of o-benzyne toward the resonance stabilized radicals suggested a potential role of o-benzyne as a precursor of polycyclic aromatic hydrocarbons in combustion.

Dynamics of Aroma-Active Volatiles in Miso Prepared from Lizardfish Meat and Soy during Fermentation: A Comparative Analysis

The evolution of aroma-active compounds during the maturation of lizardfish meat and soybean miso was quantified and characterized using the purge-and-trap method for volatile isolation. The results revealed that miso prepared from lizardfish meat and soybeans is the result of alcoholic fermentation rather than acid fermentation. The miso prepared from soybeans matured earlier (60–90 days) than that prepared from lizardfish meat (135 days). The constancy in the volatile lipid-oxidation products, including certain aldehydes and ketones, indicated the oxidative stability of both miso products throughout the fermentation period. The present findings indicated several compounds responsible for miso aroma, including 2-methylpropanal, 3-methylbutanal, 3-methyl-1-butanol, ethyl isobutyrate, 2-methylethyl butanoate, 3-methylethyl buta-noate, ethyl decanoate, 2,3-butanedione, dimethyl trisulfide, methional, and 2-methyl butanoic acid. The formation of aldehyde can be attributed to the decomposition of hydroperoxides and peroxyl radicals, which are supposed to be initial products of oxidized fat. The volatile ketones were most likely the products of lipid and/or amino acid degradation also could possibly be produced from secondary degradation reactions involving diverse substances from the lipid during fermentation and/or may be derived from the Maillard reaction. Formation of the major volatiles in miso products were suggested as a combined effect of fungal metabolism of amino acids, sugars, and lipids, as well as the Maillard reaction during the fer-mentation period. The major difference between miso prepared from lizardfish meat and that from soybeans was the relative abundance of those odor-active compounds that finally characterize the products. Substrate specificmetabolic capacity of A. oryzae and the Maillard reaction were presumed to determine the flavor profile of the end product of miso.

Mechanism for Degradation of Nafion in PEM Fuel Cells from Quantum Mechanics Calculations

We report results of quantum mechanics (QM) mechanistic studies of Nafion membrane degradation in a polymer electrolyte membrane (PEM) fuel cell. Experiments suggest that Nafion degradation is caused by generation of trace radical species (such as OH(●), H(●)) only when in the presence of H(2), O(2), and Pt. We use density functional theory (DFT) to construct the potential energy surfaces for various plausible reactions involving intermediates that might be formed when Nafion is exposed to H(2) (or H(+)) and O(2) in the presence of the Pt catalyst. We find a barrier of 0.53 eV for OH radical formation from HOOH chemisorbed on Pt(111) and of 0.76 eV from chemisorbed OOH(ad), suggesting that OH might be present during the ORR, particularly when the fuel cell is turned on and off. Based on the QM, we propose two chemical mechanisms for OH radical attack on the Nafion polymer: (1) OH attack on the S-C bond to form H(2)SO(4) plus a carbon radical (barrier: 0.96 eV) followed by decomposition of the carbon radical to form an epoxide (barrier: 1.40 eV). (2) OH attack on H(2) crossover gas to form hydrogen radical (barrier: 0.04 eV), which subsequently attacks a C-F bond to form HF plus carbon radicals (barrier as low as 1.00 eV). This carbon radical can then decompose to form a ketone plus a carbon radical with a barrier of 0.86 eV. The products (HF, OCF(2), SCF(2)) of these proposed mechanisms have all been observed by F NMR in the fuel cell exit gases along with the decrease in pH expected from our mechanism.

ChemInform Abstract: The Importance of Developing Metal Complexes with Pronounced Catalase‐Like Activity.

AbstractReview: 56 refs.

