CH5+: the infrared spectrum observed

Protonated methane, CH5+, has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely. Although many theoretical papers have been published on the quantum mechanics of the system, a better understanding requires spectral data. A complex, high-resolution infrared spectrum of CH5+ corresponding to the C-H stretching band in the 3.4-micrometer region is reported. Although no detailed assignment of the individual lines was made, comparison with other carbocation spectra strongly suggests that the transitions are due to CH5+.     

Understanding the infrared spectrum of bare CH5+

Protonated methane, CH5+, continues to elude definitive structural assignment, as large-amplitude vibrations and hydrogen scrambling challenge both theory and experiment. Here, the infrared spectrum of bare CH5+ is presented, as detected by reaction with carbon dioxide gas after resonant excitation by the free electron laser at the FELIX facility in the Netherlands. Comparison of the experimental spectrum at approximately 110 kelvin to finite-temperature infrared spectra, calculated by ab initio molecular dynamics, supports fluxionality of bare CH5+ under experimental conditions and provides a dynamical mechanism for exchange of hydrogens between CH3 tripod positions and the three-center bonded H2 moiety, which eventually leads to full hydrogen scrambling. The possibility of artificially freezing out scrambling and internal rotation in the simulations allowed assignment of the infrared spectrum despite this pronounced fluxionality.     

Quantum Yield for Production of CH3NC in the Photolysis of CH3NCS

The ultraviolet spectrum of methyl isothiocyanate (CH(3)NCS) and the quantum yield for its dissociation into methyl isocyanide (CH(3)NC) and atomic sulfur at 308 nanometers, Phi = 0.98 +/- 0.24, were measured. Methyl isothiocyanate is widely used as an agricultural fumigant and readily enters the atmosphere during and after application. The results indicate that photodissociation by sunlight is an effective pathway for its removal from the atmosphere.     

Gas-phase infrared spectrum of the protonated water dimer

The protonated water dimer is a prototypical system for the study of proton transfer in aqueous solution. We report infrared photodissociation spectra of cooled H+(H2O)2 [and D+(D2O2] ions, measured between 620 and 1900 wave numbers (cm-1). The experiment directly probes the shared proton region of the potential energy surface and reveals three strong bands below 1600 cm-1 and one at 1740 cm-1 (for H5O2+). From a comparison to multidimensional quantum calculations, the three lower energy bands were assigned to stretching and bending fundamentals involving the O...H+...O moiety, and the highest energy band was assigned to a terminal water bend. These results highlight the importance of intermode coupling in shared proton systems.     

First-principles theory for the H + CH4 --> H2 + CH3 reaction

A full-dimensional quantum dynamics simulation of a hydrogen atom reacting with methane on an accurate ab initio potential energy surface is reported. Based on first-principles theory, thermal rate constants are predicted with an accuracy comparable to (or even exceeding) experimental precision. The theoretical prediction is within the range of the significantly varied experimental rate constants reported by different groups. This level of accuracy has previously been achieved only for smaller, three-or four-atom reactive systems. Comparison with classical transition state theory confirms the importance of quantum mechanical tunneling for the rate constant below 400 kelvin.     

绿色快速分析技术--近红外及其应用

介绍了近红外光谱快速分析技术的特点。以其在农业、加工业和烟草等行业中的具体应用说明近红外光谱分析技术及其快速、无污染、无需前处理、非破坏性及多组分同时定量分析等优势所产生的巨大社会效益和经济效益。     

Rotationally resolved infrared spectrum of the charge transfer complex [Ar-N2]+

Difficulties in preparing cluster ions for spectroscopic studies have limited our understanding of intermolecular forces in charged complexes that are typical of many reactive intermediates. Here, the infrared spectrum of the charge transfer complex [Ar-N2]+, recorded in a supersonic planar plasma with a tunable diode laser spectrometer, is presented. More than 70 adjacent rovibrational transitions were measured near 2272 wave numbers and assigned to the molecular nitrogen stretching fundamental in the 2Sigma+ ground state of [Ar-N2]+. The accurate structural parameters that were determined confirm a linear structure and show that the major part of the charge is located at the argon atom. The latter result is surprising and implies a charge switch of the cationic center upon complexation.     

