Adsorption of water and methanol on GaAs(110) surfaces studied by ultraviolet photoemission

UV photoemission spectroscopy (UPS) with He 1 radiation (hν = 21.2 eV) has been used to study the interaction of H₂O and CH₃OH with GaAs(110) surfaces prepared by cleavage in ultrahigh vacuum (UHV). For H₂O two molecularly adsorbed phases can be distinguished at 300 K: at low coverage H₂O is chemisorbed by its oxygen lone-pair orbital to the surface whereas for higher exposures a less perturbed species which resembles more a “physisorbed” or condensed H₂O layer is found. At 180 K only the less perturbed species can be identified. Also CH₃OH is chemisorbed molecularly at lower coverage with its oxygen end to the GaAs surface. For higher exposures two additional emission bands are observed which are interpreted as due to the methoxy radical CH₃O resulting from a partial decomposition of CH₃OH.     

CH3OH在ZnO(0001)表面的光催化解离

本文利用266 nm波长的激光及程序升温脱附的方法研究了甲醇在ZnO(0001)表面的光催化反应. TPD结果显示部分的CH₃OH以分子的形式吸附在ZnO(0001)表面,而另外一部分在表面发生了解离. 实验过程中探测到H₂,CH₃^·,H₂O,CO,CH₂O,CO₂和CH₃OH这些热反应产物. 紫外激光照射实验结果表明光照可以促进CH₃OH/CH₃O^·解离形成CH₂O,在程序升温或光照的过程中它又可以转变为HCOO^-. CH₂OH_Zn与OH_ad反应在Zn位点上形成H₂O分子. 升温或光照都能促进CH₃O^·转变为CH₃^·. 该研究对CH₃OH在ZnO(0001)表面的光催化反应机理提供了一个新的见解.     

A statistical model for the product energy distribution in reactions leading to prompt dissociation

Direct dynamics calculations have been performed for three reactions: C₃H₈ + H → i-C₃H₇ + H₂, C₃H₈ + H → n-C₃H₇ + H₂, and C₂H₃ + O₂ → HCO + CH₂O. The fraction of the population for the radical products that promptly dissociates is computed. The results for C₃H₈ + H are qualitatively similar to previous results for C₃H₈ + OH, but the new results exhibit a slightly higher branching fraction for prompt dissociation products, owing to the fact that a greater fraction of the internal energy in the transition state ends up in the radical. For C₂H₃ + O₂ → HCO + CH₂O, the fraction of HCO that promptly dissociates is in excess of 99%. Consequently, the main product for C₂H₃ + O₂ at lower temperatures should be written as H + CO + CH₂O and not HCO + CH₂O. These results are then compared with four previous systems: CH₂O + H → HCO + H₂, CH₂O + OH → HCO + H₂O, C₃H₈ + OH → i-C₃H₇ + H₂O, and C₃H₈ + OH → n-C₃H₇ + H₂O. Based upon these seven system, several statistical models are presented. The goal of these statistical models is to predict the fraction of the transition state energy that ends up in the rovibrationally excited radical. On average, these statistical models provide an excellent prediction of product energy distribution. Consequently, these models can be used instead of costly trajectory simulations for predicting prompt radical dissociation for larger species.     

Flame structure of laminar premixed anisole flames investigated by photoionization mass spectrometry and photoelectron spectroscopy

