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The potential-energy surface of the interstellar molecule C[sub 4]N is explored at the B3LYP/6-311G(d) level of theory. Thirteen isomers including the linear, three-membered ring, four-membered ring, A-like, Y-like, and cage-like structures are located as minima connected by 23 interconversion transition states. The structures of the most relevant isomers and transition states are further optimized at the QCISD/6-311G(d) level followed by single-point energy calculations at the MP4SDTQ, CCSD(T), and QCISD(T) levels with the 6-311G(2df) basis set. At the CCSD(T)/6-311G(2df)//QCISD/6-311G(d) level, the lowest-lying isomer is a linear structure CCCCN 1 followed by a CCC three-membered ring structure 4 with exocyclic CCN bonding that lies only 2.8 kcal/mol higher. The third and fourth low-lying isomers possess a CCC three-membered ring structure 5 with exocyclic CNC bonding at 21.4 kcal/mol and a linear structure CCCNC 2 at 23.4 kcal/mol, respectively. All the four isomers 1, 2, 4, and 5 and another high-lying isomer 3 with a linear CCNCC structure at 62.5 kcal/mol are shown to have considerable kinetic stability towards isomerization and dissociation. Thus, all the five isomers may be experimentally observable. Possible formation of these five stable C[sub 4]N isomers in interstellar space is discussed. Finally, our calculations show that the Møller-Plesset methods fail to predict even qualitatively the energetic properties between the four low-lying isomers 1, 2, 4, and 5, in comparison with the QCISD and CCSD results. This paper indicates that C[sub 4]N may be the first interstellar molecule with stable low-lying cyclic isomers among the C[sub n]N radical series to be detectable in near future. The results presented in this paper may provide useful information for future laboratory and interstellar identification of various C[sub 4]N isomers. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Three-dimensional potential energy surfaces (PESs) have been computed, and numerically fitted, for the ground states of CH system, which are of importance for the smallest carbon cluster, dicarbon (C) and dynamical study of the H-CC dissociation reaction. An accurate and over larger region of configuration space PES are produced. The potential shown that the linear dissociation path is the favorite for H-CC. Graphical abstract: [ABSTRACT FROM AUTHOR]

The mechanism and kinetics of the radical C + CH reaction have been investigated theoretically by direct ab initio kinetics over a wide temperature range. The potential energy surfaces have been constructed at the CCSD(T)/B3//UMP2/B1 levels of theory. The electron transfer was also analyzed by quasi-restricted orbital (QRO) in detail. It was shown that all these channels proceed exclusively via hydrogen abstraction. The overall ICVT/SCT rate constants are in agreement with the available experimental results. The prediction shows that the secondary hydrogen of CH abstraction by C radical is the major pathway at low temperatures (below 700 K), while as the temperature increases, the primary hydrogen of CH abstraction becomes more important and more favorable. A negative temperature dependence of the rate constants for the reaction of C + CH was observed. The three-( k) and four-parameter ( k) rate-temperature expressions were also provided within 243-2000 K to facilitate future experimental studies. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The hydrogen abstraction of CH3OH by C2 (A3Π u ) has been investigated by direct ab initio dynamics over a wide temperature range 200–3000 K. The potential energy surfaces (PESs) have been constructed at the UCCSD(T)/aug-cc-pVTZ//UMP2/6-311++G(d,p) levels of theory. Two different hydrogen abstractions on the methyl and hydroxyl sites of methanol are considered. For the methyl H-abstraction, it is essentially a hydrogen atom transfer (HAT), whereas the hydroxyl site H-abstraction is better described as a proton coupled electron transfer (PCET) according to the Natural Bond Orbital (NBO) analysis. The results suggest that the methyl site reaction is dominant, and the calculated rate constants are roughly consistent with available experimental values. On the other hand, the temperature dependence of deuterium kinetic isotope effects (KIEs) analysis reveals a substantial normal isotope effect in the methyl H-abstraction process, while normal and inverse KIEs coexist in the hydroxyl H-abstraction channel. Furthermore, the three and four–parameter expressions of Arrhenius rate constants are also provided within 200–3000 K. [ABSTRACT FROM AUTHOR]