牡蛎多肽螯合锌的制备及红外光谱分析

以牡蛎酶解多肽液和硫酸锌为原料制备牡蛎多肽螯合锌,应用中心组合试验设计对螯合反应条件进行优化,并对螯合产物进行红外光谱分析和氨基酸含量分析。结果表明:优化后的螯合参数为70.5℃、pH6.94、牡蛎酶解多肽液中氨基酸态氮与锌离子质量比为2.56:1、反应时间为20 min,在此该条件下,锌螯合率为88.25%。液相色谱分析结果表明牡蛎多肽螯合锌中必需氨基酸的百分比含量均基本符合WHO/FAO标准模式谱规定的百分比,红外光谱分析结果则表明螯合产物在2924 cm~(-1)附近有宽吸收峰,说明生成了一种新型的牡蛎多肽锌螯合物,该结果为牡蛎多肽复合产品的生产和开发提供基础性研究数据。     

The infrared spectrum of Al2H6 in solid hydrogen

Although many volatile binary boron hydride compounds are known, binary aluminum hydride chemistry is limited to the polymeric (AlH3)(n) solid. The reaction of laser-ablated aluminum atoms and pure H2 during codeposition at 3.5 kelvin, followed by ultraviolet irradiation and annealing to 6.5 kelvin, allows dimerization of the intermediate AlH3 photolysis product to form Al2H6. The Al2H6 molecule is identified by seven new infrared absorptions that are accurately predicted by quantum chemical calculations for dibridged Al2H6, a molecule that is isostructural with diborane.     

Jupiter: its infrared spectrum from 16 to 40 micrometers

Spectral measurements of the thermal radiation from Jupiter in the band from 16 to 40 micrometers are analyzed under the assumption that pressure-broadened molecular hydrogen transitions are responsible for the bulk of the infrared opacity over most of this spectral interval. Both the vertical pressure-temperature profile and the molecular hydrogen mixing ratio are determined. The derived value ofthe molecular hydrogen mixing ratio, 0.89 +/- 0.11, is consistent with the solar value of 0.86.     

Theory untangles the high-resolution infrared spectrum of the ortho-H2-CO van der Waals complex

Rovibrational spectroscopy of molecules boasts extremely high precision, but its usefulness relies on the assignment of spectral features to corresponding quantum mechanical transitions. In the case of ortho-H(2)-CO, a weakly bound complex abundant in the interstellar medium (although not yet observed there), the rather complex spectrum has been unexplained for more than a decade. We assigned this spectrum by comparison with a purely ab initio calculation. For most lines, agreement to within 0.01 centimeter(-1) between experiment and theory was achieved. Our results show that the applicability of rovibrational spectroscopy can be extended with the assistance of high-accuracy quantum mechanical computations.     

中国6种地带性土壤红外光谱特性研究

利用土壤原样研究了中国 6种典型地带性土壤的红外光谱特征。结果表明 ,砖红壤、红壤红外光谱属于高岭石型图谱 ,显著的 36 95 ,36 2 0 ,10 35 cm- 1峰以及 35 2 7cm- 1峰可作为用红外光谱判断热带、南亚热带地带性土壤的特征峰。黄棕壤、褐土、黑垆土、黄绵土红外光谱为蒙脱石型图谱 ,较弱的 36 2 1cm- 1峰 ,3435和 10 2 8～10 32 cm- 1的强宽带 ,以及显著的 14 37cm- 1峰可作为温带半湿润 -半干旱地区石灰性土壤红外光谱的特征标志。黄棕壤是石灰性土壤向热带、南亚热带地区过渡的地带性土壤 ,其红外光谱标志为较宽的 3435 ,10 32 cm- 1吸收带和明显的 36 2 0 cm- 1吸收峰 ,以及较弱的 36 95 cm- 1峰 ,但没有 14 37cm- 1峰。中国从南到北 ,土壤红外光谱的36 96 ,36 2 1cm- 1 峰、石英双峰 (798,780 cm- 1 )的 797cm- 1 峰吸收强度逐渐减弱 ,而石英双峰的 780 cm- 1 峰吸收强度逐渐增强。     

