Theoretical calculation about the valence and Rydberg excited states of hydrogen cyanide

The singlet and triplet excited states of hydrogen cyanide have been computed by using the complete active space self-consistent field and completed active space second order perturbation methods with the atomic natural orbital (ANO-L) basis set. Through calculations of vertical excitation energies, we have probed the transitions from ground state to valence excited states, and further extensions to the Rydberg states are achieved by adding 1s1p1d Rydberg orbitals into the ANO-L basis set. Four singlet and nine triplet excited states have been optimized. The computed adiabatic energies and the vertical transition energies agree well with the available experimental data and the inconsistencies with the available theoretical reports are discussed in detail.     

Structures of Rydberg transitions in the absorption spectra of methyl-substituted derivatives of bis(η6-benzene)chromium

The effect of methylation of ligands in bis(η⁶-benzene)chromium (1) on the structure of Rydberg transitions in absorption spectra has been studied. A detailed analysis and interpretation of all Rydberg elements of the vapor-phase spectra of bis(η⁶-benzene)chromium (2), bis(η⁶-o-xylene)chromium (3), bis(η⁶-m-xylene)chromium (4), and bis(η⁶-mesitylene)chromium (5) was carried out. The vapor-phase electronic absorption spectrum of bis(η⁶-p-xylene)chromium (6) was measured, and the assignment of the Rydberg bands was made for the first time. The first ionization potentials of complexes 2–5 were refined. The energy of detachment of the 3d_z ² electron and the parameters of the Rydberg excitations for molecule 6 were determined. The vibronic components of the 3d_z ²→R4p _x,y transition in the spectra of complexes 2 and 6 were assigned. The differences in the Rydberg structure of the spectra of compounds 2–6 were analyzed in terms of the selection rules for optical transitions in the corresponding symmetry groups. The vapor-phase spectra correspond to conformers with the symmetry groupsC _2v andC ₂ for complexes 2–4, with the symmetry groupsD _3h andD ₃ for compound 5, and with the symmetry groupD _2d for complex 6. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 897–903, May, 1998.     

Theoretical study on the gas‐phase reactivity of halogenated alkylperoxyl radicals toward alkenes

The electrophilic additions of hydroperoxyl (HO ${}_{\text{2}}^{\text{⋅}}$), alkylperoxyl (RO ${}_{\text{2}}^{\text{⋅}}$), and halogenated alkylperoxyl radicals to ethylene were studied using the AM1 and PM3 semiempirical MO methods at the SCF/UHF level. Reactantlike transition states were predicted for the title additions. The AM1 activation enthalpies (ΔH ${}_{\text{f}}^{\text{*}}$) were found to be increased in the order HO ${}_{\text{2}}^{\text{⋅}}$<CH₃O ${}_{\text{2}}^{\text{⋅}}$<C₂H₅O ${}_{\text{2}}^{\text{⋅}}$<i‐C₃H₇O ${}_{\text{2}}^{\text{⋅}}$. The reactivity of an alkylperoxyl radical toward ethylene was found to be increased as the degree of halogen substitution on the alkyl group increased. A good correlation was established between ΔH ${}_{\text{f}}^{\text{*}}$ and the Taft polar substituent constants, σ*. The Evans–Polanyi correlation between ΔH ${}_{\text{f}}^{\text{*}}$ and ΔH ${}_{\text{r}}^{\text{°}}$ was justified and the validity of the Hammond postulate was indicated. The calculated results were compared with the available experimental findings. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 273–283, 1999     

Performance of time-dependent density functional and Green functions methods for calculations of excitation energies in radicals and for Rydberg electronic states

Time-dependent density functional (TD-DFT) and perturbation theory-based outer valence Green functions (OVGF) methods have been tested for calculations of excitation energies for a set of radicals, molecules, and model clusters simulating points defects in silica. The results show that the TD-DFT approach may give unreliable results not only for diffuse Rydberg states, but also for electronic states involving transitions between MOs localized in two remote from each other spatial regions, for example, for charge-transfer excitations. For the. O-SiX(3) clusters, where X is a single-valence group, TD-DFT predicts reasonable excitation energies but incorrect sequence of electronic transitions. For a number of cases where TD-DFT is shown to be unreliable, the OVGF approach can provide better estimates of excitation energies, but this method also is not expected to perform universally well. The OVGF performance is demonstrated to be satisfactory for excitations with predominantly single-determinant wave functions where the deviations of the calculated energies from experiment should not exceed 0.1-0.3 eV. However, for more complicated transitions involving multiple bonds or for excited states with multireference wave functions the OVGF approach is less reliable and error in the computed energies can reach 0.5-1 eV.     

CH_3SH+CN微观反应机理的理论研究

采用BMC-CCSD//B3LYP/6-311G(d,p)方法对CH3SH+CN反应机理进行了详细的理论研究.反应中涉及的各稳定点的构型、振动频率和零点能在B3LYP/6-311G(d,p)水平下计算得到,计算结果表明,该反应存在两种反应机理,5条可能的反应通道.SN2机理由于能垒太高,与直接氢抽提机理相比可以忽略.该反应的最可行通道为CN中的C原子进攻SH中的H原子经由一个前期和一个后期分子络合物生成产物CH3S和HCN.计算得到的反应焓变与已有实验值非常吻合.     

