铷光谱灯的光谱研究

Rb光谱灯是Rb原子频标的重要部件。Rb光谱灯发出的光含有两种成分,一种是对原子跃迁信号有贡献的有效光成分,一种是仅体现为光噪声的无效光成分。尽可能地增强Rb光谱灯有效光成分并抑制无效光成分,对于提高Rb原子频标锁频环路的信噪比从而改善Rb原子频标的频率稳定度具有重要意义。利用单色仪获得了分别充有起辉气体Ar, Kr和Xe的三种常用Rb光谱灯的光谱,分析了三种Rb光谱灯的光谱特性,讨论了如何提高有效光强和抑制无效光强的问题。实验和分析结果表明,Rb光谱灯有效光强与所用起辉气体的种类和灯泡的工作温度密切相关。灯泡工作温度较低时,Xe灯有用光强最大,Kr灯次之,Ar灯最低;当灯泡工作温度较高时,Xe灯有用光强仍最大,Ar灯次之,Kr灯最低。分析还表明,采用合适的光学滤光方法可以有效地滤除Rb光谱灯的无效光成分。     

光谱成像仪快速光谱定标方法研究

光谱定标是确定光谱仪器各通道中心波长的过程,为了获取光谱辐亮度,通常需要对光谱仪器进行辐射定标,将光谱仪器输出的数值,映射为物理量——辐亮度。不同的光谱仪器的光谱响应不同,因此还需要在光谱定标过程中确定各个通道的光谱响应。光谱成像仪可以看成是多个光谱仪组成的,需要对所有点的中心波长和光谱响应进行定标。自第一台成像光谱仪诞生以来,其定标方法逐渐固定,通常需要采用光谱分辨率较光谱成像仪更高的单色仪输出准单色光进行光谱定标,其准单色光的光谱带宽远小于光谱成像仪的光谱响应带宽,可以将准单色光抽象为脉冲函数。根据脉冲函数的特性,改变准单色光的波长,扫描光谱成像仪的响应波长范围,是对光谱响应函数进行间隔采样的过程,通过光谱定标数据可以直接得到光谱成像仪的中心波长和光谱响应函数。随着技术的发展,探测器的灵敏度越来越高,光谱成像仪的分辨率也越来越高,为了完成光谱定标,对光谱定标需要的准单色光提出了更高的要求。然而准单色光的带宽越窄,其能量越低,获取满足信噪比要求的数据需要更长的时间,使定标的效率降低。从光谱定标的目的出发,结合准单色光和光谱成像仪光谱响应近似高斯函数的特点,通过理论分析,提出一种利用宽带定标光进行光谱定标的方法,可以有效减少光谱定标的步骤,提高定标的效率,适用于光谱成像仪的快速定标。该方法用于某星载高光谱成像仪的光谱定标,待标定光谱成像仪采用棱镜分光,具有色散非线性的特点,光谱分辨率在2~18 nm之间变化,同时存在较大的谱线弯曲,导致每个像元的中心波长都不同,需要对每个像元进行光谱定标。为了避免分视场定标导致的相邻视场中心波长不连续现象,将单色仪发出的准单色光的光斑照亮整个狭缝,狭缝和单色仪之间放置柱透镜和毛玻璃,其中柱透镜用于汇聚垂直于狭缝方向的光线,提高能量利用率;毛玻璃用于匀化光照,毛玻璃的存在极大地减弱了进入光谱成像仪的能量,结合提出的方法,增加定标光的带宽,提高能量,最终完成了该光谱成像仪的快速定标,利用汞灯的特征光谱验证该成像光谱仪的光谱定标精度为0.23 nm。     

鼻咽癌光谱诊断系统中的荧光光谱信号处理

利用激光诱导荧光技术开发了用于早期鼻咽癌诊断的自体荧光光谱系统系统由风冷氩离子激光器、自行研制的单色仪和高灵敏度、智能化的信号采集和处理系统组成文中重点讨论了系统中自体荧光光谱信号的处理技术,其中包括荧光光谱信号的分光和检测技术,以及用LabVIEW开发的信号处理和控制平台荧光光谱信号的处理结果表明:系统不仅实现了荧光光谱信号的同步显示,而且极大地提高了信号的信噪比,这为系统的临床应用奠定了的基础.     

