Variational transition state theory with multidimensional tunnelling and kinetic isotope effects in the reactions of C2H6, C2H5D and C2D6 with .CCl3 to produce CHCl3 and CDCl3

ABSTRACT

Rate constants for the reactions of C₂H₆, C₂H₅D and C₂D₆ with .CCl₃. for the production of CHCl₃ and CDCl₃ (k₁, k₂, k₃ and k₄) were computed using variational transition state theory coupled with hybrid-meta density functional theory (MPWB1K) over the temperature range of 200–2900 K. The ground-state vibrational adiabatic potential was plotted for all channels. Small- and large-curvature tunnelling were determined to include quantum effects in the calculation of rate constants. Harmonic vibrational frequencies along the reaction path were calculated in curvilinear coordinates with scaled frequencies. Anharmonicity was included in the lowest-frequency torsion. The position of formation and dissociation of bonds was specified using the variation in harmonic vibrational frequencies along the reaction path. Representative tunnelling energy and the thermally averaged transmission probability at 298 K (P(E)exp?( ? ΔE/RT)) were determined for the reactions in which tunnelling is important. The kinetic isotope effect was used to calculate the considerable contributions of tunnelling and vibration. The expressions for rate constants were determined using nonlinear least-square fitting over the temperature range of 200–2900 K.     

Ab initio investigation of the electronic and vibrational properties for the (CaLi)+ ionic molecule

A wide adiabatic study has been performed for numerous electronic states of CaLi⁺ molecular ion. The adiabatic potential energy curves and their spectroscopic constants (R_e, D_e, ω_e and T_e) have been calculated using an ab initio approach including a nonempirical pseudo-potential for the Ca and Li cores with the core polarisation potentials operator through full configuration interaction (FCI). Thereafter, the energies of vibrational levels and their spacing for all these states have been reported. In addition, the electric dipole moment curves have been investigated for the (1-19) Σ, (1-12) Π and (1-8) Δ electric states. Moreover it lets us check the extreme transition dipole moments (TDM). These behaviours of TDM are more accustomed to estimate the radiative lifetimes for all vibrational levels in 2¹Σ⁺ and 3¹Σ⁺ states. Also, the bound-bound and the bound-free contribution have been calculated precisely and by employing a Franck–Condon (FC) approximation.     

Studies on the σ–hole bonds (halogen,chalcogen, pnicogen and carbon bonds) based on the orientation of crystal structure

ABSTRACT

The 4,7-dibromo-5,6-dinitro-2,1,3-benzothiadiazole (DDBT) crystal has two polymorphic forms [1 M.S. Pavan, A.K. Jana, S. Natarajan, and T.N. Guru Row, J. Phys. Chem. B 119, 11382 (2015).[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]], where the close contacts between two electronegative atoms are identified and studied through Hirshfeld surface analysis. Br---Br and O---O cut-off distances are addressed and analysed. The σ–hole of bromine, sulphur, oxygen atoms and π-hole of carbon and nitrogen atoms were subjected to study using molecular electrostatic potential map and 3D-deformation density map. Sixteen types of dimers from the two forms of crystal structure (6 for form I and 10 for form II) were studied using the charge transfer properties and interaction energies and made detailed analysis of halogen bond (Br---N), dihalogen bond (Br---Br), chalcogen bond (O---Br and S---Br), dichalcogen bond (S---O, O---S and O---O), pnicogen bond (N---O) and carbon bond (C---O and C---Br) interactions. The impact of orientations is discussed to define the type of interaction and its strength through charge transfer mechanism. The contribution of bond angle values for the σ-hole and π–hole bonds are discussed. Utilisation of σ–hole in smaller bond angle values (above 30°) of |θ₁ ? θ₂| existing in type II halogen–halogen bond have been examined in the two forms.     

Theoretical study of excited state proton transfer in pyrrole-2-carboxylic acid

Pyrrole 2-carboxylic acid (PCA) shows dual emission (310 nm and 430 nm) in water on photo-excitation, which indicates that more than one species is in the excited state. This paper reports on the quantum chemical analysis of pyrrole 2-carboxylic acid (PCA) in the light of a possible excited state proton transfer. Dipole moment, excited state energy and findings in molecular orbital calculations (HOMO, LUMO) establish that PCA is a likely candidate for transfer of a proton from the pyrrole moiety to the C=O of carboxylic moiety (possible zwitterionic form) in the excited state. Overall, the computed predicted results of intramolecular and intermolecular excited state proton transfer corroborates the experimental results.     

An accurate theory for the square-well potential: from long to short well width

Density function theory (DFT) is combined with the first-order mean spherical approximation (FMSA) to study the radial distribution function (RDF) of the square-well (SW) potential. The combination (DFT + FMSA) is based on the direct correlation function (DCF) of the FMSA. Upon comparison with computer simulation data, DFT + FMSA is shown to give better performance than FMSA for mid- and long-range attractions. For short-range and very short-range attractions, the theory successfully corrects the deficiencies of the original FMSA. Comparisons include the evaluation of contact values, gap height at a discontinuity and profiles of the RDF. This work provides an accurate and consistent way to handle the SW potential.     

激光场中极化势对电子-氦原子散射影响

构建含有极化势的静电屏蔽势和单纯的静电屏蔽势这两种原子势模型,应用第二玻恩近似（SBA）理论,分别对激光场中电子-氦原子散射截面进行了理论计算。对比实验结果发现含有极化势的静电屏蔽势给出的结果与实验符合较好。表明极化势在激光辅助电子-原子散射中起着重要作用。     

He原子与O2分子相互作用势及碰撞微分截面的研究

本文用量子力学从头算方法深入研究了He原子与O2分子的相互作用势,选定CCSD(T)/6-311++G(3df,2pd)方法和基组,同时采用了Boys和Bernardi提出的Full Couterpoise方法消除了计算中的基组重叠误差(BSSE),得出了该体系的各向异性相互作用势的单点能数据,通过拟合得到了较为准确的He-O2体系相互作用势的解析表达式.采用精确度较高的密耦(Close-Coupling)近似方法,计算了He-O2碰撞体系的碰撞激发微分截面,计算得到的微分截面数据与实验值符合较好,并得出了不同碰撞能量时He原子与O2分子的碰撞的微分截面的规律.     

NaB2和Na2B的结构与解析势能函数

使用Gaussian03程序包,采用单双取代耦合簇(CCSD)方法,选择基组6-311+g(2df)、6-311++g(3df,3pd)分别对B2及NaB和Na2分子的基态进行优化计算,运用最小二乘法拟合得到B2、NaB和Na2分子势能函数,给出与实验值符合很好的光谱常数;选择6-31++g（3df,3pd）基组,对NaB2和Na2B分子的结构进行优化计算.在此基础上,采用多体项展式法,得到NaB2和Na2B分子基态解析势能函数.势能面静态特征表明,该势能函数准确再现了NaB2和Na2B分子基态平衡结构.     

D+HS反应的含时量子动力学研究

利用含时波包方法对D+HS交换和抽取通道进行量子动力学研究,动力学计算中所采用的势能面由高精度从头算能量点构建.在平动能0.0～2.0 eV区间内计算了反应物初始振转基态时的总反应几率和积分反应截面,并且计算了初始振动激发态对积分反应截面的影响.所有动力学计算均考虑了科里奥利耦合效应.在低平动能时抽取通道在反应中占主导地位,而交换通道在高平动能时占主导地位.在整个所研究的平能能区间内,反应物HS的振动激发对抽取和交换通道反应都有增强作用.