Theoretical study of low-lying electronic states and emission spectra of the excimer ions NaHe and NaNe

Ab initio CASSCF calculations using the Gaussian basis set aug_cc_pVTZ developed by Dunning et al. specifically for calculations at the post-HF level was carried out for excimer NaHe⁺ and NaNe⁺ ions in order to determine spectroscopic characteristics and radiation lifetimes of their low-lying excited electronic states. The computed emission spectra of these were shown to be in good agreement with the experimental ones observed recently by Hammer et al. (Hyperfine Interactions 88 (1994) 151). Contrary to the earlier popular opinion, all excited electronic states of these ions, correlating with the limit Rg⁺+Na, and not just the radiating singlet states turn out to be bound. It was shown that under the conditions of an experiment similar to the one performed by Hammer et al., the excited triplet NaHe⁺(1³Σ⁺) states can decay as a result of their interactions with a high-energy Ar⁺ beam. This decay has to be accompanied with the formation of the ions He⁺, which in turn can interact with sodium atoms to yield the radiating NaHe⁺(2¹Σ⁺) states again and, thus to maintain the emission observed in the experiment.     

Theoretical study on halide and mixed halide Perovskite solar cells: Effects of halide atoms on the stability and electronic properties

Increasing the stability of perovskite solar cells is one of the most important tasks in the photovoltaic industry. Thus, the structural, energetic, and electronic properties of pure CH₃NH₃PbI₃ and fully doped compounds (CH₃NH₃PbBr₃ and CH₃NH₃PbCl₃) in cubic and tetragonal phases were investigated using density functional theory calculations. We also considered the effects of mixed halide perovskites CH₃NH₃PbI₂X (where X = Br and Cl) and compared their properties with CH₃NH₃PbI₃. The DFT results indicate that the phase transformation from tetragonal to cubic phase decreases the band gap. The calculated results show that the X‐site ion plays a vital role in the geometrical stability and electronic levels. An increase in the band gap and a reduction in the lattice constants are more apparent in CH₃NH₃PbI₂X compounds (I > Br > Cl).     

Similarities in the Intensities of Analogous Rydberg–Rydberg Transitions in the Molecular Series CF x Cl y (x=3, 2, 1; y=1, 2, 3)

In this work, the photoabsorption behaviour of the molecular series CF₃Cl, CF₂Cl₂ and CFCl₃, involving their ground state and two different Rydberg series, has been studied. The discrepancies or similarities in the intensities of homologous transitions in the three CF _x Cl _y molecules have been analysed on account of their electronic structure. Absorption oscillator strengths have been calculated with the Molecular quantum defect orbital (MQDO) approach. Electronic transitions between states belonging to two different unperturbed Rydberg series of the same molecule have been calculated by us for the first time. The quality of the achieved oscillator strengths has been assessed by comparison with, to our knowledge, scarce experimental data available in the literature, through analysis of the discrepancies or similarities in the intensities of homologous transitions in the molecular series CF _x Cl _y when states of different type are involved, and by testing the compliance of regularities by the Rydberg series object of our study.Article for the special issue dedicated to J.-P. Malrieu     

Two-colour bound—free—bound spectroscopy of the [E1/2]c6S Rydberg states of CH3I and CD3I

In this resonantly enhanced multiphoton ionization (REMPI) experiment, an extended vibrational progression in the CI stretching mode (v₃) of methyl iodide (-h₃ and -d₃) is observed in the 1 + 1′ excitation of the [1/2] 6s; 0 Rydberg state when the pump photon wavelength lies in the bound → free absorption continuum. This is in contrast with one-colour coherent (non-resonant) two-photon excitation, where the v₃ mode is not excited. By working at several different fixed probe wavelengths and scanning the pump frequency, the relative contributions from the three intermediate repulsive states can be explored through changes in the relative strengths of the Ω = 0 and 1 components of the final Rydberg states. Extensive predissociation in the Rydberg states curtails the vibrational progression.     

秋水仙碱立体异构体电子结构及圆二色谱性质的理论研究

采用量子化学密度泛函理论(DFT)在B3LYP/6-311++G二水平上对秋水仙碱四个立体异构体分子几何构型进行了优化,在优化的基础上进行了振动圆二色谱(VCD),紫外-可见光谱(UV-Vis)和电子圆二色谱(ECD)研究.为模拟真实条件,以水为溶剂,计算其对分子电子结构和光谱性质的影响.研究结果表明:秋水仙碱四个立体...     

