In situ quadrupole mass spectrometry study of atomic-layer deposition of ZrO2 using Cp2Zr(CH3)2 and water

Reactions during the atomic layer deposition (ALD) process of ZrO(2) from Cp(2)Zr(CH(3))(2) and deuterated water as precursors were studied with a quadrupole mass spectrometer (QMS) at 210-440 degrees C. The detected reaction byproducts were CpD (m/z = 67) and CH(3)D (m/z = 17). Almost all (90%) of the CH(3) ligands were released during the Cp(2)Zr(CH(3))(2) precursor pulse because of exchange reactions with the OD-terminated surface, and the rest, during the D(2)O pulse. About 40% of the CpD was released during the metal precursor pulse, and 60%, during the D(2)O pulse. ALD-type self-limiting growth was confirmed from 210 to 400 degrees C. However, below 300 degrees C the growth rate was low. Precursor decomposition affected the film growth mechanism at temperatures exceeding 400 degrees C.     

Role of water in the atomic layer deposition of TiO(2) on SiO(2)

Atomic layer deposition (ALD) of TiO(2) on SiO(2) powder using sequential addition of TiCl(4) and H(2)O vapors has been investigated by infrared spectroscopy. In the first cycle, TiCl(4) reacts monofunctionally or bifunctionally with surface silanols forming (Si-O-)(n)Ti-Cl(4)(-)(n) (n = 1, 2) species. Subsequent addition of water vapor leads to the hydrolysis of the (Si-O-)(n)Ti-Cl(4)(-)(n) to form a Ti-O-Ti network, and at the same time, some cleavage of Si-O-Ti bonds occurs, regenerating Si-OH in the process. It is shown that the species formed on the surface in the first TiCl(4) dose are temperature dependent. However, after addition of H(2)O vapor, the amount of TiO(2) deposited in the first complete cycle is independent of reaction temperature. In the second and above cycles, the amount of TiO(2) deposited as a function of ALD cycles strongly correlates with the amount of water on the surface. This, in turn, led to a temperature dependence of the growth rate of the TiO(2) per cycle.     

DFT investigation of the mechanism of CH2CO + O(3P) reaction

A detailed theoretical survey of the potential energy surface (PES) for the CH₂CO + O(³P) reaction is carried out at the QCISD(T)/6‐311+G(3df,2p)//B3LYP/6‐311+G(d,p) level. The geometries, vibrational frequencies, and energies of all stationary points involved in the reaction are calculated at the B3LYP/6‐311+G(d,p) level. More accurate energy information is provided by single‐point calculations at the QCISD(T)/6‐311+G(3df,2p) level. Relationships of the reactants, transition states, intermediates, and products are confirmed by the intrinsic reaction coordinate (IRC) calculations. The results suggest that P1(CH₂+CO₂) is the most important product. This study presents highlights of the mechanism of the title reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Adsorption reactions of dimethylaluminum isopropoxide and water on the H/Si(100)-2 x 1 surface: initial reactions for atomic layer deposition of Al2O3

The surface reaction pathways of dimethylaluminum isopropoxide (DMAI) and water with the H/Si(100)-2 x 1 surface were theoretically investigated with SIMOMM:MP2/6-31G(d). The oxygen atom in DMAI stabilizes an initial complex, facilitating the approach of DMAI to the surface. The methane loss reaction, propane loss reaction, methylation, hydrogen loss reaction, and ring closing reaction channels of the DMAI-surface reactions were identified. Among these, the methane loss reaction depositing -Al(CH3)OCH(CH3)2 was found to be the major channel due to low barrier height and large exothermicity. The ring closing reaction is kinetically the second most accessible channel, even though it is not thermodynamically favorable. On the basis of these theoretical results, recent experimental data were reinterpreted such that the experimentally observed peaks of CH4 and CH(CH3)2OH are in fact the products of these two channels. The propane loss reaction is kinetically the third most probable channel. It produces the surface Si-O bond, which is a reaction unique to DMAI as compared to trimethylaluminum. In summary, the oxygen substitution not only affects the basic nature of the existing potential energy surfaces but also opens new possibilities.     