Two laminar, premixed, fuel-rich flames fueled by anisole-oxygen-argon mixtures with the same cold gas velocity and pressure were investigated by molecular-beam mass spectrometry at two synchrotron sources where tunable vacuum-ultraviolet radiation enables isomer-resolved photoionization. Decomposition of the very weak O–CH₃ bond in anisole (C₆H₅OCH₃) by unimolecular decomposition yields the resonantly-stabilized phenoxy radical (C₆H₅O). This key intermediate species opens reaction routes to five-membered ring species, such as cyclopentadiene (C₅H₆) and cyclopentadienyl radicals (C₅H₅). Anisole is often discussed as model compound for lignin to study the phenolic-carbon structure in this natural polymer. Measured temperature profiles and mole fractions of many combustion intermediates give detailed information on the flame structure. A very comprehensive reaction mechanism from the literature which includes a sub-scheme for anisole combustion is used for species modeling. Species with the highest measured mole fractions (on the order of 10^?3–10^?2) are CH₃, CH₄, C₂H₂, C₂H₄, C₂H₆, CH₂O, C₅H₅ (cyclopentadienyl radical), C₅H₆ (cyclopentadiene), C₆H₆ (benzene), C₆H₅OH (phenol), and C₆H₅CHO (benzaldehyde). Some are formed in the first destruction steps of anisole, e.g., phenol and benzaldehyde, and their formation will be discussed and with regard to the modeling results. There are three major routes for the fuel destruction: (1) formation of benzaldehyde (C₆H₅CHO), (2) formation of phenol (C₆H₅OH), and (3) unimolecular decomposition of anisole to phenoxy (C₆H₅O) and CH₃ radicals. In the experiment, the phenoxy radical could be measured directly. The phenoxy radical decomposes via a bicyclic structure into the soot precursor C₅H₅ and CO. Formation of larger oxygenated species was observed in both flames. One of them is guaiacol (2-methoxyphenol), which decomposes into fulvenone. The presented speciation data, which contain more than 60 species mole fraction profiles of each flame, give insights into the combustion kinetics of anisole.     

对典型多通道反应H+CH3OH的模式特异动力学研究

H+CH₃OH作为典型的多通道反应,在燃烧和星际中起着重要的作用. 本文基于在UCCSD(T)-F12a/AVTZ水平上计算的大量数据点,构建了该体系的全维精确势能面,并基于该势能面,研究了不同产物通道的模式特异动力学. 结果表明,O-H 伸缩、沿C-O轴的扭转以及C$-$H伸缩等模式的振动激发对H₂+CH₃O、H₂+CH₂OH、H₂O+CH₃和H+CH₃OH四个产物通道有着不同的影响. 该研究有助于理解具有多个产物通道的复杂反应的模式特异动力学,进而帮助控制其竞争反应.     

A first-principles study on the adsorption behaviour of methanol and ethanol over C59B heterofullerene

In the present study, the adsorption behaviour of methanol (CH₃OH) and ethanol (C₂H₅OH) molecules over heterofullerene C₅₉B surface is studied by density functional theory calculations. This heterofullerene is obtained from C₆₀ by substituting a carbon atom with a boron atom and relaxing self-consistently the structure to the local minimum. The adsorption of CH₃OH and C₂H₅OH on the C₅₉B is exothermic and the relaxed geometries are stable. The CH₃OH and C₂H₅OH adsorption can also induce a change in the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy gap of the nanocage. The dehydrogenation pathways of CH₃OH and C₂H₅OH via O–H and C–H bonds scission are also examined. The results indicate that O–H bond scission is the most favourable pathway on the C₅₉B surface.     

Electron impact spectra of some alkyl derivatives of water and related compounds

Electron impact energy loss spectra at impact energies of 100 eV and 50 eV and a scattering angle of 2 degrees are presented for alkyl derivatives of H₂O and related compounds. Spectra of H₂O, CH₃OH, CH₃OCH₃, ethylene oxide, CH₃CH₂OH, (CH₃)₂CHOH, (CH₃)₃C C₂H₅OC₂H₅ and tetrahydrofuran are tentatively assigned using derived term values and ionization potentials from photoelectron spectrosc Substituent effects on Rydberg orbital energies are discussed using Taft σ* values.     

Description of the spectrum of the ethanol molecule with allowance for the torsional motions of its hydroxyl and methyl groups

On the basis of symmetry methods, a rigorous model is, for the first time, obtained for describing the spectrum of the ethanol molecule CH₃CH₂OH in a given vibronic state with allowance for the simultaneous torsional motion of the hydroxyl group OH and the methyl group CH₃.     