Computational study on decomposition kinetics of CH 3 CFClO radical

The present study deals with the decomposition of haloalkoxy radical (CH3CFClO) formed from 1,1-dichloro-1-fluoroethane (HCFC-141b) in the atmosphere. The study is performed using ab-initio quantum mechanical methods. Out of the three plausible pathways of decomposition of the titled species, the one that involved the C–C bond scission and the other occurring via Cl-atom elimination have been considered for detailed study. The geometries of the reactant, products and transition states involved in the decomposition pathways are optimized and characterized at MP2 level of theory using 6-311G(d,p) basis set. Single point energy calculations have been performed at G2(MP2) level of theory. The path involving the Cl-elimination is found to be dominant and found to occur with a barrier height of 3.6 kcal mol − 1 whereas the C–C bond scission path proceeds with a barrier of 10.0 kcal mol − 1. The thermal rate constants for the above two decomposition pathways are evaluated using Canonical Transition State Theory (CTST) and these are found to be 2.9 × 108 s − 1 and 4.3 × 105 s − 1 for Cl-elimination and C–C bond scission respectively at 298 K and 1 atm. pressure. The existence of transition states on the corresponding potential energy surface is ascertained by the occurrence of only one imaginary frequency obtained during the frequency calculation. The Intrinsic Reaction Coordinate (IRC) calculation has also been performed to confirm the smooth connection of the TS to the reactant and the products. Computational studies using G2(MP2) methods have been performed to investigate the decompositions channels of CH3CFClO radical formed from HCFC-141b in the atmosphere. The results show that Cl elimination pathway is the dominant one. Rate constants of different channels considered have also been evaluated using Canonical Transition State Theory (CTST).

Adsorption and Reaction of Si2H5 on Clean and H-Covered Si(100)-(2 × 1) Surfaces: A Computational Study

A spin-polarized density functional theory calculation was carried out to characterize the adsorption and decomposition of Si2H5 radical on the clean and H-covered Si(100)-(2 × 1) surface. The adsorption structures and energies of Si2H5, Si2H4, SiH3, and SiH2 on the Si(100)-(2 × 1) surface were predicted. It was found that Si2H5, Si2H4, SiH3, and SiH2 preferentially adsorb at the dimer_a, intrarow, dimer_b, and in-dimer sites, respectively. Potential energy profiles for the reactions of Si2H5 radical on the clean and H-covered Si(100)-(2 × 1) surfaces were constructed using the nudged elastic band (NEB) method. Calculations show that the Si2H5 radical can easily decompose to Si2H4(a), SiH3(a), SiH2(a), and H(a) without any thermal activation, and the decomposition of Si(100)/Si2H5(a) → Si2H4(a)/Si(100)/H(a) may be the dominant mechanism on the clean Si(100) surface because of its low barrier and high exothermicity. The most likely mechanism for the reaction of Si2H5 on the H-covered Si(100)-(2 × 1) surfac...

Isoprene oxidation mechanisms: measurements and modelling of OH and HO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; over a South-East Asian tropical rainforest during the OP3 field campaign

Abstract. Forests are the dominant source of volatile organic compounds into the atmosphere, with isoprene being the most significant species. The oxidation chemistry of these compounds is a significant driver of local, regional and global atmospheric composition. Observations made over Borneo during the OP3 project in 2008, together with an observationally constrained box model are used to assess our understanding of this oxidation chemistry. In line with previous work in tropical forests, we find that the standard model based on MCM chemistry significantly underestimates the observed OH concentrations. Geometric mean observed to modelled ratios of OH and HO2 in airmasses impacted with isoprene are 5.32−4.43+3.68 and 1.18−0.30+0.30 respectively, with 68 % of the observations being within the specified variation. We implement a variety of mechanistic changes into the model, including epoxide formation and unimolecular decomposition of isoprene peroxy radicals, and assess their impact on the model success. We conclude that none of the current suggestions can simultaneously remove the bias from both OH and HO2 simulations and believe that detailed laboratory studies are now needed to resolve this issue.

The products of the thermal decomposition of CH3CHO

We have used a heated 2 cm × 1 mm SiC microtubular (μtubular) reactor to decompose acetaldehyde: CH(3)CHO + Δ → products. Thermal decomposition is followed at pressures of 75-150 Torr and at temperatures up to 1675 K, conditions that correspond to residence times of roughly 50-100 μs in the μtubular reactor. The acetaldehyde decomposition products are identified by two independent techniques: vacuum ultraviolet photoionization mass spectroscopy (PIMS) and infrared (IR) absorption spectroscopy after isolation in a cryogenic matrix. Besides CH(3)CHO, we have studied three isotopologues, CH(3)CDO, CD(3)CHO, and CD(3)CDO. We have identified the thermal decomposition products CH(3) (PIMS), CO (IR, PIMS), H (PIMS), H(2) (PIMS), CH(2)CO (IR, PIMS), CH(2)=CHOH (IR, PIMS), H(2)O (IR, PIMS), and HC≡CH (IR, PIMS). Plausible evidence has been found to support the idea that there are at least three different thermal decomposition pathways for CH(3)CHO; namely, radical decomposition: CH(3)CHO + Δ → CH(3) + [HCO] → CH(3) + H + CO; elimination: CH(3)CHO + Δ → H(2) + CH(2)=C=O; isomerization∕elimination: CH(3)CHO + Δ → [CH(2)=CH-OH] → HC≡CH + H(2)O. An interesting result is that both PIMS and IR spectroscopy show compelling evidence for the participation of vinylidene, CH(2)=C:, as an intermediate in the decomposition of vinyl alcohol: CH(2)=CH-OH + Δ → [CH(2)=C:] + H(2)O → HC≡CH + H(2)O.