基于连续投影算法-遗传算法-BP神经网络的可见/近红外光谱木材识别

  目的  基于可见/近红外光谱技术,以10种木材为研究对象,探索不同预处理和特征提取方法下BP神经网络识别木材的效果。  方法  利用美国ASD公司生产的LabSpec 5000光谱仪采集10种木材的光谱图,分别进行移动平均法处理、移动平均法+多元散射校正(MSC)、移动平均法＋标准正态变量变换(SNV)、Savitzky-Golay卷积平滑算法(S-G滤波器)、S-G滤波器+MSC和S-G滤波器+SNV的预处理,运用主成分分析法(PCA)、连续投影算法(SPA)、SPA和遗传算法(GA)联合分别进行特征提取,将提取的特征结合BP神经网络进行木材识别试验。  结果  以SPA和GA联合提取光谱特征时,移动平均法+SNV的预处理效果最佳,以吸收峰为起始波段(W_initial=1 445 nm)、吸收峰个数为特征个数(N_tot=9)时,识别率较高,特征个数大部分减少为SPA提取特征值个数的一半左右。BP神经网络的平均识别速度提升明显。10种木材的平均识别率为98.0%,其中7种木材的识别率达到了100.0%。  结论  在移动平均法+SNV的预处理下,SPA和GA联合提取光谱图的特征,既可提高BP神经网络识别木材的正确率,又可提升识别速度。图3表6参23     

松木层孔菌的液化与红外光谱分析

[目的]优化苯酚—硫酸法液化松木层孔菌的工艺参数,分析液化前后松木层孔菌化学官能团变化,揭示其液化机理,为废弃松木层孔菌的高效利用开辟一条新途径.[方法]以松木层孔菌为原料、浓硫酸为催化剂、苯酚为液化剂,考察料液比(原料/苯酚)、液化温度、液化时间和催化剂用量对松木层孔菌液化率的影响,并通过红外光谱对松木层孔菌原料和液化残渣进行分析.[结果]4个因素对松木层孔菌液化率影响排序为料液比>液化时间>催化剂用量>液化温度,优化的液化工艺参数为:料液比1:6、液化温度170℃、液化时间75 min、催化剂用量0.30 g,在此条件下,松木层孔菌液化率为48.64%.液化前后松木层孔菌红外光谱特征峰的形状和吸收位置均发生明显变化,3366 cm-1的活泼氢吸收峰在液化后发生红移,酰胺羰基吸收峰则分别由1697和1657 cm-1移至1701 cm-1,由1554 cm-1移至1612和1512 cm-1.[结论]采用苯酚—硫酸法可有效液化松木层孔菌,松木层孔菌含氮主要成分几丁质发生脱乙酰化反应,液化产物含有大量酚类物质,可进一步用于制备高附加值化工产品,为高等真菌菌渣的综合利用开辟新途径.     

类锂V~(20+)离子的能量和量子亏损

利用全实加关联(FCPC)方法计算了类锂V20+离子的激发态1s2nd(n≤9)的非相对论的电离能;将相对论效应和质量极化效应作为一级微扰,计算了它们对体系能量的修正;利用有效核电荷方法计算了电子的量子电动力学(QED)效应对电离势的贡献.为了得到高精度的理论结果,还考虑了离子实修正和高角动量分波对能量的贡献.在用FCPC方法得到的V20+离子的激发态能量的基础上,以单通道量子亏损理论(QDT)为依据,计算了Rydberg系列的量子数亏损;将得到的量子数亏损作为输入,又实现了对任意高激发态的能量的理论预言.     

基于连续统去除的土壤有机质近红外光谱敏感波段提取研究

土壤是一个复杂的三相集合体,由土壤中不同物质引起的谱带信息重叠现象非常严重,故通过适当的谱图预处理来提取其敏感波段显得尤为重要。本研究将连续统去除方法引入到土壤有机质敏感波段的提取中,分析了当土壤有机质含量变化时其谱图的变化规律,结果表明:采用连续统去除方法可以很好的提取土壤有机质敏感波段,且以提取的敏感波段600nm、900nm和2 210nm为中心,建立的土壤有机质模型可以较准确的预测土壤有机质含量,其所建模型中预测样本均方根误差MSE为0.286,相关系数R为0.979,均优于全波段所建模型中预测样本的均方根误差3.395和相关系数0.861。连续统去除方法可以很好的提取土壤有机质敏感波段,该研究对土壤有机质快速定量测试仪的研制具有重要意义。     

基于可见近红外光谱及增强回归树算法的鸡蛋种类鉴别

利用可见-近红外光谱技术,选取湖北地区同一品种不同饲养环境下的鸡蛋,提取鸡蛋的光谱透射率(500~900nm),利用标准正态变量变换对光谱数据进行预处理,结合竞争性自适应重加权与主成分分析对光谱数据进行二次降维,并将提取的特征信息输入增强回归树算法,建立鸡蛋土洋种类鉴别模型,模型的训练集和测试集判别正确率分别为98.33%和97.00%。结果表明,应用基于可见-近红外光谱及增强回归树方法,针对同一母鸡品种但不同饲料产出的土洋鸡蛋的种类鉴别是可行的。