Matrix isolation study of the vacuum-ultraviolet photolysis of methanol: The infrared spectrum of the CH2OH free radical

Infrared studies of the products of the 1470 Å photolysis of normal and isotopically substituted methanol isolated in argon and nitrogen matrices at 14°K have provided evidence for the stabilization of a significant yield of CH₂OH. Assuming a slightly nonplanar structure for the molecule, it has been possible to obtain an approximate valence-force potential field which provides a reasonable fit to virtually all of the data. The CO bond of CH₂OH is slightly stronger than that of methanol, and the torsional barrier is significantly greater, in accord with previous electron spin resonance observations. There is no evidence for the production or stabilization of CH₃O in the matrix. CH₂OH undergoes photodecomposition upon exposure to radiation in the 2300–2800 Å spectral region, leading to a growth in the HCO absorptions.     

Townsend-Koeffizient α für Alkoholdämpfe,Luft und Argon

Measurements of the first Townsend coefficient for the vapours of CH₃OH, C₂H₅OH, C₃H₇OH(n), C₃H₇OH(iso) are described. The experimental arrangement is tested by measuring the known values of air and argon.     

Temperature and carbon source effects on methane–air flame synthesis of CNTs

We have conducted experimental and numerical studies on flame synthesis of carbon nanotubes (CNTs) to investigate the effects of three key parameters – selective catalyst, temperature and available carbon sources – on CNT growth. Two different substrates were used to synthesize CNTs: Ni-alloy wire substrates to obtain curved and entangled CNTs and Si-substrates with porous anodic aluminum oxide (AAO) nanotemplates to grow well-aligned, self-assembled and size-controllable CNTs, each using two different types of laminar flames, co-flow and counter-flow methane–air diffusion flames. An appropriate temperature range in the synthesis region is essential for CNTs to grow on the substrates. Possible carbon sources for CNT growth were found to be the major species CO and those intermediate species C₂H₂, C₂H₄, C₂H₆, and methyl radical CH₃. The major species H₂, CO₂ and H₂O in the synthesis region are expected to activate the catalyst and help to promote catalyst reaction.     

ESCA: A theoretical intensity model based on the plane-wave approximation

In this paper, we first of all present a rather simple and convenient theoretical equation, based upon the plane-wave approximation, for the differential cross-section for photoionization of a polyatomic molecule. Next, we derive an intensity model specific for X-ray photoelectron spectra of a general molecule containing first-row atoms. Applications of the model to CH₄, H₂O, N₂, CO, CF₄, and CH₃OH give very satisfactory results compared with experimental ESCA relative intensities. Similarities and differences between our theoretical model and Gelius' semiempirical model are pointed out and discussed.     

Far infrared laser lines produced by methanol and its isotopic species: A review

Methanol (CH₃OH) is considered today one of the most important active media for the generation of laser radiation in the far-infrared (FIR) spectral region. Together with ten of its other isotopic species, it is responsible for the major part of the laser lines generated by the optical pumping technique. Due to the extreme importance of those molecules as laser generators, we understood that there was a necessity of a comprehensive work which would include as much pratical information as possible about each line.Chang et al⁽¹⁾ early recognized methanol as a source of strong FIR laser lines. Since then, more than 100 papers were published containing information about new laser emission. Recently, Moruzzi et al⁽¹¹⁴⁾ presented a review of 575 lines produced by¹²CH₃OH. In the present paper, we have extended the review to the various isotopic modifications of this molecule (namely¹³CH₃OH, CD₃OH,¹³CD₃OH, CD₃OD,¹³CD₃OD, CH₃OD, CH ₃ ¹⁸ OH, CH₂DOH, CH₂DOD and CHD₂OH), a total of nearly 2000 lines with wavelengths ranging from 19µm to 3030µm.     

