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.     

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.     

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.     

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+.     

The rotational spectrum of the water-hydroperoxy radical (H2O-HO2) complex

Peroxy radicals and their derivatives are elusive but important intermediates in a wide range of oxidation processes. We observed pure rotational transitions of the water-hydroperoxy radical complex, H2O-HO2, in a supersonic jet by means of a Fourier transform microwave spectrometer combined with a double-resonance technique. The observed rotational transitions were found to split into two components because of the internal rotation of the water moiety. The molecular constants for the two components were determined precisely, supporting a molecular structure in which HO2 acts as a proton donor to form a nearly planar five-membered ring, and one hydrogen atom of water sticks out from the ring plane. The structure and the spectral splittings due to internal rotation provide information on the nature of the bonding interaction between open- and closed-shell species, and they also provide accurate transition frequencies that are applicable to remote sensing of this complex, which may elucidate its potential roles in atmospheric and combustion chemistry.     

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 deconstruction of the infrared spectrum of CH5+

We present two quantum calculations of the infrared spectrum of protonated methane (CH5+) using full-dimensional, ab initio-based potential energy and dipole moment surfaces. The calculated spectra compare well with a low-resolution experimental spectrum except below 1000 cm(-1), where the experimental spectrum shows no absorption. The present calculations find substantial absorption features below 1000 cm(-1), in qualitative agreement with earlier classical calculations of the spectrum. The major spectral bands are analyzed in terms of the molecular motions. Of particular interest is an intense feature at 200 cm(-1), which is due to an isomerization mode that connects two equivalent minima. Very recent high-resolution jet-cooled spectra in the CH stretch region (2825 to 3050 cm(-1)) are also reported, and assignments of the band origins are made, based on the present quantum calculations.     

Dynamics affecting the primary charge transfer in photosynthesis

Analysis of a 60-picosecond molecular dynamics trajectory of the reaction center of Rhodopseudomonas viridis provides an understanding of observations concerning vibrational coherence and the nonexponential kinetics of the primary charge transfer in photosynthesis. Complex kinetics arises from energy gap correlations that persist beyond 1 picosecond.     

基于DNA双链电荷转移的Hg2+电化学生物传感器的研究

基于DNA双链电荷转移原理,利用胸腺嘧啶(thymine)与Hg2的特异性识别和计时电量法构建了一种高灵敏检测水溶液中Hg2的电化学生物传感器.该传感器将含有1个T-T碱基错配对的DNA互补双链通过Au-S键自组装在金电极表面,运用计时电量法在含有亚甲基蓝的铁氰化钾溶液中进行测定.T-T错配阻断了DNA双链内部电荷转移,而Hg2通过T-Hg2-T配位作用与双链DNA特异性结合并形成DNA双链内部电荷转移通路,引起电极表面计时电量的变化.计时电量测定结果显示:在亚甲基蓝的还原峰电位(-380mV)附近,计时电量随着溶液中的Hg2+浓度的增大而增加,Hg2+浓度在1.0 nmol/L～ 104 nmol/L范围内,计时电量的变化量与Hg2浓度的对数呈良好的线性关系,线性相关系数(R2)为0.997,检测限为0.5 nmol/L(S/N=3).干扰实验表明,该传感器对Hg2具有良好的特异性和选择性.     

基于DNA双链电荷转移的Hg2+电化学生物传感器的研究

基于DNA双链电荷转移原理,利用胸腺嘧啶(thymine)与Hg~(2+)的特异性识别和计时电量法构建了一种高灵敏检测水溶液中Hg~(2+)的电化学生物传感器。该传感器将含有1个T-T碱基错配对的DNA互补双链通过Au-S键自组装在金电极表面,运用计时电量法在含有亚甲基蓝的铁氰化钾溶液中进行测定。T-T错配阻断了DNA双链内部电荷转移,而Hg~(2+)通过T-Hg~(2+)-T配位作用与双链DNA特异性结合并形成DNA双链内部电荷转移通路,引起电极表面计时电量的变化。计时电量测定结果显示:在亚甲基蓝的还原峰电位(-380m V)附近,计时电量随着溶液中的Hg~(2+)浓度的增大而增加,Hg~(2+)浓度在1.0 nmol/L~104nmol/L范围内,计时电量的变化量与Hg~(2+)浓度的对数呈良好的线性关系,线性相关系数(R2)为0.997,检测限为0.5 nmol/L(S/N=3)。干扰实验表明,该传感器对Hg~(2+)具有良好的特异性和选择性。     

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。     

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.     

