Theoretical study on the transition properties of AlF

Potential energy curves of the X$^{1}\Sigma ^{+}$ and A$^{1}\Pi $ states of the AlF molecule are studied through the combination of the multi-reference configuration interaction (MRCI) approach and Davidson corrections (MRCI$+$Q). The AWCV5Z basis set is employed in the calculations. The transition dipole moments (TDMs) of the A$^{1}\Pi \leftrightarrow {\rm X}^{1}\Sigma^{+}$ transition are explored based on the AWCV5Z basis set and (4, 2, 2, 0) active space. The Schrödinger equation is solved via the LEVEL 8.2 program, and the vibrational levels and rotational constants of the X$^{1}\Sigma^{+}$ and A$^{1}\Pi $ states are calculated. It is shown that the AlF molecule has high diagonal Franck-Condon factors ($f_{00}=0.9949$ and $f_{11}=0.9854$) and large Einstein coefficients for the transition of A$^{1}\Pi {(\nu }'=0)\leftrightarrow {\rm X}^{1}\Sigma^{+}{\rm (\nu }'=0)$. In addition, the radiative lifetimes of the vibrational levels are close to 10$^{-9}$ s for the A$^{1}\Pi $ state. The line intensities of the A$^{1}\Pi {\rm (\nu }'=4-15)\leftrightarrow {\rm X}^{1}\Sigma^{+}{\rm (\nu }'=0)$ transitions are also calculated. The calculated TDMs and transition probabilities in this work are credible and provide some guidance for the study of similar transitions, particularly for exploring interstellar space.     

Synthesis,tautomeric stability,spectroscopy and computational study of a potential molecular switch of (Z)-4-(phenylamino)pent-3-en-2-one

The (Z)-4-(phenylamino) pent-3-en-2-one (PAPO) was synthesised applying carbon-based solid acid and described by experimental techniques. Calculated results reveal that its keto-amine form is more stable than its enol-imine form. A relaxed potential energy surface scan has been accomplished based on the optimised geometry of NH tautomeric form to depict the potential energy barrier related to intramolecular proton transfer. The spectroscopic results and theoretical calculations demonstrate that the intramolecular hydrogen bonding strength of PAPO is stronger than that in 4-amino-3-penten-2-one)APO(. In addition, molecular electrostatic potential, total and partial density of stats (TDOS, PDOS) and non-linear optical properties of the compound were studied using same theoretical calculations. Our calculations show that the title molecule has the potential to be used as molecular switch.     

Time-dependent density functional theory study on excited state intramolecular proton transfer of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one

The time-dependent density functional theory (TDDFT) method was carried out to investigate the excited state intramolecular proton transfer (ESIPT) process of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one (1a). 1a has two tautomeric forms: one is 1a(O), which is induced by intramolecular hydrogen bond O-H?O=C, and the other one is 1a(N), which is caused by intramolecular hydrogen bond O-H?N. From excited state to tautomer excited state coming from ESIPT, the hydroxyl hydrogen breaks away and the dissociated hydrogen adsorbed on pyridinic nitrogen or carbonyl oxygen formed new intramolecular HB and the corresponding bond length and bond angle varied greatly. In comparison, a similar process of proton transfer for 1a(N)H⁺ protonated 1a(N) from ground state to excited state was obtained. This detailed proton transfer mechanism was provided by molecular orbitals analysis and it may be applied to molecular switch and organic Lewis acid/base. We investigated the excited state proton transfer mechanism of the four molecules through the theoretical method for the first time and gave unambiguous geometry of excited state.     

Theoretical study of the SrLi+ molecular ion: structural,electronic and dipolar properties

ABSTRACT

The structural and electronic properties of (SrLi)⁺ molecular ion have been determined by the use of ab initio approaches. Potential energy curves (PECs) with their spectroscopic constants (R_e, D_e, ω_e, T_e, B_e and ω_eχ_e) have been calculated. Also, the vibrational properties and the electric dipole moments, either permanent (PDM) or transition (TDM) ones, have been investigated and analysed. Large Gaussian basis sets, the full valence configuration interaction (FCI) and the formalism of non-empirical pseudo-potential including the two approaches, effective core potential (ECP) and core polarisation potential (CPP), are analysed. Therefore, (SrLi)⁺ is considered as a two effective electrons system. Numerous excited states of symmetries ^1,3Σ⁺, ^1,3Π and ^1,3Δ dissociating below the ionic limit Sr²⁺Li^? have been investigated. This study shows interesting behaviours around the avoided crossing related to charge transfer involving important processes in physics and astrophysics such as dynamics, pre-dissociation and inelastic transitions.     