Abstract: The structures, energetics, spectroscopies, and isomerization of the doublet Si2PO radical are explored at various levels. At the UB3LYP/6-311+G(2df) level, a total of 12 minimum isomers and 15 interconversion transition states are located. Four cyclic isomers are found to be thermodynamically and kinetically stable at the higher UCCSD(T)/6-311++G(2df)//UM062x/6-311+G(2df)+ZPVE and may be experimentally or astrophysically observable. The lowest-lying isomer 1 c-SiOSiP (2B2) (0.0kcal/mol) corresponds to a rhomboidal-type structure similar to the global state of Si2NO, followed by another three-membered ring isomer 3 O-cSiSiP (2A′) (23.1kcal/mol) which is similar to the global state of [Si, C, P, O]. Another two stable isomers are the three-membered ring isomers 11 P-cSiSiO (35.0kcal/mol) and 6 O-cPSiSi (47.5kcal/mol), respectively. The bonding nature of the four isomers is analyzed. Meanwhile, the calculated results are compared with its analogs SiCPO, Si2NO, and Si2PS. Implications in the laboratory and interstellar space are also discussed. The predicted structures and spectroscopic properties are expected to be informative for the identification of Si2PO in the laboratory and space. [ABSTRACT FROM AUTHOR]

A direct ab initio dynamics method is used to investigate the hydrogen-abstraction reaction of H2CO with NCO. The potential energy surface information is obtained at the MP2/6-311G(d,p) level. More accurate single-point energy is refined at the G3(MP2)//MP2/6-311G(d,p) level. Furthermore, the rate constants of reaction H2CO + NCO are evaluated by using the canonical variational transition state theory with small-curvature tunneling contributions over a wide temperature range of 200–2000 K. The calculated reaction enthalpy and rate constants are in good agreement with the available experimental values. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 394–400, 2009 [ABSTRACT FROM AUTHOR]

At various levels of theory, singlet and triplet potential energy surfaces (PESs) of Si2CO, which has been studied using matrix isolation infrared spectroscopy, are investigated in detail. A total of 30 isomers and 38 interconversion transition states are obtained at the B3LYP/6-311G(d) level. At the higher CCSD(T)/6-311+G(2d)//QCISD/6-311G(2d)+ZPVE level, the global minimum 11 (0.0 kcal/mol) corresponds to a three-membered ring singlet O-cCSiSi (1A′). On the singlet PES, the species 12 (0.2 kcal/mol) is a bent SiCSiO structure with a 1A′ electronic state, followed by a three-membered ring isomer Si-cCSiO (1A′) 13 (23.1 kcal/mol) and a linear SiCOSi 14 (1Σ+) (38.6 kcal/mol). The isomers 11, 12, 13, and 14 possess not only high thermodynamic stabilities, but also high kinetic stabilities. On the triplet PES, two isomers 31 (3B2) (18.8 kcal/mol) and 37 (3A″) (23.3 kcal/mol) also have high thermodynamic and kinetic stabilities. The bonding natures of the relevant species are analyzed. The similarities and differences between C3O, C3S, SiC2O, and SiC2S are discussed. The present results are also expected to be useful for understanding the initial growing step of the CO-doped Si vaporization processes. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

The reaction of N (2D) radical with NO2 molecule has been studied theoretically using density functional theory and ab initio quantum chemistry method. Singlet electronic state [N2O2] potential energy surfaces (PES) are calculated at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311+G(d) + ZPE and G3B3 levels of theory. All the involved transition states for generation of (2NO) and (O2 + N2) lie much lower than the reactants. Thus, the novel reaction N + NO2 can proceed effectively even at low temperatures and it is expected to play a role in both combustion and interstellar processes. On the basis of the analysis of the kinetics of all pathways through which the reactions proceed, we expect that the competitive power of reaction pathways may vary with experimental conditions for the title reaction. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

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-pVQZ 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. [ABSTRACT FROM AUTHOR]