Nondestructive measurement of internal quality of Nanfeng mandarin fruit by charge coupled device near infrared spectroscopy

The soluble solids content (SSC) and total acidity (TA) are the major characteristics for assessing quality and maturity of Nanfeng mandarin fruits. The feasibility of charge coupled device near infrared spectroscopy (CCD-NIRS) combining with effective wavelengths selection algorithm used to measure SSC and TA nondestructively was investigated. The effective wavelengths to SSC and TA were chosen by interval partial least squares (iPLS) in the wavelength range of 600–980 nm. The predictive ability of SSC model used PLS regression was improved with r of 0.92 and RMSEP of 0.65 °Brix using effective wavelengths of 681.36–740.51 nm, 798.60–836.19 nm and 945.52–962.75 nm. The TA model was simplified with r of 0.64 and RMSEP of 0.09% using effective wavelengths of 817.57–836.19 nm, 909.85–927.60 nm and 945.52–962.75 nm. The experimental results demonstrated that the CCD-NIRS technique combining with iPLS algorithm was a feasible method to measure SSC and TA of Nanfeng mandarin fruits nondestructively.     

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。     

Effect of infrared transparency on the heat transfer through windows: a clarification of the greenhouse effect

The various radiative, convective, and conductive components of the net heat transfer are calculated and illustrated for various infrared transparencies of covers such as would be used in architectural, greenhouse, or solar collector windows. It is shown that in the limiting cases of infrared opacity and infrared transparency the relative contributions of the three modes of heat transfer are altered, but all contribute significantly. The radiation shielding arguments pertain to the analogous green-house effect in the atmosphere.     

电荷转移光谱法分析植物材料中的胆碱

作者研究了孔雀绿－胆碱磷钼杂多酸－ＰＶＡ体系，提出了一种相对简便、灵敏测定植物材料中痕量总胆碱的方法．方法的线性范围为０．５～２００ｎｍｏｌ／Ｌ，回收率大于８５％．     

3种颜色玉米胚乳胚芽的FTIR结合聚类分析研究

[目的]研究玉米胚乳胚芽的傅里叶变换红外光谱,为鉴别不同种类玉米提供科学手段.[方法]利用傅里叶变换红外光谱技术,结合系统聚类分析对3种类型的玉米实体样本的胚乳胚芽进行研究.[结果]原始红外光谱700～1 800 cm-1总体特征相似,主要是由多糖、蛋白质、脂类等吸收谱峰组成,在此范围内3种样本的原始光谱存在微的差异.对光谱进行一阶导数和二阶导数处理,用二阶导数光谱进行系统聚类分析（HCA）,结果表明二阶导数光谱700 ～1 800 cm-1范围按玉米胚芽和胚乳样本聚类效果较好,52个样本能按3个种类很好地聚类,分类正确率达96.1％.[结论]红外光谱结合系统聚类分析方法可用于鉴别不同种玉米胚乳胚芽,具有方便、快速的优点.     

基于遗传多层前馈神经网络的大豆脂肪酸含量近红外光谱检测

文章提出了一种利用遗传多层前馈神经网络建立数学模型的方法,建立起化学测定值与近红外光谱数据之间的定量关系。把得到的近红外光谱数据作为网络的输入,把用化学法测定的5种脂肪酸含量作为网络的输出,再利用遗传算法训练多层前馈神经网络的权值,建立大豆脂肪酸的神经网络检测模型,探索出一种能够准确、高效地完成近红外光谱检测的神经网络模型,文中设计了一种用遗传算法训练的多层前馈神经网络。通过试验证明,用遗传算法优化人工神经网络的权重,获得高于单纯用人工神经网络训练的结果。大豆5种脂肪酸的相关系数都可达到0.9左右,能够满足大豆育种的初步检测。