Theoretical study on structures and stability of triplet SiC<Subscript>3</Subscript>O isomers

Various levels of calculations are carried out~for exploring the potential energy surface (PES) of triplet SiC₃O, a molecule of potential interest in interstellar chemistry. A total of 38 isomers are located on the PES including chain-like, cyclic and cage-like structures, which are connected by 87 interconversion transition states at the DFT/B3LYP/6-311G(d) level. The structures of the most relevant isomers and transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311+G(2df) single-point energy calculations. At the QCISD level, the lowest lying isomer is a linear SiCCCO 1 (0.0 kcal/mol) with the ³ ∑ electronic state, which possesses great kinetic stability of 59.5 kcal/mol and predominant resonant structure . In addition, the bent isomers CSiCCO 2 (68.3 kcal/mol) and OSiCCC 5 (60.1 kcal/mol) with considerable kinetic stability are also predicted to be candidates for future experimental and astrophysical detection. The bond natures and possible formation pathways in interstellar space of the three stable isomers are discussed. The predicted structures and spectroscopic properties for the relevant isomers are expected to be informative for the identification of SiC₃O and even larger SiC _n O species in laboratory and interstellar medium. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

B4O分子异构化稳定性的理论研究

采用CCSD(T)/6-311+G(2df)//B3LYP/6-311+G(d)方法, 系统研究了B₄O体系各个异构体的结构和能量, 以及重要异构体的解离和异构化稳定性. 结果表明, 单态平面三角形含-BO单元的异构体cB₃-BO ¹1能量最低, 其次是带状的异构体B₄O ¹2(10.9 kJ/mol), 并且¹1和¹2结构都具有良好的动力学稳定性. 因此对于B₄O体系, ¹1和¹2都是有可能存在的. 而文献报道的三态直线型结构BBBBO(146.0 kJ/mol)的能量比异构体¹1和¹2高得多.     

Structure and Stability of Interstellar Molecule C_3S

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Theoretical Studies on Structure,Isomerization, and Stability of [Si,O, S]

The structures, energetics, and isomerization of a possible interstellar [Si, O, S] system were explored at the CCSD(T)/aug-cc-pVQZ//CCSD(T)/aug-cc-pVTZ level. On the schemaitc potential energy surface(PES), we found that silicon oxysulfide(OSiS) produced in laboratory is the global minimum. An analysis of the Wiberg bond index(WBI), bond order and the bond length, shows that silicon oxysulfide contains SiO and SiS double bonds in accordance with the results of Schn?ckel. Besides silicon oxysulfide, another interesting cyclic minimum(c-SiOS) was found to have a very high kinetic stability stabilized by the least barrier of 120.9 kJ/mol. In light of the fact that no cyclic sulfide-containing species has been detected in space, c-SiOS could be a very promising candidate. The presented results might provide useful information on detected interstellar molecules O=Si=S and c-SiOS.     

Theoretical study on the potential energy surface of NC<Subscript>3</Subscript>P isomers

Density functional theory (DFT) calculations have been used to study the isomerization process in the NC₃P system. At the DFT/B3LYP/6-311G(d) level, 28 triplet and 28 singlet minima were obtained on their respective potential energy surfaces. The linear triplet ³NCCCP is the lowest-energy structure among the isomers. On the triplet PES, only linear isomers ³NCCCP, ³CNCCP, ³CCCNP, and ³CCNCP possess great kinetic and thermodynamic stabilities to exist under low-temperature conditions (such as in the dense interstellar clouds). At the same time, one chain-like and four three-membered-ring isomers on the singlet PES have been located with high kinetic and thermodynamic stabilities. Further CCSD(T)/6-311G(2df)//QCISD/6-311G(d), CCSD(T)/cc-pVTZ//DFT/B3LYP/cc-pVTZ, and CASPT2(14,12)/cc-pVQZ//CASSCF(14,12)/cc-p VQZ calculations are performed on the structures, frequencies, and energies of the relevant species. The bonding natures were analyzed and the results were compared with the analogous NC₃N and NC₂P molecules so as to aid their future experimental or astrophysical detection.     

O+HCNO反应势能面的理论研究

采用CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE方法对反应O＋HCNO进行了研究. 通过反应势能面揭示了该反应的机理, 通过H或O迁移等多步反应路径得到3种产物, 其中, P1(HCO+NO)为主要产物, P2(HNO+CO)和P3(NCO+OH)为次要产物. 为进一步实验研究提供了参考.     