The structures, spectroscopies, and stabilities of the doublet Si2NO radical are explored at the density functional theory (DFT) and ab initio levels. Seventeen isomers are located, connected by 26 interconversion transition states. At the CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, three low-lying isomers are predicted, that is, one bent species SiNSiO 3 (5.1 kcal/mol) containing the important Si&tbond;N triple bonding and two four-membered ring isomers including cyclic cSiNSiO 1 (0.0) with Si&bond;Si cross-bonding with C2v symmetry and puckered cSiNSiO 1′ (11.9) with divalent carbene character. Three low-lying isomers 1, 1′, and 3 have reasonable kinetic stabilities and might be observable either experimentally or astrophysically. The possible formation strategies of 1, 1′, and 3 in laboratory and in space are discussed in detail. The calculated vibrational frequencies and possible formation processes of 3 are consistent with recent experimental observations. In light of the fact that no cyclic nitrogen-containing species have been detected in space, two cyclic isomers 1 and 1′ could be promising candidates. Furthermore, the bonding nature of three isomers 1, 1′, and 3 is analyzed. The calculated results are also compared with those of the analogue C2NO radical. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [ABSTRACT FROM AUTHOR]

Abstract: The DFT/B3LYP/6-311G(d) and CCSD(T)/6-311G(2df) (single-point) methods have been used to investigate the potential energy surface of SiC2O. A total of 11 isomers are located, which are connected by 13 interconversion transition states. The global minimum is the linear SiCCO with 1Σ+ electronic state whose structure can be described as cumulenic double bonding form :Sih name="dbnd" />CThe isomer O-cSiCC possessing SiCC three-membered ring with an exocyclic OSi bond also shows considerable stability. Both SiCCO and O-cSiCC are kinetically stable towards isomerization and dissociation. Further calculations are performed at the CCSD(T)/6-311G(2df)//QCISD/6-311G(2d) level to obtain more reliable energies, geometrical parameters, harmonic vibrational frequencies and infrared intensities of the isomers. The energies and geometrical parameters are also calculated with the CASPT2//CASSCF methods. [Copyright &y& Elsevier]

Abstract: The reaction of linear form carbon cluster C3 molecules in their 1Σ ground state with NO (X2Π) radicals is explored theoretically to investigate the formation of hitherto undetected NCCCO molecules in the interstellar medium via a neutral-neutral reaction. The doublet potential energy surface is worked out by the ab initio MO calculations at the CCSD(T)/cc-pVTZ//B3LYP/6-311G(d,p)+ZPE level of theory. It is shown that the main pathway of the C3(1Σ)+NO(X2Π) reaction involves the N-atom of NO attacking the side C-atom of the 1C3 molecule first to form the adduct CCCNO, followed by the N-shift to give I6 CCNCO, and then to the main products P1 (CCN+CO). Alternatively, I6 can be converted via the N-shift again to I9 (CN)CCO, and then it leads to the minor products P2 (CNC+CO) and P3 NCCCO. Since the three pathways have zero threshold energy and proceed via strongly bound energized complexes, they should possess the character of negative temperature dependence, and might be quite rapid even at very low temperature. The reaction represents facile neutral-neutral pathways to produce hitherto undetected CCN, CNC and NCCCO molecules in interstellar environments. [Copyright &y& Elsevier]

The potential energy surface of complex doublet for the HCCCOOO system is investigated in this paper at the hybrid density functional B3LYP and CCSD(T) (single-point) levels with 6-311G(d,p) basis set in order to find out the reaction mechanism of the radical HCCCO with oxygen. Nineteen minimum isomers and 22 transition states are located and a variety of possible reaction pathways are probed. In this article, we discussed five products P1 HCCO+CO2, P2 HCO+2CO, P3 HCO2+C2O, P4 H+3CO and P5 H+CO2+C2O. The reaction pathway leading to the major HCCO+CO2 product is as following: HCCCO+O2→a3→TSa3/b3→b3→TSb3/b4→b4→TSb4/p1, in which the rate-determining step is isomer a3 overcomes the barrier (27 kcal/mol) to form the isomer b3. It is an interesting process for it keeps the Cs symmetry in the reaction. Another important pathway leading to HCO+2CO product is the formation of d1 isomer. Once the structure of d1 is formed, it will directly dissociate to g+CO. Calculation on these would be useful for our understanding about the reactions of HCCCO+O2. [Copyright &y& Elsevier]

