Calculated potential surfaces for the description of the emission spectrum of the C2H radical

Ab initio MRD-CI calculations are reported for the CC stretch and CCH bending potential surfaces for the lowest-lying electronic states of the ethynyl radical. It is found that the energies of the fully relaxed $\text{π → π}{}^1$ states of this system are as much as 2.3 eV below the corresponding values at the ²Σ⁺ ground state (linear) equilibrium structure. The fact that the energy minima for the C₂H excited states occur for widely different internuclear arrangements than that of the ground state is shown to be very consistent with the experimental observation that the electronic spectrum of C₂H has a much different appearance in emission than it does in absorption studies. On the basis of both calculated energy differences and oscillator strength results it is found that the most likely assignment for the broad emission feature in the 4000–6000 Å region of the C₂H spectrum is caused by vertical excitation from the lowest vibrational levels of the 3²A′ (and also 2²A″) upper states to the 2²A′, ²A′ and ²A″ species which correlate with X²Σ⁺ and A²Π for linear nuclear arrangements; the possible mechanisms for production of 3²A′ and 2²A″ upon photolysis of acetylene are also discussed. The possibility that spinforbidden transitions are involved at longer wavelengths in this spectral region is also considered. Finally it is pointed out that a potential crossing of the linear $\text{X}\text{?}{}^2\text{Σ}{}^{\mathrm{+}}$ and A²Π species calculated to occur in the neighborhood of R_CC = 2.6 bohr, which becomes sharply avoided upon molecular bending, would be expected to lead to the type of irregular vibronic structure in the 3600 cm^?1 region of the C₂H IR spectrum recently observed by Jacox.     

Ultraviolet absorption spectrum and cross-sections of ethynyl (C2H) radicals

This work reports the ultraviolet absorption spectrum and cross-sections of ethynyl (C₂H) radicals in the wavelength range 235-260 nm, determined at T=298 K and at a total pressure of about 20 kPa (150 Torr). Ethynyl radicals were produced from the single photon 193 nm excimer laser photolysis of dilute mixtures of C₂HCF₃ or C₂H₂ in He. Gas chromatographic/mass spectroscopic analysis of the photolyzed samples showed diacetylene (C₄H₂) as the major stable product. Addition of methane in the photolysis mixtures resulted in reduction of diacetylene and production of methylacetylene and ethane, products of the reaction of ethynyl radicals with methane. Survey of the ultraviolet spectral region, employing time-resolved UV-absorption spectroscopy, resulted in detection of a transient absorption centered at about 243 nm. The spectra obtained from the 193-nm photolysis of both C₂HCF₃/He and C₂H₂/He radical precursors were nearly identical, suggesting that the absorption feature can be attributed to the ethynyl radicals. The observed ultraviolet spectrum exhibits a relatively broad absorption feature with some structures and an absorption peak at about 243.5 nm. The absorption cross-sections for ethynyl radicals have been determined in this work for the first time. The C₂H cross-section, at the maximum absorption, at 243.5 nm is . The stated uncertainty includes the random and systematic measurement errors. The UV absorption feature, detected in this work, can be assigned to the transitions from the ground electronic state and also possibly from coupled ground and lowest electronic states to the electronic state B (or 32A′) of C₂H. This assignment is based on previously reported high level ab initio molecular orbital calculations and results of recent laser-induced fluorescence studies of the ethynyl radical.     

Gas phase electronic spectrum of propadienylidene C3H2

The rotationally resolved vibronic bands in the forbidden electronic transition of the cumulene carbene C₃H₂ have been observed in the gas phase by cavity ring down absorption spectroscopy through a supersonic planar plasma with allene as precursor. The band detected in the 16 223 cm⁻¹ region is a result of vibronic interaction and is assigned to a combination of a₁ and b₂ vibrations with a frequency around 2250 cm⁻¹. Another vibronic band near 15 810 cm⁻¹ has an unusual rotational structure because the K_a = 0-1 subband is absent. It is assigned to a combination of a₁ and b₁ vibrations, ∼1850 cm⁻¹, which borrow intensity from the near lying state due to a-type Coriolis coupling. A rotational analysis using a conventional Hamiltonian for an asymmetric top molecule yields molecular constants for the vibrational excited levels of the ùA₂ state, which were used for the determination of the geometry. The stronger transition of C₃H₂, measured in a neon matrix in the 16 161-24 802 cm⁻¹ range, was not detected. The reason for this is a short lifetime of the state, leading to line broadening.     