An integrated approach to the study of the tautomerism of 4‐((Phenylimino)methyl) naphthalene‐1‐ol

The aim of the current report is to shed light on the tautomerism of 4‐((Phenylimino)methyl) naphthalene‐1‐ol in solution, which was studied by UV–Vis spectroscopy and quantum chemical calculations. It was found that this compound does not have the typical tautomeric behavior of its analog 4‐Phenylazo‐naphthalen‐1‐ol. The complicated equilibrium between the enol‐ and keto‐like forms and two kinds of dimers that can exist in solution, is strongly dependent on the proton acceptor/donor abilities of the solvent. Using advanced data treatment quantitative information about the tautomeric and dimeric equilibrium constants was obtained. Copyright © 2007 John Wiley & Sons, Ltd.     

Theoretical study of keto–enol tautomerism by quantum mechanical calculations (the QM/MC/FEP method)

In this study, the tautomeric equilibrium between the keto and enol forms has been studied for five typical ketones and aldehydes: i‐butanal, acetaldehyde, acetone, acetylacetone, and dimedone. The level of theory used in the gas‐phase calculation was Becke, three‐parameter, Lee–Yang–Parr/6‐311G(d,p)//Becke, three‐parameter, Lee–Yang–Parr/6‐31G(d). The free energies of solvation were included in the calculation by using the free‐energy perturbation method based on Monte Carlo simulation, that is, the quantum mechanical/Monte Carlo/free‐energy perturbation method. Three different models, incorporating no‐water, one‐water, and two‐waters, were adopted. The results showed that in the gas phase the addition of water molecules to the reaction mechanism caused the activation barriers (ΔG^?_gas) to decrease by half relative to the water‐free mechanism, but there was no effect on the relative difference in free energy, ΔG_gas. The solvation effects (ΔG_sol), based on quantum mechanical/Monte Carlo/free‐energy perturbation calculations, were added to those of the gas‐phase results of the one‐water and two‐waters models. The two‐waters model produced values that were very consistent with the experimental data for all of the tautomers. The differences in the relative Gibbs free energy (ΔG_rxn) were less than 1.0 kcal mol^–1. In summary, the inclusion of solvent molecules in gas‐phase calculations plays a very important role in producing results consistent with experimental data. Copyright © 2012 John Wiley & Sons, Ltd.     

Theoretical kinetics study of thymine tautomerism and interaction of Na+ with its tautomers

The current work is a theoretical study of the tautomerism of thymine in the gas phase. Eighteen structures were found in the isomerisation reaction of thymine, some of which are reported for the first time. Thirty hydrogen transfer reactions were carried out. In 24 of the reactions, the hydrogen abstractions N―H→O, N―H→C and C―H→O were considered. The potential energy surface for all trajectories was determined for 18 tautomers and 40 transition states. The RRKM-TST model was used to calculate the rate constants of the reactions to examine their kinetics. Nonlinear least-squares fitting was used to calculate the rate constants expressions. The interaction of sodium ion and tautomers in the gas phase was also investigated. Three types of interaction of metal cations with thymine were found. In the first, metal cations interact with a lone pair of nitrogen or oxygen tautomers. The second type is the interaction of metal cations with two nitrogen and oxygen of tautomers. The last type is the interaction of metal cations and the electron density of the π-system of thymine in which the metal ion is perpendicular to the ring of tautomers. The stability ranking of the thymine tautomers and their complexes was also determined.     

CO分子振转光谱的理论研究

采用从头算的多参考组态相互作用(MRCI)方法并结合基组aug-cc-pCVQZ计算了CO分子基态(X1Σ+)的势能曲线和偶极矩曲线,得到的势能曲线、偶极矩曲线分别与RKR势、文献的偶极矩曲线吻合较好。利用所得的势能,求解双原子分子核运动的Schrdinger方程找到了CO分子X1Σ+态转动量子数J=0时的70个振动态,对于每一振动态,分别计算了其振动能级G(v)、转动惯性常数B_v和离心畸变常数D_v,并把计算结果与已知的42个实验值做了详细比较,结果表明,计算的振动能级G(v)、转动惯性常数B_v、离心畸变常数D_v与实验值符合较好。利用G(v),B_v导出的光谱常数[谐振频率ω_e(2 160.1 cm-1)、非谐振频率ω_eχ_e(13.1 cm-1)、转动常数B_e(1.918 cm-1)、振转耦合常数α_e(0.017 3 cm-1)]也与实验值的光谱常数[ω_e(2 169.8 cm-1),ω_eχ_e(13.3 cm-1),B_e(1.931 cm-1),α_e(0.017 5 cm-1)]较为符合,这在一定程度上证明了方法MRCI/Aug-cc-pCVQZ对CO分子基态性质的计算是合适而可靠的。利用乘积近似方法计算了CO分子在常温、中温、高温时的配分函数,在此基础上,计算了CO分子在T=296 K时的1-0跃迁带的谱线强度,通过比较发现,计算所得的线强度与HITRAN数据库符合较好。进一步计算的CO分子X1Σ+态1-0,2-0,3-0,4-0,2-1,3-1和4-1跃迁带的带强度也与实验值较为吻合,同时首次计算了CO分子X1Σ+态3-2跃迁带、4-2跃迁带的线强度及带强度。     