HPOS体系异构体结构与稳定性

在MP2／6－311＋＋G(d,p)和QCISD（T）／6－311＋＋G（3df,2p)（单点）水 平下计算得到了HPOS体系势能面上18个异构体和25个过渡态及解离碎片等驻点，并 分析了这些异构体的结构及异构化过程，讨论了可能的解离方式。在得到的异构体 中，有8个异构体是动力学较稳定的，它们是dis-HOPS,trans-HOPS,trans-HSPO, cis-HSPO,HP(O)S(Cs),trans-HPSO,cis-HPSO和HP（O）S（C1）。这些异构体在实 验中应该可以观测到。理论研究表明，P与S原子较强的超价能力在降低异构体能量 ，提高异构体动力学稳定性方面起到了关键的作用。得到的计算结果与HPO2， HPS2，HNOS等价电子相同的体系进行了比较。     

Theoretical study on structures and stability of SiCP2 isomers

The structures, energetics, spectral parameters and stability of the singlet SiCP₂ isomers are explored at the density functional theory and ab initio levels. Eight isomers connected by ten interconversion transition states are located at the CCSD(T)/6-311G(2d)//B3LYP/6-311G(d)level. The kinetically stable isomers and their relevant interconversion transition states are further refined at CCSD(T)/6-311+G(2df)//QCISD/6-311G(d) level. At QCISD/6-311G(d) level, one four-membered ring isomer cSiPCP and two linear structures PSiCP, SiCPP possess considerable kinetic stability (more than 15 kcal/mol). The valence bond structures of three kinetically stable SiCP₂ isomers are analyzed. The similarities and discrepancies in structure, energy and stability between SiCP₂ and its analogous C₂P₂, Si₂P₂, SiCN₂ and CSiNP molecules are also discussed. The predicted structures and spectroscopic properties are expected to be informative for the identification of the SiCP₂ in the laboratory and space.     

Radical–molecule reaction CH<Subscript>2</Subscript>Cl + NO<Subscript>2</Subscript>: a mechanistic study

The radical–molecule reaction mechanism of CH₂Cl with NO₂ has been explored theoretically at the B3LYP/6–311G(d,p) and MC–QCISD (single-point) levels of theory. Our results indicate that the title reaction proceeds mostly through singlet pathways, less go through triplet pathways. The initial association between CH₂Cl and NO₂ is found to be the carbon-to-nitrogen attack forming the adduct a H₂ClCNO₂ with no barrier, followed by isomerization to b ₁ H₂ClCONO-trans which can easily convert to b ₂ H₂ClCONO-cis. Subsequently, the most feasible pathway is the C–Cl and O–N bonds cleavage along with the N–Cl bond formation of b (b ₁ , b ₂ ) leading to product P ₁ CH₂O + ClNO, which can further dissociate to give P ₅ CH₂O + Cl + NO. The second competitive pathway is the 1,3-H-shift associated with O–N bond rupture of b ₁ to form P ₂ CHClO + HNO. Because the intermediates and transition states involved in the above two favorable channels all lie below the reactants, the CH₂Cl+NO₂ reaction is expected to be rapid, as is confirmed by experiment. The present results can lead us to understand deeply the mechanism of the title reaction and may be helpful for further experimental investigation of the reaction.     

Theoretical study on the structures, isomerization and stability of SiC3H isomers

The calculations of the geometry optimizations, energies, dipole moments, vibrational spectra, rotational constants, and isomerization of doublet SiC₃H species were performed using density functional theory and ab initio methods. Four types of isomers, a total of 18 minima, connected by 16 interconversion transition states, were located on the potential energy surface (PES) at the B3LYP/6-311G (d, p) level. More accurate energies were obtained at the CCSD(T)/6-311G(2df, 2p), and G3(MP2) levels. With the highest isomerization barrier, the lowest lying structure, linear A1 possesses the largest kinetic stability. Besides, the isomerization barriers of A2, A4, C2, F1, F4 and F5 are over 10 kcal/mol, and these isomers are also considered to be higher kinetically stable. Other isomers cannot be kinetically stabilized with considerably low isomerization barriers. Investigation on the bonding properties and the computations of vibrational spectra, dipole moments, and rotational constants for SiC₃H isomers are helpful for understanding their structures and also valuable for their detections in the interstellar space and laboratory.     