基于光谱分类的干涉光谱图像压缩

针对干涉成像光谱仪所成图像的特点,将分类算法运用于干涉图数据压缩.针对单一和复杂两类目标,采用不同的处理方法,得到了较好的压缩效果.     

基于实测端元光谱的多光谱图像光谱模拟研究

地物光谱特性是遥感应用的基础。然而,在基于野外实测端元光谱的遥感应用中,由于测量尺度不同,导致同一地物光谱形态和反射率值存在很大差异,为遥感信息的定量反演带来困难。文章以新疆塔里木盆地北缘渭干河-库车河绿洲为研究区,选取裸土、植被两类地物作为研究对象,首先通过AVNIR-2传感器的光谱响应函数,实现了将野外实测端元光谱拟合为多光谱离散光谱,通过实例数据表明,拟和的多光谱与AVNIR-2像元光谱具有很好的相关性,在此基础上,采用线性算法建立端元光谱与遥感图像像元光谱的转换模型,实现了从实测端元光谱尺度向遥感多光谱像元尺度的定量光谱转换,为遥感定量分析奠定了一定基础。     

高光谱遥感器的光谱定标

高光谱遥感器光谱性能参数的准确定标是高光谱遥感器数据定量应用的基本前提。本文基于单色准直光标定法对高光谱遥感器进行了光谱性能参数定标,通过数据采集软件及数据处理软件对高光谱遥感器光谱性能参数定标数据进行了分析。分析结果显示:定标测试的重复性在1 h内小于0.2 nm,在20 h内小于0.35 nm。光谱定标结果表明:高光谱遥感器的平均光谱分辨率为4.94 nm,且各高光谱遥感器空间维光谱分辨率均小于5 nm,典型谱段的平均带宽均在6 nm左右。     

光谱参数对基于光谱重构的高光谱数据模拟的影响

遥感数据模拟已广泛应用于遥感研究中, 遥感模拟对于新型传感器的设计,新算法的检测等都有积极的意义。然而传感器系统参数的变化会影响数据模拟的精度。实验采用卷积宽视场多光谱成像仪蓝、绿、红和近红外四个波段的光谱响应函数,基于光谱重构的方法对多光谱数据进行了高光谱的数据模拟。研究分析了多光谱数据中心波长和带宽的变化对高光谱重构精度的影响。结果表明,中心波长和带宽的变化对于光谱重构精度有一定的影响,但总体来说模拟结果有很好的精度。中心波长的变化所引起的RMSE小于0.025,带宽变化引起的RMSE小于0.012。因而基于中心波长和带宽变化的高光谱数据重构有助于用户更好的了解高光谱成像系统,找到系统性能的主要影响者,以便更好的模拟高光谱数据,扩展遥感数据的应用范围。     

基于多光谱成像的光谱反射率重建

一些对颜色重现要求较高的应用领域需要获取目标表面上各点的光谱反射率。大多数天然物质表面的光谱反射率曲线比较平滑,可视为几个基向量的线性组合。基于这一原理的多光谱成像技术可以准确快速地重建目标表面的光谱反射率。通过对NCS色卡进行主成分分析,得出了彩色印刷品光谱反射率的基向量。建立了一个多光谱成像系统,用以比较基向量个数不同对反射率重建效果的影响。     

高光谱图像中纯光谱提取方法

利用线性解混合方法处理高光谱图像数据,需要获取存在于光谱图像中的纯光谱.目前的纯光谱提取方法都需要复杂的运算,并且都没有被证明具有普遍适用的特点,在特征空间对光谱图像中信息存在形式进行有效分析的基础上,提出基于特征空间分析和光谱相关制图法相结合的纯光谱提取方法(FSASCM),具有复杂度低、对大多数高光谱图像数据普遍适用的特点,     