乙烯和乙炔基在Ni(110)表面上吸附结构的研究

采用平面波赝势方法，利用基于从头计算的软件包，对乙烯和乙炔基在Ni(110)表面上吸附的问题进行了计算. 在低覆盖度时，孤立的乙烯分子的吸附能比密集时高，乙烯分子的C-C 轴大致沿衬底的Ni原子链方向(即沿［110］晶向)，C-C轴与衬底Ni(110)表面有12°的倾斜角，乙烯分子的C—C键的键长为 0.147nm. 乙烯分子中接近顶位的C原子与衬底中距离最近的Ni原子为0.199nm. 在高覆盖度时，乙烯分子在Ni(110)表面上形成c(2×4)再构，每个表面二维元胞中有两个乙烯分子，每个乙烯分子的吸附位置与低覆盖度时相似，而C—C键长比低覆盖度时要短. 乙炔基是乙烯在Ni(110)表面上分解的产物. 关于乙炔基的计算结果表明：乙炔基的两个C原子的间距为0.131nm，比乙烯分子中C原子的间距更短. 与乙烯分子相比，乙炔基的吸附位置更靠近顶位. H原子与吸附在顶位上的C原子相连接，C—H键也大致沿衬底的Ni原子链方向，与Ni表面呈45°的倾斜角. 关键词： 乙烯和乙炔基 平面波赝势方法 吸附几何结构     

Nb2H 的电子结构和相互作用

应用基于密度泛函理论的赝势-平面波方法研究了Nb₂H的电子结构和H原子占据点之间的关系.计算结果表明：由4个Nb近邻构成的四面体中心点(T点)为H的稳定俘获点，而由6个Nb近邻构成的八面体中心点(O点)则为相互作用势的极大值点，是不稳定点.相邻T点间存在低能量通道，具有鞍点(S点)结构.在T点及近邻低能通道上,H的1s能级展宽较弱，Nb的4d, 5s 带部分向下延展，与H带杂化后形成孤立带.当H由T向     

Optical and ESR spectra of the C4H radical in rare gas matrices at 4 K

C₄H (butadinyl) was trapped in Ar and Ne matrices at 4 K by the uv photolysis of a mixture of C₄H₂ and the rare gas. CC stretching and CH bending modes have been identified in the ir at 2060 and 735 cm^?1. A band system appearing in the 2500–3000 Å region with (0, 0) at 33 800 cm^?1 has been analyzed and tentatively assigned to a ²Π_r ← X²Σ transition. C₄D: Ar spectra confirm the optical assignments. The ESR spectrum exhibits a proton hyperfine splitting b = A_⊥(H) = 16.5 MHz, at g_⊥ = 2.0004(5). The spin-doubling constant, γ, is estimated to be +0.0006(2) cm^?1.     

Sub-millimeter wave spectroscopy of the C3H radical: Ro-vibrational transitions from ground to the lowest bending state

Linear C₃H in its (X²Π) electronic ground state possesses strong Renner-Teller coupling in the two lowest bending modes, ν₄ and ν₅. The ²Σ^μ level of the v₄ = 1 bending mode is shifted towards lower energies and is supposed to lie only 20.3 cm⁻¹ above the ground state [S. Yamamoto, S. Saito, H. Suzuki, S. Deguchi, N. Kaifu, S. Ishikawa, M. Ohishi, Astrophys. J. 348 (1990) 363]. In the present study, first measurements of ro-vibrational transitions from the ²Π_3/2 ground state to the ²Σ^μ lowest vibrational state were performed using a Terahertz spectrometer equipped with a supersonic jet nozzle. Rotational levels of the ²Π_3/2 and v₄ = 1(²Σ^μ) state are close in energy and a crossing of the rotational energy ladders occurs between J = 24.5 and 25.5. A strong vibronic coupling leads to a significant intensity enhancement of ²Π_3/2 − ²Σ^μ ro-vibrational transitions. The search for ro-vibrational transitions was facilitated by measurements on pure rotational transitions in the ²Π_1/2, ²Π_3/2 and v₄ = 1(²Σ^μ) states, substantially extending the former data set published by Yamamoto et al. Data analysis yields an accurate value for the v₄ = 1(²Σ^μ) energy level which has been found to lie 609.9771(42) GHz or 20.34664(14) cm⁻¹ above the ²Π ground state. Furthermore, the value of the vibronic coupling constant β has been improved significantly and determined as 1231.77(51) MHz. The new set of spectroscopic parameters obtained in the present study permits very reliable frequency predictions into the Terahertz region.     