Two-dimensional condensation of water and alcohols on NaF

On the surface of NaF the adsorption isotherms of H₂O, D₂O, CH₃OH, C₃H₃OH and 1-C₃H₇OH as well as the infrared spectra of H₃O, D₂O, dilute HDO, CH₃OH and CH₃OD were measured. The adsorption temperatures of H₃O (253–308 K) were within the phase transition region where two phases of low and high density coexist, while those of CH₃OH, C₂H₅OH and 1-C₃H₃OH were yet within a super-critical region. The entropy of the 2D condensed H₂O on NaF was found to be 14.0 cal K^?1 mol^?1, which suggests that the condensed phase of water on NaF is liquid-like. The OD stretching band of dilute HDO in the 2D condensed water gives a maximum adsorption at ca. 2530 cm^?1 with a half width of ca. 150 cm^?1, being in good agreement with that in liquid water. Comparison of the integrated absorbance of the D₂O bending mode with that of the OD stretching mode suggests that the cluster size of the 2D condensed water on NaF decreases with increasing temperature. The 2D critical temperature and the occupied areas of these adsorbates enable us to conclude that the compatibility of the molecular size with the surface lattice is not important in the occurrence of the 2D condensation of the hydrogen-bonding molecules on NaF and that adsorbed molecules are randomly oriented on the surface to the extent similar to that in 3D liquid state.     

Reaction intermediates of methanol synthesis and the water–gas-shift reaction on the ZnO(0001) surface

The polar Zn-ZnO(0001) surface is involved in the catalysis of methanol synthesis and the water–gas-shift reaction. We use density functional theory calculations to explore the favorable binding geometries and energies of adsorption of several molecular species relevant to these reactions, namely carbon monoxide (CO), carbon dioxide (CO₂), water (H₂O) and methanol (CH₃OH). We also consider several proposed reaction intermediates, including hydroxymethyl (CH₂OH), methoxyl (CH₃), formaldehyde (CH₂O), methyl (CH₃), methylene (CH₂), formic acid (HCOOH), formate (HCOO), formyl (HCO), hydroxyl (OH), oxygen (O) and hydrogen (H). For each, we identify the preferred binding geometry at a coverage of 1/4 monolayers (ML), and report calculated vibrational frequencies that could aid in the identification of these species in experiment. We further explore the effects on the binding energy when the adsorbate coverage is lowered to 1/9 and 1/16 ML.     

DSC studies of neohexanol and its isomers

DSC method has been used to establish a solid state polymorphism of four dimethyl butanols having CH₃ side groups: 2,2-dimethyl-1-butanol [CH₃CH₂C(CH₃)₂CH₂OH)], 3,3-dimethyl-1-butanol [(CH₃)₃CCH₂CH₂OH], 3,3-dimethyl-2-butanol [(CH₃)₃CCH(OH)CH₃] and 2,3-dimethyl-2-butanol [(CH₃)₂CHCOH(CH₃)₂]. Three isomers appear to be glass formers. Glass of liquid phase has been observed for 3,3-DM-1-B while glass of plastic phase for 2,2-DM-1-B and 3,3-DM-2-B. For 2,3-DM-2-B on cooling only crystallization has been found. Influence of location of the OH group in molecule on polymorphism is discussed. IR-spectra, measured in the liquid phase, have revealed hydrogen bonds in all isomers.     

