Energy distributions of gallium nanoclusters

Starting with the heat-capacity data of Breaux et al., [J. Am. Chem. Soc. 126, 8629 (2004)] we use the maximum-entropy method to calculate energy distribution functions for gallium-ion nanoclusters over a wide temperature range (100-1050 K). Specifically, we calculate energy distributions for clusters containing n = 39 and n = 45 gallium atoms. For the case of n = 39 clusters the energy distribution gets systematically broader as a function of temperature with no indication of any marked structural change in the cluster. On the other hand, the energy distribution for the n = 45 cluster first gets broader as a function of temperature but then gets narrower again as the temperature is further increased, indicating that there is some kind of structural transition taking place in this cluster species.     

Energy distributions in multiple photon absorption experiments

Photofragmentation experiments on molecules and clusters often involve multiple photon absorption. The distributions of the absorbed number of photons are frequently approximated by Poisson distributions. For realistic laser beam profiles, this approximation fails seriously due to the spatial variation of the mean number of absorbed photons across the laser beam. We calculate the distribution of absorbed energy for various laser and molecular-beam parameters. For a Gaussian laser beam, the spatially averaged distributions have a power-law behavior for low energy with a cutoff at an energy which is proportional to fluence. The power varies between -1 for an almost parallel laser beam and -5/2 for a divergent beam (on the scale of the molecular beam). We show that the experimental abundance spectra of fullerenes and small carbon clusters can be used to reconstruct the distribution of internal energy in the excited C60 molecule prior to fragmentation and find good agreement with the calculated curves.     

Energy level distributions in spectra of coupled harmonic oscillators

The spectral density distribution of a hamiltonian which represents a system of N coupled harmonic oscillators, and hence may approximately describe molecular vibrations in the local mode picture, is analyzed. The spectral density moments are expressed as linear combination of products of coefficients which depend on the molecular structure and of one-particle moments describing individual bonds and interactions between them. Detailed expressions for linear and tetrahedral molecules are analyzed. Moreover, general formulae for matrix elements of powers of momentum in the harmonic oscillator basis are given.     

空气中电晕放电高能电子密度沿反应器分布的光谱研究(英)

利用目前在等离子体特性诊断方面较为先进实用的发射光谱法,在常温常压下测量了正脉冲电晕放电空气中的Ｎ２（Ｃ３ Πｕ →Ｂ３ Πｇ） 发射光谱相对强度沿线－ 筒式反应器的径向分布,由此得到了正脉冲电晕放电等离子体中高能电子（ ≥１１ ．０３ｅＶ） 的电子密度沿线－ 筒式反应器的径向分布．随径向距离增大高能电子密度呈非线性递减,对于不同放电电压这种递减规律相同．     

Electronic sputtering produced by fission fragments on condensed CO and CO2

Condensed CO and CO2 are bombarded by approximately 65 MeV 252Cf fission fragments and the desorbed ions are analyzed by time-of-flight mass spectrometry as a function of target temperature, in the ranges 25-33 K and 75-91 K, respectively. Absolute desorption yields are measured up to complete ice sublimation. The mass spectra of both ice targets reveal the emission of: (1) low mass ions, produced by direct Coulomb interaction of the highly charged projectiles and delta-electrons with CO and CO2, and (2) pronounced series of cluster ions. The basic ice cluster structures (CO)n and (CO2)n are present in the emitted cluster series such as (CO)nCO+, (CO2)nCO2+, or (CO2)nCO3-. In the case of CO ice, however, the intense production of the series Cn+, Cn-, and (CO)mCn+ shows that Cn is the main cluster structure, consequence of a higher concentration of free carbon atoms in the nuclear track plasma of CO ice than in that of CO2 ice. Ion cluster abundance is observed to decrease exponentially with cluster mass. The decay constant is k(n) congruent with 0.13, about the same for series based on (CO)n and (CO2)n, but a factor 3.3 higher for the Cn series. The Cn clusters are formed by gas-phase condensation, but the (CO)n and (CO2)n clusters are produced by fracturing of the highly excited solid around the nuclear track. A dramatic reduction of the ion desorption yield is observed near T = 29 K for CO and near T = 85 K for CO2, when fast sublimation occurs and ice thickness vanishes. Close to sublimation temperature, the decay constant of the (CO)2Cn+ series increases due to a decreasing formation probability of large Cn clusters.     

A simplified representation of the potential produced by Gaussian charge distributions

A procedure is presented which allows a more economical representation of the potential produced by orbital charge distributions in which the orbitals are expanded in terms of a finite set of polynomial Gaussian functions. The basic idea is that the products of pairs of Gaussian basis functions, on which the charge distributions are expanded, are expressed in terms of a new basis set of optimally chosen single Gaussian functions. Such a procedure has been tested in a particular case and a few possible applications have been suggested.     

IR detection by matrix isolation technique of radicals produced in a silane discharge

Infrared absorption spectra of free radicals trapped in a solid argon matrix, after extraction from a low pressure silane plasma hot cathode discharge, have been clearly observed. First partial results concerning the assignments of the detected absorption peaks and the energy dependence of neutral fragmentation pattern of silane by electron impact are presented and discussed. Matrix isolation technique appears to be a promising tool to characterize neutral species in discharges devoted to thin film deposition.     