In situ FT-IR studies on the mechanism of selective catalytic reduction of NOx by propene over SnO2/Al2O3 catalyst

The mechanism of the selective catalytic reduction (SCR) of NOx by propene over SnO2/Al2O3 catalyst in the presence of oxygen has been investigated using in situ Fourier transform infrared (FT-IR) spectroscopy. In situ IR measurements indicate that acetate and formate, which are the derivatives of the partial oxidation of propene, play a crucial role in the formation of NCO by reacting with the reactive monodentate nitrate species. The resulting NCO species subsequently reacts with NOx to form N2. The presence of oxygen substantially contributes to the partial oxidation of propene and thus shows a promoting effect for the NOx reduction.     

UV absorption spectra of HO2, CH3O2, C2H5O2, and CH3C(O)CH2O2 radicals and mechanism of the reactions of F and Cl atoms with CH3C(O)CH3

Pulse radiolysis techniques were used to measure the gas phase UV absorption spectra of the title peroxy radicals over the range 215–340 nm. By scaling to σ(CH₃O₂)_{240 nm} = (4.24 ± 0.27) × 10^?18, the following absorption cross sections were determined: σ(HO₂)_{240 nm} = 1.29 ± 0.16, σ(C₂H₅O₂)_{240 nm} = 4.71 ± 0.45, σ(CH₃C(O)CH₂O₂)_{240 nm} = 2.03 ± 0.22, σ(CH₃C(O)CH₂O₂)_{230 nm} = 2.94 ± 0.29, and σ(CH₃C(O)CH₂O₂)_{310 nm} = 1.31 ± 0.15 (base e, units of 10^?18 cm² molecule^?1). To support the UV measurements, FTIR‐smog chamber techniques were employed to investigate the reaction of F and Cl atoms with acetone. The F atom reaction proceeds via two channels: the major channel (92% ± 3%) gives CH₃C(O)CH₂ radicals and HF, while the minor channel (8% ± 1%) gives CH₃ radicals and CH₃C(O)F. The majority (>97%) of the Cl atom reaction proceeds via H atom abstraction to give CH₃C(O)CH₂ radicals. The results are discussed with respect to the literature data concerning the UV absorption spectra of CH₃C(O)CH₂O₂ and other peroxy radicals. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 283–291, 2002     

Theoretical study on the mechanism of the (3)CH(2) + NO(2) reaction

The complex doublet potential energy surface of the CH(2)NO(2) system is investigated at the B3LYP/6-31G(d,p) and QCISD(T)/6-311G(d,p) (single-point) levels to explore the possible reaction mechanism of the triplet CH(2) radical with NO(2). Forty minimum isomers and 92 transition states are located. For the most relevant reaction pathways, the high-level QCISD(T)/6-311 + G(2df,2p) calculations are performed at the B3LYP/6-31G(d,p) geometries to accurately determine the energetics. It is found that the top attack of the (3)CH(2) radical at the N-atom of NO(2) first forms the branched open-chain H(2)CNO(2) a with no barrier followed by ring closure to give the three-membered ring isomer cC(H(2))ON-O b that will almost barrierlessly dissociate to product P(1) H(2)CO + NO. The lesser followed competitive channel is the 1,3-H-shift of a to isomer HCN(O)OH c, which will take subsequent cis-trans conversion and dissociation to P(2) OH + HCNO. The direct O-extrusion of a to product P(3) (3)O + H(2)CNO is even much less feasible. Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the title reaction is expected to be rapid, as is consistent with the measured large rate constant at room temperature. Formation of the other very low-lying dissociation products such as NH(2) + CO(2), OH + HNCO and H(2)O + NCO seems unlikely due to kinetic hindrance. Moreover, the (3)CH(2) attack at the end-O of NO(2) is a barrier-consumed process, and thus may only be of significance at very high temperatures. The reaction of the singlet CH(2) with NO(2) is also briefly discussed. Our calculated results may assist in future laboratory identification of the products of the title reaction.     