Theoretical Study of the Equilibrium Structure, Vibrational Spectrum, and Thermochemistry of the Peroxynitrate CF2BrCFBrOONO2

The results of a theoretical study of the molecular structure and conformational mobilities of the peroxynitrate CF(2)BrCFBrOONO(2) and its radical decomposition product CF(2)BrCFBrOO are reported in this paper. The most stable structures were calculated from ab initio G3(MP2)B3 and G4(MP2) methods and from density functional theory at the B3LYP/6-311+G(d) and B3LYP/6-311+G(3df) levels of theory. The equilibrium conformation of CF(2)BrCFBrOONO(2) indicates that the bromine atoms lie in position anti to each other and possess a COON dihedral angle of 114°. A quantum statistical analysis shows that about 40% of the internal rotors can freely rotate at room temperature. Our best values for the standard enthalpies of formation of CF(2)BrCFBrOONO(2) and CF(2)BrCFBrOO at 298 K obtained from isodesmic reactions at the G3(MP2)//B3LYP/6-311+G(3df) level of theory are -144.7 and -127.0 kcal mol(-1). From these values and the enthalpy of formation of the NO(2) radical, a CF(2)BrCFBrOO-NO(2) bond dissociation enthalpy of 26.0 ± 2 kcal mol(-1) was estimated.

Thermal rate constants of the pyrolysis of n-Heptane

Rate coefficients for straight chain alkane and free radical decomposition are important in combustion process. This work reports a theoretical study of the pyrolysis of n-Heptane. The barrier heights of the C−C fission reaction, β-scission reaction and H-atom abstraction reaction, as well as geometrical parameters of the reactants, products, and transition states involved in the decomposition of n-Heptane have been calculated at the CCSD(T)/6–311G( d,p)//B3LYP/6–311G( d,p) level. The temperature-dependent rate constants for individual reaction have been obtained in the temperature range of 200–3000 K using variational transition state theory and Rice–Ramsperger–Kassel–Marcus theory. The pressure dependence rate constants have been treated by one-dimensional master equation calculations at different pressure as well as high-pressure limit. In order to facilitate the use of the reaction rate constants for chemical kinetics modeling, all of the individual rate constants were fitted to a modified three-parameter Arrhenius expression: k( T) = AT n exp(− E b / RT) at various pressures. Some of the predicted rate constants are in reasonable agreement with the available experimental and previous theoretical results. The pyrolysis mechanism and RRKM-based rate constants presented in this paper may be used in high accuracy combustion modeling.

α-Tocopherol impact on oxy-radical induced free radical decomposition of DMSO: Spin trapping EPR and theoretical studies

EPR spin trapping and theoretical methods such as density functional theory (DFT) as well as combined DFT and quadratic configuration interaction approach (DFT/QCISD) were used to identify the radicals produced in the reaction of oxy-radicals and dimethyl sulfoxide (DMSO) in the presence and absence of α-tocopherol. Additionally, the mixtures of α-tocopherol with linolenic acid and glyceryl trilinoleate as well as bioglycerols (glycerol fractions from biodiesel production) were tested. α-Tocopherol inhibited oxidation of the main decomposition product of DMSO, •CH 3 to •OCH 3 but did not prevent the transformation process of N-t-butyl- α-phenylnitrone (PBN) into 2-methyl-2-nitrosopropane (MNP). Theoretical investigations confirmed the structures of proposed spin adducts and allowed to correlate the EPR parameters observed in the experiment with the spin adducts electronic structure.