Decomposition of methane in an AC discharge

This paper presents qualitative and quantitative product analysis results from an atmospheric-pressure AC discharge of nitrogen containing trace levels of methane and oxygen. In the absence of oxygen the primary products were unreacted methane, hydrogen, and hydrogen cyanide. Methane destruction efficiency was unaffected by trace oxygen addition; however, hydrogen and hydrogen cyanide levels decreased and the concentrations of carbon monoxide, carbon dioxide, and water increased as the level of added oxygen increased. The only cyanide compound that persisted with air as the bulk gas was cyanogen. A chemical mechanism is presented which qualitatively explains the observed product distributions.NRC/NRL postdoctoral fellow.NRL research apprentice program, summer 1984.     

Isotope separation by a q-switched continuous discharge CO2 laser

For ¹³C isotope separation it is more economic to use a q-swiched CO₂ laser than a TEA laser. It is shown that 40 mJ pulses are needed for full use of photons. With a laser of 20 mJ, isotope selective dissociation of ¹³CHClF₂ and ³²SF₆ is demonstrated in this work.     

Dipole oscillator strength distributions,sums, and dispersion energy coefficients for CO and CO2

Globally reliable dipole oscillator strength distributions (DOSDs) have been constructed for ground state CO and CO₂ molecules; the DOSD for CO corresponds to photon energies greater than the electronic absorption threshold while that for CO₂ includes the infrared part of the spectra as well. The recommended DOSDs are used to evaluate the isotropic dipole—dipole dispersion energies for the COCO, COCO2 and CO2CO2 interactions as well as the molar refractivities, as a function of wavelength, and the dipole sums, S_k, k = 2(?1) -4, -6, -8, -10, for the two molecules. Pseudo-DOSD representations of the recommended DOSDs are provided which allow the efficient accurate evaluation of the dispersion energy coefficients C₆ for the interaction of CO or CO₂ with a variety of other atoms and molecules. Previous results for C₆ are found to be in disagreement with our recommended results for interactions involving CO₂. The results of this paper are used to give a reasonably general discussion of the difficulties associated with obtaining reliable results for C₆ by using Padé approximant bounding methods.     

State and velocity distributions of Cl atoms produced in the photodissociation of ICI at 237 nm

Photofragment spectroscopy of ICI molecules photodissociated at 237 nm is studied by 2 + 1 resonance-enhanced multi-photon ionization and time of flight techniques. Doppler profiles of the chlorine atom fragments in two spin—orbit states show that chlorine atoms in the ground state, ²P_3/2, are produced from a perpendicular dissociative transition, and chlorine atoms in the excited state, ²P , arise from a parallel transition. The possible electronically excited states leading to dissociation in both the perpendicular and parallel cases are considered.     

Intensity,temperature and density variations; their distributions and correlations in a spark discharge plasma

Spark discharges between Al and Al-Cu electrodes in air at atmospheric pressure were studied. The probability distributions of fluctuations of the temperature, the intensities of some spectral lines of AI III, Al II Cu II and N II ions and the densities of the relevant particles, as well as various correlation characteristics were measured. The relationship between the measured characteristics and plasma, and spectral-line parameters is discussed.     

Activated carbon produced from paulownia sawdust for high-performance CO2 sorbents

In this paper, activated carbons （ACs） with high specific surface areas were successfully synthesized by simple one-step carbonization-activation from paulownia sawdust biomass, and the effects of the synthetic conditions on their CO2 capture capacity were investigated as well. The results show that, when the mass ratio between activator and biomass is 4, the activation temperature is 700℃ and the activation time is 1 h, as-made AC provides the most micropores for CO2 adsorption. As a consequence, the maximum CO2 uptake of 8.0 mmol/g is obtained at 0 ℃ and 1 bar.     

Tracer kinetics of plants carbon allocation with continuously produced11CO2

Parameters of carbon allocation dynamics in plants were measured using¹¹CO₂ and tracer kinetics techniques. Mechanical agitation reduced carbon export rate by 33% in cotton seedling's leaf, while storage rate and export pool size increased. Carbon storage and export rates of C₄ bunch grasses were higher in the afternoon than in the morning inspite of the decrease in CER.Water stress of cotton seedlings caused reduction in carbon export rate, and increase in exportable products concentrations and rate of storage. By the third stress day, measurable decreases in CER, transpiration, export rate and export pool size were recorded.     

Temperature and velocity distributions in an inductively coupled plasma

Computer simulations of inductively coupled plasma discharges (ICP) with flow patterns similar to those found in spectrochemical analysis were reported previously. In this investigation temperature and velocity distributions are measured under conditions which allow direct comparison with computer calculations for pure argon central gas flows without solution aerosols. Based upon these comparisons, a refined ICP gas flow model is proposed and its application provides agreement within experimental error between measured and calculated velocity and temperature profiles in most regions of the discharge.     

太阳能驱动Ni-N掺杂多孔碳高效电催化还原CO2为CO

利用可再生能源将二氧化碳(CO2)电催化还原为有价值的化学品和燃料,不仅可缓解温室效应,而且可实现碳资源的循环利用。以蛋白胨与盐形成的凝胶为原料,经高温热解后制备了用于电还原CO2的Ni-N掺杂碳多孔催化剂。该催化剂表现出优异的电催化还原CO2为CO的性能,在电压为-0.66 V(vs.RHE)下,CO的法拉第效率为92.0%,过电位为550 mV,还原电流密度为2.5 mA·cm-2。该催化剂优异的CO2的电催化活性归因于其存在的Ni-N活性位点和高度多孔的结构。此外,利用太阳能电池产生的电能,该催化剂可持续进行CO2电催化还原为CO,为CO2的资源化利用提供了有价值的参考。