Theoretical studies on the reaction mechanism of CH2CH radical with HNCO

The reaction mechanism of CH₂CH radical with HNCO has been investigated systematically by density functional theory (DFT). The geometries and harmonic frequencies of reactants, intermediates, transition states, and products have been optimized with the B3LYP at different levels. At the same time, AIM is performed to calculate the charge density of some bonding critical points and the charges of some atoms. Nine feasible reaction pathways have been investigated. The results indicated that the main pathway is CH₂CH + HNCO → IMA1 → TSA1 → CH₂CH₂ + NCO, which is characterized by hydrogen atom transferring. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

In situ ATR-IR study of prochiral 2-methyl-2-pentenoic acid adsorption on Al2O3 and Pd/Al2O3

Adsorption and desorption of trans-2-methyl-2-pentenoic acid (MPeA) in dichloromethane (CH(2)Cl(2)) were investigated by using in situ attenuated total reflection infrared (ATR-IR) spectroscopy. A liquid flow-through spectroscopic cell allowed for high quality spectra to be obtained from deposited thin films of Al(2)O(3) and 1 wt% Pd/γ-Al(2)O(3) on a ZnSe internal reflection element. The MPeA molecules adsorb on both Al(2)O(3) and Pd surfaces molecularly and dissociatively under the concentration range examined (2-16 mM). In the case of molecular adsorption, both monomer (ν(C=O) ~ 1720 cm(-1)) and dimer (ν(C=O) ~ 1685 cm(-1)) species are observed to adsorb, with the relative amount of monomer to dimer dependent on the surface and the liquid phase acid concentration. In the case of dissociative adsorption, the acid adsorbs predominantly in a bridged bidentate configuration, as adjudged by the ca. 150-220 cm(-1) separation between asymmetric and symmetric vibrational bands. All of these species are found to be strongly adsorbed on both Al(2)O(3) and 1 wt% Pd/γ-Al(2)O(3) surfaces, even under pure solvent flow after adsorption.     

H原子和(CH3)2SiH2抽提反应的理论研究

采用UMP2/6-31G(d)理论水平优化了H原子和(CH3)2SiH2抽提反应势能面上的所有驻点,并在此水平基础上进行了内禀反应坐标(IRC)的计算,得到该反应的反应途径(MEP)。应用变分过渡态理论及最小能量途径半经典绝热基态隧道效应校正(MEPSAG)、小曲率半经典绝热基态隧道效应校正(SCSAG)等方法对上述反应进行了动力学研究,期望从理论上提供一套温度范围较宽、精度较高的动力学数据,为阐明反应机理和解释实验结果提供理论依据。     

Br+CH3S(O)CH3反应机理的直接动力学研究

采用直接动力学的方法，对多通道反应体系Br＋CH3S（O）CH3进行了理论研究．在BH＆H-LYP／6-311G（2d，2p）水平下获得了优化几何构型、频率及最小能量路径（MEP），能量信息的进一步确认在MC-QCISD（单点）水平下完成．利用正则变分过渡态理论，结合小曲率隧道效应校正（CVT／SCT）方法计算了该反应的两个可行的反应通道在200K～2000K温度范围内的速率常数．在整个反应区间内，生成HBr的反应通道与生成CHa的反应通道存在着竞争，前者是主反应通道，后者是次反应通道．变分效应和小曲率隧道效应对反应速率常数的计算影响都很小．理论计算得到的两个反应通道的反应速率常数与实验值符合得很好．     

Preparation of CH3TiF and (CH3)2TiF2 from the reaction of CH(3)F with laser-ablated Ti atoms