CH3NO2异构化反应的理论研究

利用密度泛函和电子密度拓扑分析方法对CH3NO2 (NM)的异构化反应进行了研究。 找到了九种可能的异构体和八个反应通道。通过内禀反应坐标(IRC)分析确认了过渡态与异构体之间的连接关系。计算结果表明,在CH3NO2→CH3ONOt反应过程中,过渡态为紧密结构(在整个反应过程中CH3NO2没有分解为CH3 和NO2 ),与Arenass等人的结论一致。在CH3NOOc→CH2NOOH反应过程中,存在有一个含有四元环→五元环→四元环→五元环变化过程的结构过渡区,这也是在反应过程中首次发现五元环状过渡结构。     

Theoretical Studies on Reaction Mechanism of CH3SO with NO

The potential energy surface （PES） of CH3SO radical with NO reaction has been studied at MP2/6-311G（2df, p） and QCISD/6-311G（2df, p） levels. Geometries of the reactants, transition states （TS） and products were optimized at B3LYP/6-311G （d,p） level. The geometries of the transition states were found for the first time. The calculated results show that the reaction can proceed via singlet-state or triplet-state PES. Because of the high energy barrier of triplet surface, the singlet surface reactions are dominant. The topological analysis of electron density shows that there are two kinds of structaral transition states （the bifurcation-type ring structure transition state and the T-shaped conflict structure transition state） in the titled reaction. The total electronic density of the reactants, TS and products and the spin electronic density on the triplet surface were also discussed in this paper.     

CH3S与CO反应机理的理论研究

在G3(MP2)//B3LYP/6-311 G(d,p)水平上,对CH3S自由基与CO气相反应的微观机理进行了理论研究.结果表明:该反应共存在3个反应通道,产物分别为CH3 OCS,CH2S HCO和CH2S HOC.由于形成产物CH3 OCS的活化势垒较低,因此为主要反应通道,这与实验观察到的结果是一致的.     

Theoretical study on the reaction mechanism of(CH_3)_3CO+CO

The global environment pollution includes pho-tochemical smog, acid rain and stratospheric ozonedepletion. The short-lived species/radicals in atmos-phere are closely related to these phenomena. Theshort-lived species/radicals bring the photochemicalsmog,…     

Theoretical study on the reaction of (Z)‐CF3CHCHCF3 with OH radicals

The mechanism on the OH‐initiated atmospheric oxidation reaction of (Z)‐CF₃CH?CHCF₃ with and without O₂/NO has been investigated theoretically. The electronic structure information of the potential energy surface was obtained at the M06‐2X/aug‐cc‐pVDZ level, and the single‐point energies were refined by MCG3/3 method. The calculations show that the (Z)‐CF₃CH?CHCF₃ + OH reaction occurs via addition‐elimination mechanism, leading to products CF₃ and CF₃CH?CH(OH), rather than H‐abstraction mechanism at low temperature. Under atmospheric condition, the OH‐addition intermediate is likely to react rapidly with O₂/NO, and the likely products are CF₃C(O)H, CF₂(O), CF₃CH(OH)CH(O), FNO, and HO₂, as is proposed by experiment. © 2013 Wiley Periodicals, Inc.     

Theoretical study of the polarized electronic absorption spectra of vanadium-doped zircon

The polarized electronic absorption spectra of a blue vanadium-doped zircon single crystal, grown by the flux method, has been studied by quantum chemical (CI) calculations in order to determine the position of the V⁴⁺ dopant in the zircon host structure. Particularly, the excitation energies and polarizations of V⁴⁺ occupying alternate positions, either the zirconium or silicon position or the interstitial site 16g, have been considered. It is concluded that the observed electronic absorption spectra and the color of zirconblue can only be explained if the V⁴⁺ chromophore is placed on the respective interstitial position.     

Theoretical study on the structures and electronic spectra of TCNE2-.

Investigations into the charge-separated states and electron-transfer transitions in tetracyanoethylene (TCNE) complexes have recently generated much interest. In this work we present theoretical calculations showing that the most stable structure of the dianion TCNE2- has D2d symmetry in vacuum as well as in the solvents dichloromethane and acetonitrile. By means of the coupled cluster linear response, we compute the vertical electronic spectrum in both the gas phase and solution. The theoretical results are compared to the experimental data and good agreement is achieved.     

Computational insight into excited states of the ring-opening radicals from the pyrolysis of furan biofuels

The low-lying valence excited states and Rydberg states of the radical species from the ring-opening reactions in pyrolysis of furan biofuels have been determined by extensive density functional theory and sophisticated wave function theory calculations. The radicals 1-C₄H₅O-2, 2-furylCH₂, and 4-C₆H₇O with the delocalized π-type single electron are predicted to be most stable among the reactive species here for furan, 2-methyfuran, and 2,5-dimethylfuran, respectively. Predicted vertical transition energies by TD-CAM-B3LYP show good agreement with those by CASPT2. Some among the electronic excitations to low-lying states can take place in the visible light region, and they may be involved in the combustion process. Further surface hopping dynamics simulations on the excited states of the most stable ring-opening radical 1-C₄H₅O-2 of furan as an example reveal that 89.9% sampling trajectories at the initial excited state of 2²A”(π¹π*²) decay to the 1²A’(n¹π*²) state within an average of 384 fs, and then 81.2% trajectories at the 1²A’ state go to the ground state within an average of 114 fs. At the end of the simulation for 1000 fs, 18.8% trajectories still stay on the excited states of 2²A” and 1²A’, suggesting that the reactive radicals in the ground state are mainly responsible for the combustion chemistry of furan biofuels. © 2018 Wiley Periodicals, Inc.