Thermal activation and reaction of allyl alcohol on Ni(100)

The thermal chemistry of allyl alcohol (CH₂CHCH₂OH) on a Ni(100) single-crystal surface was studied by the temperature programmed desorption (TPD) and the X-ray photoelectron spectroscopy (XPS). The allyl alcohol adsorbs molecularly on the metal surface at 100 K. Intact molecular desorption from the surface occurs at temperatures around 180 K, but some molecules exhibit chemical reactivity on the surface: activation of the OH, CC, and CO bonds produces η¹(O)-allyloxy CH₂CHCH₂O_(a), η²(C, C) allyl alcohol (C_(a)H₂C_(a)HCH₂OH), and η³(C, C, O)-alkoxide (C_(a)H₂C_(a)CH₂ O_(a)) intermediates. Further thermal activation of allyl alcohol on the surface yields propylene (CH₂CHCH₃), 1-propanol (CH₃CH₂CH₂OH), propanal (CH₃CH₂CHO), and combustion and dehydrogenation products (H₂O, H₂, and CO). Propylene desorbs from the surface at temperatures of around 270 K. Hydrogenation to the η³(C, C, O)-alkoxide intermediate leads to the production of propanal which desorbs from the surface around 320 K, while hydrogenation of the η²(C, C) allyl alcohol intermediate produces 1-propanol, which desorbs at around 310 K. The co-adsorption of hydrogen atoms on the surface enhances the formation of the saturated alcohol, while co-adsorption of oxygen enhances the formation of both the saturated alcohol and the saturated aldehydes.     

全维高精度势能面上F+CH3OH反应的产物振动态分布

甲醇与氟原子之间的抽氢反应可以生成HF和CH₃O、CH₂OH自由基等产物. 该反应在环境化学、燃烧化学、辐射化学和星际化学中都非常重要. 基于之前构建的全维高精度势能面,本文采用准经典轨线方法研究了该典型反应的动力学. 特别是使用正则模式分析方法确定了多原子产物CH₃O和CH₂OH的振动态分布. 研究发现,当反应物处于振转基态时,CH₃O和CH₂OH主要分布在基态. 当反应物CH₃OH的OH伸缩模式激发为第一激发态时,产物CH₂OH的OH伸缩模式、扭转模式、H₂CO 面外弯曲模式及其组合会被有效激发. 在两条通道中,可用能量大部分都流入HF的振动能和产物的平动能,而自由基产物CH₃O或CH₂OH只得到非常少的能量,与实验结果一致,这也表明了自由基的旁观者性质.     

The catalytic effects of H2CO3, CH3COOH,HCOOH and H2O on the addition reaction of CH2OO + H2O → CH2(OH)OOH

The addition reaction of CH₂OO + H₂O → CH₂(OH)OOH without and with X (X = H₂CO₃, CH₃COOH and HCOOH) and H₂O was studied at CCSD(T)/6-311+ G(3df,2dp)//B3LYP/6-311+G(2d,2p) level of theory. Our results show that X can catalyse CH₂OO + H₂O → CH₂(OH)OOH reaction both by increasing the number of rings, and by adding the size of the ring in which ring enlargement by COOH moiety of X inserting into CH₂OO···H₂O is favourable one. Water-assisted CH₂OO + H₂O → CH₂(OH)OOH can occur by H₂O moiety of (H₂O)₂ or the whole (H₂O)₂ forming cyclic structure with CH₂OO, where the latter form is more favourable. Because the concentration of H₂CO₃ is unknown, the influence of CH₃COOH, HCOOH and H₂O were calculated within 0–30 km altitude of the Earth's atmosphere. The results calculated within 0–5 km altitude show that H₂O and HCOOH have obvious effect on enhancing the rate with the enhancement factors are, respectively, 62.47%–77.26% and 0.04%–1.76%. Within 5–30 km altitude, HCOOH has obvious effect on enhancing the title rate with the enhancement factor of 2.69%–98.28%. However, compared with the reaction of CH₂OO + HCOOH, the rate of CH₂OO···H₂O + HCOOH is much slower.     

Description of the spectrum of the ethanol molecule with allowance for the mixing of its trans and gauche conformers

Based on symmetry methods, a rigorous model is, for the first time, obtained for describing the spectrum of the ethanol molecule CH₃CH₂OH in a given vibronic state with allowance for the mixing of its trans and gauche conformers due to the torsional motion of the hydroxyl group OH.