In the present study, the reaction mechanism of NCS+NO2 on the singlet potential energy surface is studied using the MP2/6-311G(d,p) level of theory. It is shown that the pathway (1) is the major pathway, and the pathways (2) and (3) are the minor pathways in the singlet potential energy surface. The major pathway (1), involving the barrierless entrance to the first adduct isomer O(O)NNCS and tight transition states to the products N2O and OCS, is in good agreement with the experimentally observed negative temperature dependence of rate constants. The energies of the stationary points are refined using a multi-level method. [Copyright &y& Elsevier]

Abstract: The mechanisms of the reaction of ozone with cis- and trans-1,3-butadiene are investigated at the B3LYP/6–311G(d,p) and CCSD(T)/6–311G(d,p) (single-point) computational levels. Both reactions are associated with the cycloaddition – elimination mechanism. In the O3 + cis-1,3-butadiene reaction, the initial cycloaddition product 3 will eventually lead to four most favorable products P1 (cis–trans-CH2CHCHOO+H2CO), P2 (cis-CH2CHCHO+H2CO2), P3 (trans-CH2CHCHO+H2CO2) and P4 (trans–trans-CH2CHCHOO+H2CO) which have the same calculated barrier 3.0kcal/mol with respect to the reactant (O3 + cis-1,3-butadiene). In the O3 + trans-1,3-butadiene reaction, there are two initial cycloaddition products 4 and 8, which will lead to six favorable products P1 (cis–trans-CH2CHCHOO+H2CO), P2 (cis-CH2CHCHO+H2CO2), P3 (trans-CH2CHCHO+H2CO2), P4 (trans–trans-CH2CHCHOO+H2CO), P7 (trans–cis-CH2CHCHOO+H2CO) and P8 (cis–cis-CH2CHCHOO+H2CO) with similar calculated barriers ranging from 4.7 to 5.4kcal/mol. The present paper will enrich our understanding of the chemistry of ozone towards other unsaturated hydrocarbons. [Copyright &y& Elsevier]

Abstract: The ion-molecule reaction mechanism of SF+ with PSCl3 is explored theoretically at the CCSD(T)/6-311+G(2d) level using the B3LYP/6-311G(d), and B3LYP/6-311++G(d) geometries. Various possible reaction pathways are probed. It is shown that eight dissociation products P1 (S2F+ +PCl3), P2 (S2Cl+ +PFCl2), P3 (SPCl2 + +FSCl), P4 (PCl2 + +FSSCl), P5 (S2 + +PFCl3), P6 (FSPCl+ +SCl2), P7 (FSPClS+ +Cl2) and P8 (PSCl3 + +SF) are both thermodynamically and kinetically accessible. Among the eight dissociation products, P8 is the most favorable product with the largest yields, whereas P1 is much less competitive followed by the least feasible products P2 and P3 . The remaining products, P4 , P5 , P6 , and P7 may have negligible yields. Significant discrepancies on the product distributions are found between our calculated results and previous experimental observations. Therefore, future experimental reinvestigation on the SF+ +PSCl3 reaction is desirable to clarify the mechanism of the title reaction. The present work may be helpful for understanding the analogous ion-molecule reactions in gas phase. [Copyright &y& Elsevier]

Abstract: A detailed theoretical study is performed at the UMP2/6-311++G(d,p) and CCSD(T)/aug-cc-pVTZ (single-point) levels in order to explore the mechanism of the reaction between cis-CH3ONO/trans-CH3ONO and H. For cis-CH3ONO+H reaction, six products are obtained. P1 (CH3OH+NO), and P6 (CH3O+HNO) are the most feasible products. P3 (CH3 + trans-HONO), P4 (CH3 + cis-HONO), and P5 (cis-CH2ONO+H2) are the second feasible products, followed by the least feasible product P2 (CH4 +ONO). For trans-CH3ONO+H reaction, five dissociation products are obtained. P1 (CH3OH+NO), P6 (CH3O+HNO), and P7 (trans-CH2ONO+H2) are the most feasible products, the lesser followed competitive product is P4 (CH3 + cis-HONO), while P2 (CH4 +ONO) is even much less feasible. Our theoretical results are in consistent with the available experiments. Because the rate-determining transition states involved in the feasible pathways lie above the reactant R, the title reactions may be important at higher temperatures. The present paper may be helpful for modeling of methyl nitrite–hydrogen combustion chemistry. [Copyright &y& Elsevier]