外场作用下C12H4Cl4O2的分子结构和电子光谱研究

各种环境毒物危害着人类的生产生活,二噁英更是严重危害人类的健康.C₁₂H₄Cl₄O₂（2,3,7,8-tetrachlorodibenzo-p-dioxin,TCDD）是二噁英中毒性最强的化合物,也是目前已知毒性最强的污染物.为研究TCDD外场效应,采用密度泛函理论方法优化了不同静电场0–0.025 a.u.（0–1.2856×10¹⁰ V/m）作用下TCDD分子的基态几何结构,得到了分子总能量;在此基础上,采用含时密度泛函理论方法对TCDD分子的紫外-可见（UV-Vis）吸收光谱在不同外电场下的变化进行了研究.结果表明：分子几何构型与电场大小呈现强烈的依赖关系,分子总能量随着外电场的增强而减小;伴随着外电场的增强,分子激发态的摩尔吸收系数逐渐减小,UV-Vis吸收峰显著红移.     

Microwave spectrum of the HO2 radical

Rotational transitions of the HO₂ free radical, a type 1₀₁ ← 0₀₀, 2₀₂ ← 1₀₁, 2₁₂ ← 1₁₁, and 2₁₁ ← 1₁₀, and b type 6₁₆ ← 7₀₇, 7₁₇ ← 8₀₈, 9₀₉ ← 8₁₈, and 10_0,10 ← 9₁₉, have been observed up to 137 GHz with microwave spectroscopy. The rotational constants, the centrifugal distortion constants in the symmetric-top approximation, the spin-rotation coupling constants, and the coupling constants of Fermi contact and dipole-dipole interactions are determined accurately. The absolute value of ?_ab + ?_ba, the off-diagonal component of the spin-rotation interaction tensor, is obtained from its second-order perturbation contributions to the spin doublings of the b-type rotational transitions. The small value of the Fermi contact parameter leads to the conclusion that the hydroperoxyl radical is a π-electron radical. The lowest two K-type doubling transitions, which are of particular interest to radioastronomy, are predicted on the basis of the molecular constants obtained.     

Rotationally resolved electronic spectroscopy of a nonlinear carbon chain radical C6H4

Rotationally resolved electronic spectrum of the origin band in the 2A″-X2A″ transition of a nonlinear carbon chain radical C₆H₄⁺ has been recorded in the 604 nm region using cw cavity ring down spectroscopy. The radical was produced by a discharge through an acetylene-helium mixture in a supersonic planar expansion. The rotational structure has been analysed and precisely determined. A band having a-type prolate rotational structure has also been observed near 581 nm. By considering the results of ab initio calculations this band is assigned to a transition involving the excitation of the ν₁₂ fundamental in the upper 2A″ electronic state of the same C₆H₄⁺ isomer.     

Theoretical electronic transition moments for the Ballik-Ramsay,Fox-Herzberg,and Swan systems OF C2

Potential energy curves and spectroscopic constants T_e, r_e, ω_e, and ω_eχ_e have been calculated for the a³Π_u, b³Σ^-_g, d³Π_g and e³Π_g electronic states of C₂ using self-consistent-field plus configuration-interaction techniques. These results are in excellent agreement with those obtained from experiments. The variation of the electronic transition moment with internuclear separation has been calculated for the Ballik-Ramsay system (b³Σ^-_g-a³Π_u), Fox-Herzberg (e³Π_g-a³Π_u), and Swan (d³Π_g-a³Π_u) band systems. These results are in good agreement with existing experimental and theoretical data.     

The microwave spectrum of the PH2 radical

Three rotational transitions, 1₁₀ ← 1₀₁, 2₂₀ ← 2₁₁, and 3₃₀ ← 3₂₁, of the PH₂ radical in the ground vibronic state were observed in the mm-wave region, by using a source-frequency modulation spectrometer with a 1-m-long free space cell. The PH₂ radical was generated directly in the cell by glow discharge in a mixture of phosphine and oxygen. Thirty four fine and hyperfine components were measured for the three transitions. An analysis of the observed spectra, combined with far-infrared and mid-infrared laser magnetic resonance spectra and laser-induced fluorescence spectra obtained by other works, improved the rotational and spin-rotation interaction constants in precision. The observed hyperfine structure gave the magnetic hyperfine coupling constants for both P and H nuclei and also the P nuclear spin-rotation interaction constants.     

The microwave spectrum of the DO2 radical

The a-type N = 1 ← 0,2 ← 1, and 3 ← 2 and the b-type 1₁₁ ← 2₀₂, 2₁₂ ← 3₀₃, 3₁₃ ← 4₀₄, 6₀₆ ← 5₁₅, and 7₀₇ ← 6₁₆ transitions, 14 in total, of the DO₂ free radical in the ground vibronic state were observed by microwave spectroscopy in the frequency region up to 200 GHz. The DO₂ radical was generated in a free-space absorption cell by a DC discharge in a mixture of CH₃OD and O₂. From the observed spectra the rotational constants, centrifugal distortion constants, spin-rotation coupling constants, and magnetic hyperfine coupling constants were determined with good precision. The hyperfine coupling constants of DO₂ were determined by the present work for the first time. A comparison of the in-plane components of the dipole-dipole interaction tensor of DO₂ with those of HO₂ made it possible to determine the off-diagonal component T_ab, and thus the principal values and the principal axes of the tensor.     