CFCl3的理论和紫外光电子能谱研究

采用紫外光电子能谱(PES)和量子化学方法,研究了以CFCl3化合物为代表的系列化合物(CFCl3、CF2Cl2、CF3Cl、CCl4)不同离子态的电子结构和性质。结果表明,四种化合物CF3Cl、CF2Cl2、CFCl3、CCl4的第一电离能依次下降。结合从头算自洽场分子轨道(abinitioSCFMO)和外壳层格林函数法(OVGF)计算对化合物的PES进行了分析和指认,表明化合物的外层轨道中Cl的孤对电子成分对电离能存在明显的影响;外层格林函数法计算得到电离能与实验吻合很好;同时发现在外壳层格林函数法计算结果中由于考虑相关能,得到的分子轨道存在能级顺序的交错。     

Die Kristallstrukturen der Kupfer(II)-oxo-selenite Cu2O(SeO3) (kubisch und monoklin) und Cu4O(SeO3)3 (monoklin und triklin)

Syntheses within the system CuO-SeO₂-H₂O revealed four copper(II)-oxo-selenites. The crystal structures of these compounds were determined by single crystal X-ray techniques. Chemical formulae, lattice parameters and space groups are: Cu₂O(SeO₃)-I [a=8.925 (1) Å, P2₁3], Cu₂O(SeO₃)-II [a=6.987 (5) Å,b=5.953 (4) Å,c=8.429 (6) Å, =92.17 (3)°, P2₁/n], Cu₄O(SeO₃)₃-I [a=15.990 (8) Å,b=13.518 (8) Å,c=17.745 (12) Å, =90.49 (5)°, P2₁/a], and Cu₄O(SeO₃)₃-II [a=7.992 (6) Å,b=8.141 (6) Å,c=8.391 (6) Å, =77.34 (3)°, =65.56 (3)°, =81.36 (3)°, ].All the Cu atoms are-with one exception-[4], [4+1], and [4+2] coordinated by O atoms. The four nearest O atoms are more or less distorted square planar arranged. Within the CuO₄ squares the Cu-O bond lengths are significantly shorter for the [4] coordinated O atoms as compared with those of the [4+1] and [4+2] coordinated Cu atoms. The exception in the coordination of the Cu atoms is the Cu(1) atom in Cu₂O(SeO₃)-I with the site symmetry 3, which is trigonal dipyramidal [5] coordinated. A common feature of these four crystal structures is, that O atoms outside the SeO₃ groups are tetrahedrally coordinated by four Cu(II) atoms. The Se atoms are as usual [3] coordinated, building up SeO₃ pyramids. In all these four compounds the copper-oxygen polyhedra are combined to a three-dimensional network.

     

Electronic structures of the S2O and S3 isomers: an ab initio CI study

The electronic structures of the S₂O and S₃ isomers have been dealt with by the multireference double-excitation (MRD) configuration-interaction (CI) calculations, using contracted [5s3p1d] and [4s2p1d] basis functions for the S and O atoms, respectively. The ground-state geometries for the SOS (symmetric chain), S₂O (symmetric ring) and SSO (unsymmetric chain) are optimized, and their vertical singlet excitation energies are calculated. It is found that SSO is the most stable of the three isomers and that the ground state (¹A₁) of the S₂O (ring) is correlated with the excited states of SOS (2¹A₁) and SSO (3¹A). The chain and ring isomers of S₃ have been treated in a similar manner. Energetics for the ring closure of the O₃, SO₂, SSO and S₃ chain molecules are discussed on a unified ground.Dedicated to Professor J. Koutecký on the occasion of his 65th birthdayPresented at the 5th International Congress on Quantum Chemistry, Montréal, August 1985     

Dissociation and IVR pathways for the CF3H(H2O)3 cluster

Classical trajectory simulations are used to study the intramolecular dynamics of isolated CF₃H and the CF₃H(H₂O)₃ cluster, by either exciting the CH stretch local mode to then=6 level or by adding an equivalent amount of energy to an OH stretch normal mode. Energy transfer from the CH local mode is statistically the same for CF₃H(H₂O)₃ as for isolated CF₃H, and agrees with previous experimental studies. Clusters excited with 6 quanta in the CH local mode are remarkably stable. Though the CF₃H-(H₂O)₃ intermolecular potential is only 1.5 kcal/mol, only 1 of 26 clusters excited with 6 quanta in the CH local mode dissociate within 10 ps. The absorption linewidth for the CH local mode in CF₃H(H₂O)₃ is related to IVR within CF₃H and not to the unimolecular lifetime of the cluster. When an OH stretch normal mode of the cluster is excited, energy transfer to CF₃H is negligible and nearly one half of the clusters dissociate within 10 ps.     