Abstract: The reaction of atomic radical N (4S) with NO2 was explored theoretically using density functional, coupled cluster, and Møller–Plesset perturbation theory. The triplet electronic state potential energy surface (PES) was calculated at the G3B3 and CCSD(T)/cc-pVTZ//B3LYP/6-311+G(d,p) levels of theory. Various possible reaction pathways, including the N-adduct-O-shift and four-center ring formation-decomposition reactions, are considered. On the PES of the title reaction, it is shown that the most favorable pathway should be the atomic radical N attacking the N-atom of NO2 firstly to form the adduct 1 NN(OO), followed by one of the NO bonds breaking to give intermediate 2 NNOO, and then leading to the major products P2 (O2 +N2). As efficient routes to the reduction of NO2 to form N2 and O2 are sought, both kinetic and thermodynamic considerations support the viability of this channel. The transition states involved in the generation of products P1 (2NO), P2 (O2 +N2), and P3 (3O+N2O) lie much lower than the reactants. Thus, the novel reaction N+NO2 can proceed effectively even at low-temperature and it is expected to play an important role in both combustion and interstellar processes. The reaction heats of formation calculated are in good agreement with that obtained experimentally. [Copyright &y& Elsevier]

Abstract: The reaction of isocyanato radical, NCO (X2∏) with chlorine atom, Cl (2Pu) is investigated by ab initio quantum chemistry methods. The important triplet potential energy surfaces (PES) are calculated at the CCSD(T)/aug-cc-pVQZ//CCSD/6-311++G∗∗+ZPE levels. On the triplet PES of the title reaction, the most possible pathway is via 3TSR-1 forming the cis isomer 31, and then 31 can lead to the lower trans isomer 32 via transition state 3TS1-2, followed by the transition state 3TS2-P1 to get the important product P1 with larger exothermic. The other reaction pathways are less competitive due to thermodynamical or kinetic factors. The possible singlet–triplet intersystem crossing is also discussed. We expect this contribution can lead us to deeply understand the mechanism of the title reaction and may be helpful for the modeling of isocyanato radical-halogen combustion chemistry. [Copyright &y& Elsevier]

Abstract: The potential energy surface of the possible interstellar molecule Si2CS is investigated at the B3LYP/6-311G(d) level. Eight singlet isomers are located as energy minima and connected by fifteen transition states. Further calculations are performed using the Quadratic CI calculation including single and double substitutions (QCISD/6-311G(2d)) to get more reliable geometrical parameters, harmonic vibrational frequencies, and infrared intensities of the relevant structures. And at the higher (single point) CCSD(T)/6-311+G(2d)//QCISD/6-311G(2d)+ZPVE level, the global state (at 0.0kcal/mol) corresponds to a planar four-membered ring form. This is followed by the next most stable chain-like isomer SiCSiS (at 1.7kcal/mol higher the global state) and its geometries is very sensitive to electronic correlation effects. They represent not only high thermodynamic stabilities, but also high kinetic stabilities. These two isomers may be experimentally or astrophysically observable. Meanwhile, the calculated results are compared with the analogous species C3O, C3S, and SiC2S. [Copyright &y& Elsevier]

Abstract: The reaction of OH radical with nitrous acid HONO is investigated by ab initio quantum chemistry methods. The doublet potential energy surfaces are calculated at the CCSD(T)/aug-cc-pVDZ//UMP2/6-311++G(d,p) levels. Various possible reaction pathways are considered. Among them, the most feasible pathway should be the OH radical attacking on the hydrogen of cis-HONO to form a 6-member-ring complex C2 barrierlessly, followed by the indirect hydrogen abstraction transition state TSabsC2-C6I to form a weakly bound complex C6, giving rise to the educts P1 H2O+NO2. Because all of the complexes, transition state, and products involved in the feasible pathway lie below the reactants, the title reaction is expected to be rapid, which in good agreement experiment. The present study may be helpful for probing the mechanisms of the HONO reactions and understanding the atmospheric chemistry. [Copyright &y& Elsevier]