DTO体系分子反应动力学

基于DTO分子( 1A1)的氢同位素效应,得到修正的Born-Oppenheimer(B-O)理论下多体展式分析势能函数.用准经典的Monte-Carlo轨迹法研究了D+ TO(0 ,0)和T+ DO(0 ,0)的分子反应动力学过程.结果表明:在碰撞能量较低时( < 209.2 kJ. mol - 1 ),D+ TO(0 ,0)和T+DO(0,0)反应主要生成O+ DT,并且该反应是无阈能的;有少量的交换反应产物DO (TO)生成,并伴有极少量的络合物产生.碰撞能大于209.2kJ . mol - 1后,逐渐出现分子被完全碰散成D,T ,O 原子的情形.反应 D+TO(0 ,0) →OD + T和 T +DO(0 ,0) →OT + D是无热反应但是有阈能存在.由于D和T原子的同位素效应,置换产物轨线存在非一致性.     

Theoretical study of structural energy, phonon spectra, and elastic constants of Rh and Ir

The transition metal pair potential (TMPP) is used to study band structure energy of Rh and Ir. Both metals are found to be most stable in fcc structure down to atomic volume 0.5V ₀. The pressure at 0.5V ₀ is found to be 5.235 Mbar and 9.216 Mbar in Rh and Ir, respectively. The TMPP is also used to study other properties of these metals like cohesive energy, phonon frequencies at observed volume. The bulk moduli and elastic constants of these metals at observed volume are calculated by including the volume contribution.     

Gas‐phase equilibrium constants for the thermally initiated oxidation of hexafluoropropene with molecular oxygen

Equilibrium constants for a kinetic model of the thermally initiated gas‐phase oxidation of hexafluoropropene have been calculated in the temperature range of 463–493 K based on the thermochemical properties of the reactive species. Standard molar enthalpies and entropies of formation as well as heat capacities of trifluoroacetyl fluoride, hexafluorocyclopropane, hexafluoropropene, and hexafluoropropene oxide were predicted using methods of quantum statistical mechanics. These along with literature data for remaining species involved allowed for calculating reaction enthalpies of individual steps of the proposed reaction mechanism. The calculations were performed at the G4 B3LYP/6‐31G(2df,p) level of theory. The enthalpy of formation was determined using both the atomization method and isodesmic reaction schemes. All reactions apart from the decomposition of hexafluoropropene oxide were found to be exothermic. Only the hexafluoropropene oxide decomposition reaction was found to be noticeably reversible under the reaction conditions considered. This was confirmed through independent experimentation and kinetic model identification. Copyright © 2015 John Wiley & Sons, Ltd.     

SiH2体系的分子反应动力学

基于多体展式方法所导出的SiH₂（X¹A₁）分析势能函数,用准经典的Monte Carlo轨线法研究了Si（¹D_g）+H₂（0,0）和H（²S_g）+SiH（0,0）的原子与分子反应动力学过程.研究结果表明：Si（¹D_g）与H₂（0,0）的碰撞在低能时（小于209.20 kJ/mol）生成稳定的络合物SiH₂（X¹A₁）,该反应是无阈能反应;而H（²S_g）与SiH （0,0）碰撞不能生成稳定的络合物,主要发生交换反应H（²S_g）+SiH （0,0）→Si（¹D_g）+H₂（0,0）,该反应也是无阈能反应. 关键词： 2')" href="#">SiH₂ 势能函数 反应截面 轨线     

Spectroscopic and quantum-mechanical study of enol-enol tautomerism of 3-acetyltetramic acid derivatives

By the method of IR spectroscopy, Raman spectroscopy, and nonempirical (basis 3-21G//3-21G(d,p)) and semiempirical (approximations AM1 and PM3) quantum-mechanical methods the tautomeric structure of a series of 3-acetyltetramic acid derivatives has been investigated. It is shown that all the investigated compounds exist in vapor, in solution, and in the crystalline state mainly in the form of exo-enols among which the prevalent form is that in which lactam carbonyl participates in intrachelate hydrogen bonding. Complete series of relative stabilities of possible tautomeric forms of the investigated compounds have been established. General conlusions on the structure of 5-membered ring β,β′-triketones have been formulated. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 154–161, March–April, 2000.     