Laser-ablated Ti atoms react with CH(3)F upon condensation with excess argon to form primarily CH(3)TiF and (CH(3))(2)TiF(2). Irradiation in the UV region promotes alpha-hydrogen rearrangement of CH(3)TiF to CH(2)=TiHF and increases the yield of (CH(3))(2)TiF(2). Annealing to allow diffusion and reaction of more CH(3)F markedly increases the yield of (CH(3))(2)TiF(2). This shows that the CH(3)TiF + CH(3)F reaction is spontaneous and that triplet state CH(3)TiF is an extremely reactive molecule. B3LYP calculations are extremely effective in predicting vibrational frequencies and isotopic shifts for CH(3)TiF and (CH(3))(2)TiF(2) and thus in confirming their identification from matrix infrared spectroscopy.     

Ab initio characterization of (CH3IO3) isomers and the CH3O2 + IO reaction pathways

The geometries, harmonic vibrational frequencies, relative energetics, and enthalpies of formation of (CH(3)IO(3)) isomers and the reaction CH(3)O(2) + IO have been investigated using quantum mechanical methods. Optimization has been performed at the MP2 level of theory, using all electron and effective core potential, ECP, computational techniques. The relative energetics has been studied by single-point calculations at the CCSD(T) level. Methyl iodate, CH(3)OIO(2), is found to be the lowest-energy isomer showing particular stabilization. The two nascent association minima, CH(3)OOOI and CH(3)OOIO, show similar stabilities, and they are considerably higher located than CH(3)OIO(2). Interisomerization barriers have been determined, along with the transition states involved in various pathways of the reaction CH(3)O(2) + IO.     

Study on the mechanism of catalytic synthesis of dimethyldichlorosilane by AlCl3/MIL‐53(Al)@γ‐Al2O3

Dimethyldichlorosilane, one of the most consumed organosilicon monomers in the industry, can be prepared in a highly efficient and environmentally friendly synthesis method of disproportionating methylchlorosilanes. However, the internal mechanism of the reaction remains unclear. In this paper, the mechanism catalyzed by AlCl₃/MIL‐53(Al) and AlCl₃/MIL‐53(Al)@γ‐Al₂O₃ catalysts was calculated at B3LYP/6‐311++G(3df, 2pd) level by using the density functional theory (DFT). The results showed that although the two catalysts had similar active structures, the catalytic effects were significantly different. The Lewis acid center on the surface of γ‐Al₂O₃ in the core‐shell catalyst is complementary to the classic Lewis acid AlCl₃ through the spatial superposition effect, which greatly improves the Lewis acid catalytic activity of AlCl₃/MIL‐53(Al)@γ‐Al₂O₃.     

The effects of water vapor on the CH3O2 self-reaction and reaction with HO2

The gas phase reactions of CH3O2 + CH3O2, HO2 + HO2, and CH3O2 + HO2 in the presence of water vapor have been studied at temperatures between 263 and 303 K using laser flash photolysis coupled with UV time-resolved absorption detection at 220 and 260 nm. Water vapor concentrations were quantified using tunable diode laser spectroscopy operating in the mid-IR. The HO2 self-reaction rate constant is significantly enhanced by water vapor, consistent with what others have reported, whereas the CH3O2 self-reaction and the cross-reaction (CH3O2 + HO2) rate constants are nearly unaffected. The enhancement in the HO2 self-reaction rate coefficient occurs because of the formation of a strongly bound (6.9 kcal mol(-1)) HO2 x H2O complex during the reaction mechanism where the H2O acts as an energy chaperone. The nominal impact of water vapor on the CH3O2 self-reaction rate coefficient is consistent with recent high level ab initio calculations that predict a weakly bound CH3O2 x H2O complex (2.3 kcal mol(-1)). The smaller binding energy of the CH3O2 x H2O complex does not favor its formation and consequent participation in the methyl peroxy self-reaction mechanism.     