Theoretical study on the vibrational structure of S0 thiophosgene from the origin to dissociation

In this work, using our vibrational variational calculation method and a recently derived refined quartic potential energy surface for S₀ thiophosgene, we have carried out large scale vibrational calculations to analyze the vibrational structure of this electronic state in the whole range of vibrational excitation energies down from the origin and up to the dissociation limit (at ↼20,000 cm^↙1). In the lower excited vibrational range we have achieved satisfactory coincidence of calculated to experimentally measured frequencies, while at the higher vibrational excitations our main objective has been to estimate what part of the available vibrational level density is effectively involved into the vibrational mixing and IVR. The results from our calculations have been compared to the available experimentally obtained dataset (obtained from synchrotron IR, SEP and LIF spectra) as well as to conclusions from the analyses by other authors using local coupling models.     

HAsS2异构体结构与稳定性

在MP2/6-311++G(d,p)和QCISD(t)/6-311++G(3df,2p)(单点)水平下计算得到9个异构体和10个过渡态的HAsS₂体系势能面.异构体cis-HSAsS(E1)的能量最低,其次是trans-HSAsS(E2)、具有AsSS三元环的立体HAs(S)S(C_{s,E3)和HAs(S)S(C2v,E4)结构的异构体,能量分别比cis-HSAsS高1.46,60.78和93.63kJ/mol.根据体系的势能面,异构体E1,E2,E3和E4具有一定的动力学稳定性.AsH和S2第一步反应产物将会异构化为具有较高动力学稳定性的异构体E3,而SH和AsS第一步反应产物将会异构化为E1.计算结果与HNO2,HNS2,HPO2,HPS2和HAsO2等价电子相同的分子的势能面进行了比较.}     

H+HCNO反应势能面的理论研究

在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPVE水平下, 对反应H＋HCNO进行了研究. 建立了反应势能面, 揭示了该反应的反应机理, 通过H迁移、N—O键或C—N键断裂等多步反应, 得到4种产物, 其中最主要产物为P1(HCN+OH).     

Theoretical Study on the Structures and Stability of Isomers and Complex of[Si,C,O,O] Sytem

A detailed singlet potential energy surface(PES) of [Si,C,O,O] system including a van der Waals (vdW) comples SiO……CO2,eight isomers,and twelve transiton states is investigated by MP2 and QCISD(T) (single-point)methods.At the final QCISD(T)/6-311 G(2df)//MP2/6-311G(d) level with zero-point energy included,the complex SiO……CO is found to be thermodynamically and kinetically the most stable species.Although eight ismoers are located as local energy minima,they are rather unstable toward isomerization to the dissociation fragments or comples.For the reaction of silocon atoms with carbon dioxide,two competitive reaction channels are found,and the primary pathway,which leads to the products of SiO and CO fragments,is the direct oxygen-abstraction process from carbon dioxide by silicon atom with a41.16 kJ/mol reaction barrier height.Our predications are in good agreement with previous experimental and theoretical studies.     

Theoretical Study on the Structures and Stability of Isomers and Complex of [Si, C, O, O] System

Introduction[Si,C ,O ,O]systemhasattractedmuchattentioninthefieldsofchemistryandmaterials1 3becauseofthefollow ingseveralcauses .First,theinterestisthepotentialimpor tanceininterstellarspace .Heretofore ,SiC ,SiOandCOhavebeendetectedwithintheinterstellarmediumformanyyears,butno [Si,C ,O ,O]isomerswereobservedinthenebulae .FormanySi containingsystemshavebeenstudiedexperimentallyandtheoretically ,4 8andinviewofthepossibleexistenceofthe [Si,C ,O ,O]radicalininterstellarspace ,weselectthe…