Lowest Π–Π* electronic transitions in linear and two-dimensional polycyclic aromatic hydrocarbons: enhanced electron density edge effect

Polycyclic aromatic hydrocarbons (PAHs) form an important class of molecules as they are ubiquitous, pollute air and cause severe health problems. Lowest vertical π–π* singlet–singlet or triplet–triplet excitation energies and corresponding oscillator strengths were studied for several linear and two-dimensional PAHs employing time-dependent density functional theory. Excited-state electron density, molecular electrostatic potential (MEP) and spin density distributions in the PAHs, along with ground-state chemical hardness, were also studied. It has been found that, generally, excitation energies and oscillator strengths decrease with increase in PAH size, and excitation energies and chemical hardness are strongly linearly correlated. Enhanced electron density edge effect, which was found to occur in the ground states of the molecules, continues to hold in their excited states also. A strong similarity between the ground and π–π* excited-state MEP maps suggests that σ electrons are the main contributors to the enhanced electron density at the edges. Due to their strong electronic absorption transitions in the visible and infrared regions, the PAHs can be used for harnessing solar energy efficiently.     

不同Yb掺杂量的Yb:Y3Al5O12晶体的光谱分析

采用提拉法生长了Yb³⁺掺杂量分别为5.4at%, 16.3at%, 27.1at%, 53.6at%和100at%的Yb:Y₃Al₅O₁₂晶体.系统地表征和分析了Yb³⁺掺杂量对晶体吸收光谱和荧光光谱的影响.随着Yb³⁺掺杂量的增加，各峰值吸收系数呈线性增加的趋势.应用Smakula公式计算了各吸收峰对应的振荡强度，并分析了Yb³⁺掺杂量对振荡强度的影 关键词： 吸收光谱 荧光光谱 自吸收 浓度猝灭     

Chiroptical spectra of molecules with nearly degenerate electronic states

The influence of vibronic interactions on the chiroptical spectra associated with pairs of nearly degenerate electronic transitions in chiral systems is examined on a formal theoretical model. We consider the special case in which two nearly degenerate electronic states are coupled by a single non-totally symmetric vibrational mode. Formal expressions are developed for the rotatory strengths of individual vibronic transitions in this coupled system. Calculations based on these expressions are carried out for a large number of parameter sets appropriate for various energy spacings between the unperturbed electronic states, vibronic coupling strengths, oscillator (vibrational mode) frequencies, and electronic rotatory strengths. The calculated results demonstrate the profound influence of vibronic interactions on the sign patterns and intensity distributions within the rotatory strength spectrum associated with the two coupled electronic states. The implications of these results for interpretations of circular dichroism spectra are discussed.     

V+20离子的能量和偶极振子强度

用全实加关联方法计算了类锂V+20离子 1s2nl(l=s,p, d;n≤9) 态的电离势和精细结构.依据单通道量子亏损理论, 确定了这三个Rydberg系列的量子数亏损.用这些作为能量的缓变函数的量子亏损,可以实现对任意高激发态(n≥10)的能量的可靠预言.用在计算能量过程中确定的波函数,计算了V+20离子1s22s-1s2np及1s22p-1s2nd (n≤9)跃迁的振子强度.将这些分立态振子强度与单通道量子亏损理论相结合,得到在电离域附近束缚态间的偶极跃迁振子强度以及束缚态-连续态跃迁的振子强度密度,从而将V+20离子的这一重要光谱特性的理论预言外推到整个能域.     

Mn22+离子1s22s-1s2np的偶极跃迁能和振子强度

用全实加关联方法计算了类锂Mn22 离子1s22s-1s2np(2≤n≤9)的偶极跃迁能和振子强度.1s2np(2≤n≤9)态的精细结构通过计算自旋-轨道与自旋-其他轨道相互作用算符的期待值确定.依据单通道量子亏损理论,确定了Rydberg系列1s2np的量子数亏损.从而可以用这些作为能量的缓变函数的量子亏损,实现对任意高激发态(n≥10)的能量的可靠预言.将这些分立态振子强度与单通道量子亏损理论相结合,得到在电离阈附近束缚态-束缚态跃迁振子强度以及束缚态-连续态跃迁的振子强度密度,从而将Mn22 离子的这一重要光谱特性的理论预言外推到整个能域.     

Oscillator strengths for 2 ^2P-n ^2D transitions of lithium-like systems with Z=11 to 20

The dipole-length, velocity and acceleration absorption oscillator strengths for the 1s^22p－1s^2nd(3≤n≤9) transitions of the lithium-like systems with Z=11 to 20 are calculated using the energies and the multiconfiguration interaction wavefunctions obtained from a full core plus correlation method. The agreement between the f-values calculated from the length, velocity and acceleration formulae is excellent. Our results agree closely with the experimental data available in the literature. Combining these discrete oscillator strengths with the single-channel quantum defect theory, the discrete oscillator strengths for the transitions from 1s^22p state to highly excited states (n≥10) and the oscillator strength densities corresponding to the bound-free transitions are obtained.     