U+CO体系的分子反应动力学研究

基于CUO分子(X3A″)的多体展式分析势能函数,用准经典的MonteCarlo轨迹法研究了U+CO(0,0)的分子反应动力学过程.结果表明:在碰撞能低时(<215kJ.mol-1),可以生成长寿命络合物CUO(X3A″),并且该络合反应是无阈能反应,这一结论与前文用多体项展式理论计算的CUO分子势能曲线结果一致.碰撞能大于4184kJ.mol-1后,逐渐出现置换产物UO和UC,随碰撞能进一步增大,分子将被完全碰散成U,C,O原子,而且反应U+CO(0,0)→UO+C,U+CO(0,0)→UC+O和U+CO(0,0)→U+O+C是有阈能反应基于CUO分子(X3A″)的多体展式分析势能函数,用准经典的MonteCarlo轨迹法研究了U+CO(0,0)的分子反应动力学过程.结果表明:在碰撞能低时(<215kJ.mol-1),可以生成长寿命络合物CUO(X3A″),并且该络合反应是无阈能反应,这一结论与前文用多体项展式理论计算的CUO分子势能曲线结果一致.碰撞能大于4184kJ.mol-1后,逐渐出现置换产物UO和UC,随碰撞能进一步增大,分子将被完全碰散成U,C,O原子,而且反应U+CO(0,0)→UO+C,U+CO(0,0)→UC+O和U+CO(0,0)→U+O+C是有阈能反应 关键词： 玻色-爱因斯坦凝聚体 V型三能级原子 双模压缩态光场 光场正交压缩     

Theoretical study of the structured blue emission of PbWO 4

The experimentally observed structure in the blue emission of PbWO 4 crystals is analyzed theoretically. The full interaction Hamiltonian, including ligand field, Jahn-Teller, pseudo Jahn-Teller, and spin-orbit interactions is considered. The emission-band shape is numerically calculated using Monte-Carlo integration using both semiclassical and quantum-mechanical approaches. Theoretical results are qualitatively compared to experimentally observed spectra.     

Theoretical study of the molecular properties of benzyl azide, 2-, 3- and 4-methyl benzyl azide

Ab initio and density functional calculations have been performed to study the benzyl azide, 2-, 3- and 4-methyl benzyl azides. Several molecular properties, such as conformational equilibrium, optimal geometry, and vibrational frequencies, have been computed for these molecules. Ionisation energies were also computed.     

2,3-二取代喹唑啉-4(3H)-酮化合物结构和活性的密度泛函理论研究

采用密度泛函理论中的广义梯度近似(DFT/GGA)方法,在PW91/DNP水平上研究了21种2,3-二取代喹唑啉-4(3H)-酮化合物的结构、化学活性和前线轨道.结果表明:此类化合物的能隙E_g大部分都在3.50~3.60 e V之间,其中在喹唑啉环3位上取代甲氧基苄基,或是在8位上取代甲基,化合物的能隙降低,而且甲氧基在苄基的间位比对位降低得更厉害.通过比较还发现,2,3-二取代喹唑啉-4(3H)-酮化合物对水稻纹枯菌(Rhizoctonia solani bacteria)的杀菌活性与哌啶并噻吩并嘧啶酮衍生物对水稻纹枯菌的杀菌活性相当,而哌啶并噻吩并嘧啶酮衍生物比2,3-二取代喹唑啉-4(3H)-酮化合物对苹果轮纹病(Botryospuaeria gregaria bacteria)杀菌活性好.     

Theoretical study on the band structure and optical properties of 4H-SiC

We have studied the band structure and optical properties of 4H-SiC by using a full potential linearized augmented plane waves (FPLAPW) method. The density of states (DOS) and band structure are presented. The imaginary part of the dielectric function has been obtained directly from the band structure calculation. With band gap correction, the real part of the dielectric function has been derived from the imaginary part by the Kramers－Kronig (KK) dispersion relationship. The values of reflectivity for normal incidence as a function of photon energy have also been calculated. We found the theoretical results are in good agreement with the experimental data.     

Theoretical study of conformational transition of CDK4 by association of cyclin D3

ABSTRACT

We present coarse-grained simulations to investigate folding and association of cyclin-dependent kinase 4 (CDK4) with cyclin D3. In our simulations, the Gō-like model and our coarse-grained model are applied to describe intramolecular and intermolecular interaction of protein molecules, respectively. We investigate conformational stability of each state of CDK4 with/without association to cyclin D3 on a single basin potential with reference to each state of CDK4. The results of simulations for the native CDK4 with cyclin D3 are consistent with an experimental observation. The open CDK4 may associate to cyclin D3 on a different interface from cyclin D3-native CDK4 complex structure. If the open CDK4 associates to cyclin D3, the open CDK4 can slightly fold and become smaller, suggesting an unfolded intermediate. After a double-basin potential with reference to the native and open states of CDK4 is given, the open CDK4 associated with cyclin D3 can smoothly shift to the native CDK4. We propose a structure of a potential candidate of an unfolded intermediate during activation of CDK4.