The keto-enol equilibrium in substituted acetaldehydes: focal-point analysis and ab initio limit

High-level ab initio electronic structure calculations up to the CCSD(T) theory level, including extrapolations to the complete basis set (CBS) limit, resulted in high precision energetics of the tautomeric equilibrium in 2-substituted acetaldehydes (XH₂C-CHO). The CCSD(T)/CBS relative energies of the tautomers were estimated using CCSD(T)/aug-cc-pVTZ, MP3/aug-cc-pVQZ, and MP2/aug-cc-pV5Z calculations with MP2/aug-cc-pVTZ geometries. The relative enol (XHC?=?CHOH) stabilities (ΔE _{e,CCSD(T)/CBS}) were found to be 5.98?±?0.17, ?1.67?±?0.82, 7.64?±?0.21, 8.39?±?0.31, 2.82?±?0.52, 10.27?±?0.39, 9.12?±?0.18, 5.47?±?0.53, 7.50?±?0.43, 10.12?±?0.51, 8.49?±?0.33, and 6.19?±?0.18?kcal?mol^?1 for X?=?BeH, BH₂, CH₃, Cl, CN, F, H, NC, NH₂, OCH₃, OH, and SH, respectively. Inconsistencies between the results of complex/composite energy computations methods Gn/CBS (G2, G3, CBS-4M, and CBS-QB3) and high-level ab initio methods (CCSD(T)/CBS and MP2/CBS) were found. DFT/aug-cc-pVTZ results with B3LYP, PBE0 (PBE1PBE), TPSS, and BMK density functionals were close to the CCSD(T)/CBS levels (MAD?=?1.04?kcal?mol^?1).     

A new four-dimensional ab initio potential energy surface and predicted infrared spectra for the Ne–CS2 complex

A new four-dimensional (4D) ab initio potential energy surface (PES) for Ne–CS₂ involving the Q₁ and Q₃ normal modes for the ν₁ symmetric stretching vibration and ν₃ antisymmetric stretching vibration of CS₂ is presented. The PES is constructed at the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)]-F12 level with a large basis set including midpoint bond functions. Two vibrationally averaged potentials with CS₂ at the vibrational ground and ν₁ + ν₃ excited states are generated from the 4D potential. Each potential contains a T-shaped global minimum and two equivalent linear local minima. The rovibrational energy levels and bound states are calculated employing radial discrete variable representation/angular finite basis representation and the Lanczos algorithm. In addition, the predicted band origin shift is 0.2514 cm^?1 for Ne–CS₂. The spectroscopic parameters are also predicted.     

Theoretical rovibrational spectroscopy beyond fc-CCSD(T): the cation CNC+

An accurate near-equilibrium potential energy surface (PES) for CNC⁺ is constructed based on a high-level composite ab initio method. By combining explicitly correlated all-electron CCSD(T)-F12b with scalar relativistic effects and higher order correlation up to coupled cluster theory with singles, doubles, triples and quadruples (CCSDTQ) we achieve convergence in the wavenumbers of the fundamentals to ca. 1 cm^?1. Rovibrational energies are calculated in a variational approach and vibrational term energies and rotational constants are in excellent agreement with available experimental data. Accurate values for centrifugal distortion constants of CNC⁺ in different vibrational states are predicted. Especially the centrifugal distortion constants in the vibrational ground state of D₀ = 0.563 · 10^?6 cm^?1 and H₀ = 0.188 · 10^?10 cm^?1 should be superior to experimentally derived values. Reassignments of some experimentally observed transitions are suggested based on a comparison of experimental and calculated term differences. The bending part of the PES appears to be almost quartic and the band origin of the bending vibration is predicted at 94.2 cm^?1. Absolute line intensities are calculated for various transitions in CNC⁺. For the bending vibration, an intensity is predicted that is three orders of magnitude smaller than for the antisymmetric stretching vibration.     