Vacuum hydride epitaxy of silicon: kinetics of monosilane pyrolysis on the growth surface

Analytical expressions relating the rate of silicon atom incorporation into a growing crystal to the typical frequency of silane molecule pyrolysis on the silicon surface in the growth temperature range are derived. Based on currently available experimental data, the range of typical decomposition frequencies of hydride molecule radicals adsorbed at the silicon wafer surface in the temperature range of 450–700°C is determined for the most widely used physicochemical models. It is shown that the most probable molecular decomposition model can be chosen based on the experimental study of the temperature dependence of the decomposition rate of adsorbed hydride molecules. A change in the silane molecule pyrolysis rate or the hydrogen desorption rate from the surface in principle makes it possible to increase the Si layer growth rate without additional substrate heating under conditions of low-temperature epitaxy (450–550°C), but no larger than by a factor of 2–3 in the former case and up to 100 times in the latter case. The analysis performed shows that physicochemical pyrolysis models in which hydrogen is trapped by the surface, mostly at the stage of decomposition of silane radicals adsorbed by the surface, are more realistic.

One-Electron Oxidation of Acetohydroxamic Acid: The Intermediacy of Nitroxyl and Peroxynitrite

The pharmacological effects of hydroxamate derivatives have been attributed not only to metal chelation or enzyme inhibition but also to their ability to serve as nitroxyl (HNO/NO(-)) and nitric oxide (NO) donors. However, the mechanism underlying the formation of these reactive nitrogen species is not clear and requires further elucidation. In the present study, one-electron oxidation of acetohydroxamic acid (aceto-HX) by (•)OH, (•)N(3), (•)NO(2), CO(3)(•-), and O(2)(•-) radicals was investigated using pulse radiolysis. It is demonstrated that only (•)OH, (•)N(3), and CO(3)(•-) radicals attack effectively and selectively the deprotonated form of the hydroxamate moiety, yielding the respective transient nitroxide radical. This nitroxide radical is a weak acid (CH(3)C(O)NHO(•), pK(a) = 9.1), which decays via a pH-dependent second-order reaction, 2k(2CH(3)C(O)NO(•-)) = (5.6 ± 0.4) × 10(7) M(-1) s(-1) (I = 0.002 M), 2k(CH(3)C(O)NO(•-) + CH(3)C(O)NHO(•)) = (8.3 ± 0.5) × 10(8) M(-1) s(-1)), and 2k(2CH(3)C(O)NHO(•)) = (8.7 ± 1.3) × 10(7) M(-1) s(-1). The second-order decomposition of the nitroxide yields transient species, one of which decomposes via a first-order reaction whose rate increases linearly upon increasing [CH(3)C(O)NHO(-)] or [OH(-)]. One-electron oxidation of aceto-HX under anoxia does not give rise to nitrite even after exposure to O(2), indicating that NO is not formed during the decomposition of the nitroxide radical. The presence of oxidants such as Tempol or O(2) during CH(3)C(O)NO(•-) decomposition had no effect on the reaction kinetics. Nevertheless, in the presence of Temopl, which does not react with NO but does with HNO, the formation of the hydroxylamine Tempol-H was observed. In the presence of O(2), about 60% of CH(3)C(O)NO(•-) yields ONOO(-), indicating that 30% NO(-) is formed in this system. It is concluded that under pulse radiolysis conditions, the transient nitroxide radicals derived from one-electron oxidation of aceto-HX decompose bimoleculary via a complex mechanism forming nitroxyl rather than NO.

Evaluation of photocatalytic production of active oxygen and decomposition of phenol in ZnO suspensions

Photocatalytic production of hydroxyl radical (·OH) and superoxide anion (·O2 −) and decomposition of phenol in ZnO suspensions were studied in the present paper. Nano-sized ZnO (n-ZnO) produced by chemical precipitation method with particle size of ca. 50 nm and commercial ZnO (c-ZnO) produced by indirect method (oxidation of the metal in oxygen) with particle size of ca. 500 nm were used in this work. The photocatalytic production of ·OH and superoxide anion ·O2 − in the suspensions of ZnO were measured by electron paramagnetic resonance (EPR) spectrometer, and the results indicate that the c-ZnO generated more ·OH and ·O2 − than the n-ZnO. The photocatalytic activity of ZnO was evaluated by the decomposition of phenol in the suspensions, and the results show that the c-ZnO has stronger activity than the n-ZnO, which is in accordance with the results of the production of active oxygen. These results reveal that the particles size is not the main factor that influences the photocatalytic activity of ZnO. The preparation method, which can affect the characteristics of surfaces and the defects inside the ZnO, may have some effect on the photocatalytic activity.