Theoretical dynamic studies on the reaction of CH3C(O)CH3-nFn with the hydroxyl radical and the chlorine atom.

The mechanisms of the reactions: CH(3)C(O)CH(2)F+OH/Cl-->products (R1/R2) and CH(3)C(O)CF(3)+OH/Cl-->products (R3/R4) are studied over a wide temperature range (200-2000 K) by means of the dual-level direct dynamics method. The optimized geometries and frequencies of the stationary points are calculated at the MP2/cc-pVDZ and B3LYP/6-311G(d,p) levels. The energy profiles of the reactions are then refined with the interpolated single-point-energy method (ISPE) at the BMC-CCSD level. The canonical variational transition-state theory (CVT) with the small-curvature-tunneling (SCT) correction method is used to calculate the rate constants. Using group-balanced isodesmic reactions as working chemical reactions, the standard enthalpies of formation for CH(3)C(O)CH(2)F, CH(3)C(O)CF(3), CH(3)C(O)CHF, CH(2)C(O)CH(2)F, and CH(2)C(O)CF(3) are evaluated at the CCSD(T)/6-311+G(2d,p)//MP2/cc-pVDZ level of theory. The results indicate that the hydrogen abstraction is dominated by removal from the fluoromethyl position rather than from the methyl position.     

Investigation of the radical product channel of the CH(3)C(O)CH(2)O(2) + HO(2) reaction in the gas phase

The reaction of CH(3)C(O)CH(2)O(2) with HO(2) has been studied at 296 K and 700 Torr using long path FTIR spectroscopy, during photolysis of Cl(2)/acetone/methanol/air mixtures. The branching ratio for the reaction channel forming CH(3)C(O)CH(2)O, OH and O(2) () was investigated in experiments in which OH radicals were scavenged by addition of benzene to the system, with subsequent formation of phenol used as the primary diagnostic for OH radical formation. The observed prompt formation of phenol under conditions when CH(3)C(O)CH(2)O(2) reacts mainly with HO(2) indicates that this reaction proceeds partially by channel , which forms OH both directly and indirectly, by virtue of secondary generation of CH(3)C(O)O(2) (from CH(3)C(O)CH(2)O) and its reaction with HO(2) (). The secondary generation of OH radicals was confirmed by the observed formation of CH(3)C(O)OOH, a well-established product of the CH(3)C(O)O(2) + HO(2) reaction (via channel ). A number of delayed sources of OH also contribute to the observed phenol formation, such that full characterisation of the system required simulations using a detailed chemical mechanism. The dependence of the phenol and CH(3)C(O)OOH yields on the initial peroxy radical precursor reagent concentration ratio, [methanol](0)/[acetone](0), were well described by the mechanism, consistent with a small but significant fraction of the reaction of CH(3)C(O)CH(2)O(2) with HO(2) proceeding via channel . This allowed a branching ratio of k(3b)/k(3) = 0.15 +/- 0.08 to be determined. The results therefore provide strong indirect evidence for the participation of the radical-forming channel of the title reaction.     

Crossed-beam dynamics studies of the radical-radical combustion reaction O((3)P) + CH3 (methyl)

The dynamics of the radical-radical reaction O((3)P) + CH(3), a prototypical case for the reactions of atomic oxygen with alkyl radicals of great relevance in combustion chemistry, has been investigated by means of the crossed molecular beam technique with mass spectrometric detection at a collision energy of 55.9 kJ mol(-1). The results have been examined in the light of previous kinetic and theoretical work. From product angular and velocity distribution measurements, the dynamics of the predominant H-displacement channel leading to formaldehyde formation has been characterized. This channel has been found to proceed via the formation of an osculating complex; a significant coupling between the product centre-of-mass angular and translational energy distributions has been noted. Experimental attempts to characterize the dynamics of the channel leading to HCO + H(2) have failed and it remains unclear whether HCO is formed by the reaction and/or, if formed, a part of HCO does not dissociate quickly into CO + H.