Ground state rotational spectrum,K = 3 splittings,ab initio anharmonic force field and equilibrium structure of trifluoroamine

The submillimetre-wave spectrum of ¹⁴NF₃ has been measured and the ground state rotational spectrum has been reanalysed, including the K=3 splittings. The quadratic, cubic and semidiagonal quartic force field has been calculated at the CCSD(T) level of theory employing a basis set of at least polarized valence triple-zeta quality. This force field has been used to predict the spectroscopic constants, including the parameters specific to the doubly degenerate vibrational states. The calculated values are found to be in good agreement with the available experimental data. The equilibrium structure has been derived from the experimental ground state rotational constants and either the ab initio or the experimental rovibrational interaction parameters. These experimental and semiexperimental structures are in excellent agreement with the ab initio equilibrium geometry.     

Theoretical studies of three-dimensional potential energy surfaces using neural networks and rotational spectra of the Ar–N2 complex

ABSTRACT

A new three-dimensional potential energy surface (PES) of the Ar–N₂ van der Waals complex is constructed using the neural network method based on ab initio data points at the CCSD(T) level. The aug-cc-pVQZ basis set is employed for all atoms with midbond functions. The vibrationally averaged PES V₀₀ is characterised by a global T-shaped minimum which occurs at R = 3.715 Å, θ = 90.0° with a well depth of 98.779 cm^?1. Based on our three-dimensional PES, bound-state calculations are performed for three isotopomers of Ar–¹⁴N₂, Ar–¹⁵N₂, and Ar–¹⁴N¹⁵N, and several intermolecular vibrational states are assigned by analysing the wavefunctions. Moreover, the averaged structural parameters are calculated and the pure rotational transition frequencies with J = 0--6 are predicted. The spectroscopic constants are determined by fitting the rotational energy levels. The theoretical results are in good agreement with experimental data and this work gives more accurate results than those determined previously for the Ar–N₂ complex.     

The electron affinity of Al13H cluster: high level ab initio study

Al₁₃H clusters have been considered candidates for cluster assembled materials. Here we have carried out benchmark calculations for the Al₁₃H cluster, both neutral and anionic, with the aim of verifying the nature of stationary points on the potential energy surface, studying dynamics of H atom and determining an adiabatic electron affinity. A range of correlated methods applied include second-order perturbation theory (MP2), spin-component-scaled MP2, coupled electron pair (CEPA) and coupled cluster singles and doubles with perturbative triple corrections (CCSD(T)). These methods are used in combination with the correlation consistent basis sets through aug-cc-pVTZ including extrapolation to the complete basis set (CBS) limit. Performance of several different flavours of density functional theory (DFT) such as generalised gradient approximation (GGA), hybrid GGA, meta-GGA and hybrid-meta-GGA is assessed with respect to the ab initio correlated reference data. The harmonic force constant analysis is systematically performed with the MP2 and DFT methods. The MP2 results show that for neutral Al₁₃H only the hollow structure is a potential energy minimum, with the bridged structure being a transition state for the H shift from the hollow site to the adjacent hollow site. The CCSD(T)/aug-cc-pVTZ (CCSD(T)/CBS) estimate of the energy barrier to this H shift is 2.6 (2.9) kcal/mol, implying that the H atom movement over the Al₁₃H cluster surface is facile. By contrast, the DFT force constant analysis results suggest additional terminal and bridged minima structures. For the anion Al₁₃H^?, exhibiting ‘stiffer’ potential energy surface compared to the neutral, the existence of the hollow and terminal isomers is consistent with the earlier photoelectron spectroscopy assignment. The adiabatic electron affinity of Al₁₃H is determined to be 2.00 and 1.95 eV (the latter including the ΔZPE correction) based on the CCSD(T) energies extrapolated to the CBS limit, whereas the respective CCSD(T)/CBS thermodynamic EA values are 2.79 and 2.80 eV.     