Kinetic and Mechanistic Study of the Reactions of Atomic Chlorine with CH3CH2Br, CH3CH2CH2Br, and CH2BrCH2Br

A laser flash photolysis-resonance fluorescence technique has been employed to investigate the reactions of atomic chlorine with three alkyl bromides (R-Br) that have been identified as short-lived atmospheric constituents with significant ozone depletion potentials (ODPs). Kinetic data are obtained through time-resolved observation of the appearance of atomic bromine that is formed by rapid unimolecular decomposition of radicals generated via abstraction of a β-hydrogen atom. The following Arrhenius expressions are excellent representations of the temperature dependence of rate coefficients measured for the reactions Cl + CH(3)CH(2)Br (eq 1 ) and Cl + CH(3)CH(2)CH(2)Br (eq 2 ) over the temperature range 221-436 K (units are 10(-11) cm(3) molecule(-1) s(-1)): k(1)(T) = 3.73 exp(-378/T) and k(2)(T) = 5.14 exp(+21/T). The accuracy (2σ) of rate coefficients obtained from the above expressions is estimated to be ±15% for k(2)(T) and +15/-25% for k(1)(T) independent of T. For the relatively slow reaction Cl + CH(2)BrCH(2)Br (eq 3 ), a nonlinear ln k(3) vs 1/T dependence is observed and contributions to observed kinetics from impurity reactions cannot be ruled out; the following modified Arrhenius expression represents the temperature dependence (244-569 K) of upper-limit rate coefficients that are consistent with the data: k(3)(T) ≤ 3.2 × 10(-17)T(2) exp(-184/T) cm(3) molecule(-1) s(-1). Comparison of Br fluorescence signal strengths obtained when Cl removal is dominated by reaction with R-Br with those obtained when Cl removal is dominated by reaction with Br(2) (unit yield calibration) allows branching ratios for β-hydrogen abstraction (k(ia)/k(i), i = 1,2) to be evaluated. The following Arrhenius-type expressions are excellent representations of the observed temperature dependences: k(1a)/k(1) = 0.85 exp(-230/T) and k(2a)/k(2) = 0.40 exp(+181/T). The accuracy (2σ) of branching ratios obtained from the above expressions is estimated to be ±35% for reaction 1 and ±25% for reaction 2 independent of T. It appears likely that reactions 1 and 2 play a significant role in limiting the tropospheric lifetime and, therefore, the ODP of CH(3)CH(2)Br and CH(3)CH(2)CH(2)Br, respectively.

The special features of adsorption and the kinetics of decomposition of monosilane molecules on the epitaxial surface of silicon

Analytic equations relating the rate of the incorporation of silicon atoms into a growing crystal to the characteristic frequency of the pyrolysis of silane molecules on the surface of silicon were obtained over the temperature range corresponding to the epitaxial growth of silicon films. As distinct from the earlier works, it was assumed that adsorbed silicon atoms and monosilane molecules formed double bonds with the surface. The data of technological experiments for the most extensively used pyrolysis models obtained thus far were used to determine the region of the characteristic frequencies of the decomposition of hydride molecule radicals adsorbed on the surface of a silicon plate over the temperature range 450–700°C. The temperature dependence of the frequency of monosilane molecule decomposition was shown to be to a great extent determined by the form of the temperature dependence of the \( \tilde v_{SiH_2 }^0 \) preexponential factor. It was also found that the characteristic frequency of the decomposition of silane molecules was sensitive to the stage of pyrolysis at which hydrogen atoms released from silane molecules were captured by the surface. Decomposition occurred at the highest rate if hydrogen molecules were adsorbed at the stage of the adsorption of monosilane. The lowest rate of decomposition was observed if hydrogen molecules were adsorbed at the stage of the decomposition of radicals already captured by the surface. The temperature dependence of the coefficient of adsorption of monosilane molecules was characterized by a negative activation energy of the process for almost all the most important system models over the temperature range of growth. At elevated growth temperatures, the adsorption of monosilane molecules by the surface of silicon proceeded via an intermediate state characterized by the difference of desorption and chemisorption energies on the order of 0.28 eV.