Sc+18离子1s23d-1s2nf的跃迁能和偶极振子强度

用全实加关联方法计算了类锂Sc 18离子1s23d-1s2nf(4≤n≤9)的跃迁能和1s2nf(n≤9)态的精细结构。依据量子亏损理论确定了该Rydberg系列的量子数亏损,用这些作为能量的缓变函数的量子亏损,可以实现对任意高激发态(n≥10)的能量可靠的预言。利用在计算能量过程中确定的波函数,计算了Sc 18离子1s23d-1s2nf的偶极跃迁在三种规范下振子强度;将这些分立态振子强度与量子亏损理论相结合,得到在电离阈附近束缚态-束缚态跃迁振子强度以及束缚态-连续态跃迁振子强度密度,从而将Sc 18离子的这一重要光谱特性的理论预言外推到整个能域。     

Cr~(21+)离子1s~23d-1s~2nf的跃迁能和偶极振子强度(英文)

用全实加关联方法计算了类锂Cr21+离子1s23d-1s2nf(4≤n≤9)的跃迁能和1s2nf(n≤9)态的精细结构.在类氢近似下估算了对能量的高阶相对论修正.依据量子亏损理论,确定了Rydberg系列1s2nf的量子数亏损.据此可以实现对任意高激发态(n≥10)的能量的可靠预言.计算了Cr21+离子1s23d-1s2nf(4≤n≤9)跃迁的振子强度.与量子亏损理论相结合,得到该离子从1s23d态到电离阈附近高激发束缚态间的偶极跃迁振子强度以及到相应连续态跃迁的振子强度密度,从而将Cr21+离子的这一重     

Computation of the oscillator strength and absorption coefficients for the intersubband transitions of the spherical quantum dot

The electronic structure and optical properties of one-electron Quantum Dot (QD) with and without an on-center impurity were investigated by assuming a spherically symmetric confining potential of finite depth. The energy eigenvalues and the state functions of QD were calculated by using a combination of Quantum Genetic Algorithm (QGA) and Hartree–Fock Roothan (HFR) method. We have calculated the binding energy for the states 1s,1p,1d,1f, oscillator strengths, the linear and third-order nonlinear optical absorption coefficients as a function of the incident photon energy and incident optical intensity for the 1s–1p, 1p–1d and 1d–1f transitions. The existence of the impurity has great influence on the optical absorption spectra and the oscillator strengths. Also we found that the magnitudes of the total absorption coefficients of the spherical QD increase for transitions between higher states.     

Integral cross sections for electron impact excitations of argon and carbon dioxide

Electron-impact excitation integral cross sections play an important role in understanding the energy transfer processes in many applied physics. Practical applications require integral cross sections in a wide collision energy range from the excitation threshold to several keV. The recently developed BE-scaling method is able to meet the demands of integral cross sections for dipole-allowed transitions while the prerequisite relies on the accurate generalized oscillator strengths. Fast electron and x-ray scatterings are the conventional experimental techniques to approach the generalized oscillator strengths, and the joint study by both methods can provide credible cross-checks. The validated generalized oscillator strengths can then be used to extrapolate optical oscillator strengths by fitting the data with the Lassettre formula. The fitted curve also enables the integration of generalized oscillator strengths over the whole momentum transfer region to obtain the BE-scaled integral excitation cross sections. Here, experimental measurements by both fast electron and x-ray scattering of argon and carbon dioxide are reviewed. The integral cross sections for some low-lying states are derived from the cross-checked generalized oscillator strengths for the first time. The integral cross sections presented in this paper are openly available at https://doi.org/10.11922/sciencedb.01466.     

掺Er~(3+)硼硅酸盐玻璃的吸收光谱与J-O理论分析

采用高温熔融法制备了不同Er3+掺量的硼硅酸盐玻璃。测量和分析了玻璃样品的光密度和吸收光谱,并用最小二乘法拟合了实验与理论吸收谱线。应用Judd-Ofelt理论计算了光谱参数Ωλ(λ=2,4,6)和Er3+的振子强度,计算了拟合过程中的均方根偏差(δ),并讨论了Er3+浓度对对光密度和Ωλ参数的影响。分析结果表明:当Er2O3含量为21mol%时,玻璃在达到了较高的光密度(D0.53=4.0)的同时,Ω2亦达到最大值。此时玻璃中Er3+所处环境的对称性降低而共价性增强。     

Be^+离子和Li原子极化率和超极化率的理论研究

利用相对论模型势方法计算了Be^+离子和Li原子的波函数、能级和振子强度,进一步得到了基态的电偶极极化率和超极化率,并详细地分析了不同中间态对基态超极化率的贡献.对于Be^+离子,电偶极极化率和超极化率与已有的理论结果符合得非常好.对于Li原子,电偶极极化率与已有的理论结果符合得很好,但是不同理论方法计算给出的超极化率差别非常大,最大的差别超过了一个数量级.通过分析不同中间态对Li原子基态超极化率的贡献,解释了不同理论结果之间有较大差异的原因.     