An ab initio study of the Ne-CO complex

A new ab initio potential energy surface of the Ne-CO complex is developed using single and double excitation coupled-cluster theory with noniterative treatment of triple excitations [CCSD(T)].The potential has a minimum value of 49.396 cm 1 at R e = 6.40a 0 with approximately T-shaped geometry(θ e = 82.5).Bound state energies are calculated up to J = 12.The theoretically predicted transition frequencies and spectroscopic constants are in good agreement with the available experimental results.     

Rovibrational states of H+ 3. Part 1: The energy region below 9000 cm−1 and modelling of the non-adiabatic effects

This group's variational method for computing rovibrational energies using hyperspherical coordinates and harmonics has been applied to all H⁺ ₃ states below 13000 cm^?1 (J ≤ 10) for which accurate energies based on a submicrohartre accuracy potential energy surface have been obtained. A comparison with a recent comprehensive compilation of experimental data below 9000 cm^?1 shows deviations of up to 1.2 cm^?1. First it is shown that these deviations exert a systematic influence on the vibrational band but depend to a much lesser extent on rotational excitation. Then the remaining discrepancies can be attributed to the neglect of non-adiabatic effects, for which a useful correction formula based on ab initio results is obtained. The scatter in individual bands can thus be reduced to ~0.1 cm^?1 such that these corrected results are consistent with the accuracy of the potential energy surface itself.     

A theoretical-spectroscopy, ab initio-based study of the electronic ground state of SbH3

For the stibine isotopologue , we report improved theoretical calculations of the vibrational energies below 8000 cm⁻¹ and simulations of the rovibrational spectrum in the 0-8000 cm⁻¹ region. The calculations are based on a refined ab initio potential energy surface and on a new dipole moment surface obtained at the coupled cluster CCSD(T) level. The theoretical results are compared with the available experimental data in order to validate the ab initio surfaces and the TROVE computational method [Yurchenko SN, Thiel W, Jensen P. J Mol Spectrosc 2007;245:126-40] for calculating rovibrational energies and simulating rovibrational spectra of arbitrary molecules in isolated electronic states. A number of predicted vibrational energies of are provided in order to stimulate new experimental investigations of stibine. The local-mode character of the vibrations in stibine is demonstrated through an analysis of the results in terms of local-mode theory.     

Profiling the binding motif between Be and Mg in the ground state via a single-reference coupled cluster method

We present a study on the performance of our iterative triples correction for the coupled cluster singles and doubles excitations (CCSDT-1a+d) method for computation of potential energy surface (PES), spectroscopic constants, and vibrational spectrum for the ground state (X¹Σ⁺) BeMg, where the ostensible inadequacy of the CCSD and CCSD(T) methods is quite expected. We compare our results with those obtained using state-of-the-art multireference configuration interaction (MRCI) investigations reported earlier by Kerkines and Nicolaides. Our estimated dissociation energy (417.37 cm^?1), equilibrium distance (3.285 Å), and vibrational frequency (82.32 cm^?1) are in good agreement with recent results of advanced MRCI calculations for X¹Σ⁺ BeMg PES, which exhibits a shallow well of 469.4 cm^?1 with a minimum at 3.241 Å and a harmonic vibrational frequency of 85.7 cm^?1. Very weakly bound nature of X¹Σ⁺ BeMg is clearly reflected from these values. In accord with MRCI studies, a comparison of BeMg with iso-valence weakly bound ground-state species, Be₂ and Mg₂, suggests that its characteristics do not exhibit any resemblance to Be₂ rather, it shows a close kinship to Mg₂. The agreement of our derived vibrational levels with those obtained via the high-level MRCI calculations is very encouraging reflecting the potential of the suitably modified single-reference coupled cluster (SRCC) method, CCSDT-1a+d as a tool for the study of multireference van der Waals systems.