Theoretical study on the vertical electronic spectrum of nitrosyl fluoride (ONF)

Combined self-consistent field and configuration-interaction calculations were carried out on the excited states of nitrosyl fluoride. Results of these calculations confirm the assignment of the electronic transition 1¹A″ ← X¹A′ observed to occur between 3.70 and 4.77 eV, with an absorption maximum at 3.99 eV. A comparative study between the calculated vertical spectra of HNO and ONF is made.     

A comparative MRD-CI study of the electronic spectrum of linear and cyclic C8 clusters

Multi-reference configuration interaction MRD-CI calculations are performed to compute the vertical electronic spectrum of linear and cyclic C₈⁺ clusters. The electronic spectrum of the linear C₈⁺ isomer is dominated by the transition computed at 5.45 eV. The first dipole-allowed transition of linear C₈⁺ () is calculated at 1.69 eV, whereas several transitions are calculated with medium oscillator strengths between 2.30 and 5.14 eV. For the cyclic C₈⁺ form we computed important transitions at 1.83 and 4.20 eV. In addition, the first dipole-allowed transition of cyclic isomer is computed at 0.77 eV (). This transition should help to identify the cyclic C₈⁺ species since there are no dipole-allowed transitions of the linear isomer in this energy region.     

Energy spectrum of C60 fullerene

The energy spectrum of the C₆₀ fullerene has been calculated in terms of the Shubin-Vonsovskii-Hubbard model using an approximation of static fluctuations. Based on the spectrum, the optical absorption bands at 4.84, 5.88, and 6.30 eV observed experimentally have been successfully explained. It has been concluded that the model used is applicable for the calculation of the energy spectrum and the energy properties of other nanosystems, such as fullerenes of higher orders, carbon nanotubes, and grafen planes.     

10－5000 伏下电子被多原子分子CF4, CF3H, C2F4, C2F6, 及 C2H3F3散射总结面的计算

利用可加性规则和光学势方法计算了能量在10-5000 eV范围内电子被多原子分子CF4, CF3H, C2F4, C2F6, 及 C2H3F3的总结面，并与已有的实验结果和理论计算进行了比较，与这些结果符合得很好。对于CF4, CF3H, C2F4, C2F6, 及 C2H3F3在1000eV以上没有实验数据，本文对实验研究提供了对比和预测的数据。     

Laser-excited phosphorescence spectrum of C3S2 in an Ar matrix

The phosphorescence spectrum of C₃S₂ was observed in a low-temperature Ar matrix with excitation of an Ar⁺ laser. The spectrum consists of a very strong 0-0 band at 18 287 cm^?1 and well-resolved progressions in the ν₂, ν₅, ν₆, and ν₇ vibrations. Side bands were found on the high-energy sides of some transitions. The separation between the main and side bands is 23 cm^?1. Polarization analysis suggests that C₃S₂ is linear symmetric in the Phosphorescent state as in the ground electronic state. On the basis of symmetry considerations and a qualitative evaluation of spin-orbit coupling, the phosphorescent state is assigned to ³Σ_u^? with Σ_u⁺ and Π_u components split by spin-spin interaction. The Σ_u⁺ level is lower than the Π_u one by 23 cm^?1 and the main and side band emissions start from the Σ_u⁺ and Π_u levels, respectively. The Σ_u⁺ component seems to acquire allowed character from a ¹Σ_u⁺ state by spin-orbit coupling and from bent ${}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{?}}\text{(}{}^1\text{B}{}_2\text{)}$ and ${}^1\text{Δ}{}_{\mathrm{g}}\text{(}{}^1\text{A}{}_1\text{+}{}^1\text{B}{}_2\text{)}$ states by ν₅ vibronic coupling. Mixing of the Σ_u⁺ and Π_u components through ν₅ is responsible for most of the side bands. The ν₅ frequency is estimated to be 160 ± 20 cm^?1 in the ³Σ_u^? state from the intensities of ν₅ progression bands and from the ground-state frequency, 411 cm^?1.     

C72,La2@C72几何结构和电子性质的计算研究

采用密度泛涵理论(density functional theory, DFT)中的广义梯度近似(generally gradient approximation, GGA)对富勒烯C₇₂和内掺金属La富勒烯La₂@C₇₂三种同分异构体的几何结构和电子结构进行研究.发现在C₇₂的三种同分异构体中，满足独立五边形规则(isolated-pentagon-rule，IPR)的C₇₂(D_{6d< 关键词： 72}')" href="#">C₇₂ 2@C₇₂')" href="#">La₂@C₇₂ 密度泛涵理论 几何结构 电子结构