Influence of solvent and intramolecular relaxation on dynamics of luminescence spectra in donor–acceptor complexes

The oscillator strengths for Rydberg states of a NaHe molecule are calculated using a semianalytic procedure with the l-coupling effect taken into account (due to the dipole potential of a core). This effect gives rise to nonzero oscillator strengths for transitions forbidden in the atomic model of molecular Rydberg states. The difference between calculations in terms of the atomic model and calculations with consideration of the dipole moment of a core is shown for allowed transitions.     

紫外吸收温差光谱特性与化合物的电子跃迁类型

用紫外吸收变温光谱差减法获得化合物的紫外吸收温差光谱（UVSDT）。测量了系列化合物的温差光谱。结果表明,UVSDT具有很强的特征性：n→σ^*电子跃迁的UVSDT单边红移,温差增大峰强度增加、红移增大;n-π^*电子跃迁的UVSDT为正、负两峰、温差增大,正负两峰各自向正、负方向增强;π-π^*电子跃迁的UVSDT为负峰,温差增大,峰强负向增大,峰位不移动。     

Ab initio calculations of exciton effects in optical spectra of an α-B<Subscript>12</Subscript> crystal

The dielectric functions and energy loss spectrum of electrons of a rhombohedral α-B₁₂ crystal are studied both in the single-particle and many-particle approximations using Bethe–Salpeter equations. The opposite roles of different contributions to exciton effects are discussed. The anisotropy of dielectric functions is shown, which demonstrates their high sensitivity with respect to the three-dimensional packing of icosahedrons. The influence of the coherent mixing of electronic and exciton states on the redistribution of oscillator strengths is found. The position of the plasmon of valence electrons and the high-frequency permittivity are found to be consistent with experimental data. The correlation between the distribution of oscillator strengths and features of the density of electronic states is discussed.     

Inverse hook method for measuring oscillator strengths for transitions between excited atomic states [1]

We describe an effective new method to measure the oscillator strengths for transitions between the excited states of atoms. The oscillator strength is determined, by measuring changes in the angular distribution or polarization of fluorescence light emitted by atoms in the initial or final state of the transition of interest, after these atoms have been subject to the a.c. Stark shift of an off-resonant laser pulse. The physics of the situation is very similar to that of the conventional hook method with this difference: the roles of the atoms and the photons have been interchanged. We therefore call this new methodthe inverse hook method. The inverse hook method is relatively insensitive to the details of the atomic absorption lineshape and also to the temporal and spectral profile of the laser pulse. It yields absolute oscillator strengths and it is especially suitable for measurements of transitions between excited atomic states, including autoionizing states.     

Energy and Oscillator Strength of V20+ Ion

The ionization potentials and fine structure splittings of 1s² nl (l = s, p, and d; n ⩽ 9) states for lithium-like V²⁰⁺ ion are calculated by using the full-core plus correlation (FCPC) method. The quantum defects of these three Rydberg series are determined according to the single-channel quantum defect theory (QDT). The energies of any highly excited states with n ⩾ 10 for these series can be reliably predicted using the quantum defects that are function of energy. The dipole oscillator strengths for the 1s²2s–1s² np and 1s²2p–1s² nd (n ⩽ 9) transitions of V²⁰⁺ ion are calculated with the energies and FCPC wave functions obtained above. Combining the QDT with the discrete oscillator strengths, the discrete oscillator strengths for the transitions from the given initial state to highly excited states (n ⩾ 10) and the oscillator strength density corresponding to the bound-free transitions are obtained. Translated from Chinese Journal of Atomic and Molecular Physics, 2005(2) (in Chinese)     

Mg原子振子强度与能级寿命的势模型计算

本文用一种有解析形式的势模型波函数计算了M g 原子的振子强度和能级寿命, 并与实验和其他理论计算结果作了比较.结果表明对于Mg 原子大量组态混合程度很弱的态, 用单组态波函数进行计算是完全可行的。 关键词：     

类锂离子(Z=11～20)32D-n2F偶极跃迁的振子强度

利用全实加关联方法得到的波函数计算类锂离子(Z=11～20)1s23d-1s2nf(4≤n≤9)的偶极跃迁振子强度,三种规范下的计算结果符合的很好.将分立态的振子强度结果与单通道量子亏损理论相结合,计算在电离阈附近(|E|≤I/2)分立态间的束缚态-束缚态跃迁振子强度与束缚态-连续态跃迁的振子强度密度,实现了具有较大核电荷数的类锂离子量子跃迁特性的全能域理论预言.     

Sc+18离子的跃迁能和振子强度

用全实加关联方法计算了Sc⁺¹⁸离子1s²2s--1s²np (2≤n≤9) 和1s²2p--1s²nd (3≤n ≤9)的跃迁能和振子强度。1s²np和1s²nd 态的精细结构劈裂通过计算自旋-轨道及自旋-其他轨道相互作用算符的期待值加以确定。还得到了这两个里德堡系列的量子亏损（作为能量的函数）。依据三种规范的振子强度公式得到的计算结果相当好的一致。将这些计算结果与量子亏损理论相结合，进一步得到电离阈附近的分立态-分立态跃迁的振子强度和分立态-连续态跃迁的振子强度密度。