Abstract: The reactions of atomic radical F and Cl with acetylene have been studied theoretically using ab initio quantum chemistry methods and transition state theory. The doublet potential energy surfaces were calculated at the CCSD(T)/aug-cc-pVDZ//CCSD/6-31G(d,p), CCSD(T)/aug-cc-pVDZ//UMP2/6-311++G(d,p) and compound method Gaussian-3 levels. Two reaction mechanisms including the addition–elimination and the hydrogen abstraction reaction mechanisms are considered. In the addition–elimination reactions, the halogen atoms approach C2H2, perpendicular to the Cbond, forming the pre-reactive complex C1 at the reaction entrance. C1 transforms to intermediate isomer I1 via transition state TSC1/1 with a negative/small barrier for C2H2F/C2H2Cl system, which can proceed by further eliminating H atom endothermally. While the hydrogen abstraction reactions also involve C1 for the fluorine atom abstraction of hydrogen, yet the hydrogen abstraction by chlorine atom first forms a collinear hydrogen-bonded complex C2. The other reaction pathways on the doublet PES are less competitive due to thermodynamical or kinetic factors. According to our results, the presence of pre-reactive complexes indicates that the simple hydrogen abstraction and addition in the halogen atoms reaction with unsaturated hydrocarbon should be more complex. Furthermore, based on the analysis of the kinetics of all channels through which the addition and abstraction reactions proceed, we expect that the actual feasibility of the reaction channels may depend on the reaction conditions in the experiment. The present study may be helpful for probing the mechanisms of the title reactions and understanding the halogen chemistry. [Copyright &y& Elsevier]

Abstract: The reaction of F(2P) with nitrous acid has been studied theoretically using ab initio quantum chemistry methods and transition state theory. The potential energy surface was calculated at the CCSD(T)/cc-pVTZ and QCISD(T)/cc-pVTZ (single-point) levels using the UMP2/6-311++G(d,p) optimized structures. Various possible reaction pathways including the direct H-abstraction reaction and three kinds of addition reactions are considered. Among them, the most feasible pathway should be the F atom abstracting hydrogen of cis-HONO directly, leading to the products P1 HF+NO2. The other reaction pathways are less competitive due to thermodynamical or kinetic factors. Furthermore, our calculation results show that, in terms of potential energy surface, the title reaction involves all the main features of H+HONO reaction. However, the mechanisms of F with HONO are more complicated than those of H+HONO. The reaction heats of formation calculated are in good agreement with that obtained experimentally. It will provide useful information for understanding the mechanism of F atom reaction. [Copyright &y& Elsevier]

Abstract: The doublet potential energy surface (PES) for the reaction of CHCl− with CSO is explored at the B3LYP/6-311++G(d,p), B3LYP/6-311++G(3df,2p) and CCSD(T)/6-311++G(3df,2p) (single-point) levels. Various possible reaction pathways are probed. It is shown that the most favorable association between CHCl− and CSO is found to be middle-C attack forming CHClC(O)S− 1 with no barrier. Starting from 1, the most feasible pathway is the concerted S-shift along with Cl-extrusion of 1 to form product P2 (Cl− +SCHCO). The minor product channel is the concerted O-shift along with Cl-extrusion of 1 to generate product P1 (Cl− +OCHCS). Further conversions of P1 may form P6 (SCHCl− +CO). Because the isomers and transition states involved in the feasible pathways all lie below the reactant, the title reaction is expected to proceed very fast which is consistent with the measured large rate constant in experiment. Our calculated results may be helpful for understanding the mechanism of the title reaction. [Copyright &y& Elsevier]

Abstract: The reaction of NCO with CH3 is studied at B3LYP/6-11G(d,p) and CCSD(T)/6-311++G(3df,2pd) (single-point) levels. On the singlet potential energy surface (PES), the most feasible channel is direct radical–radical recombination leading to isomers OCNCH3 and NCOCH3. Further isomerization and dissociation of OCNCH3 and NCOCH3 to yield the dissociation products need to surmount the energy barrier at least 4.7kcal/mol with respect to reactant, which indicate that these processes are kinetically unfeasible at normal temperatures and may become feasible only at high temperatures. Compared with the singlet pathways, the triplet pathways may have less contribution to the title reaction. [Copyright &y& Elsevier]

Abstract: The structures, energetics, spectroscopies, and stabilities of the doublet Si2PS radical are explored at the density functional theory and ab initio levels. Fifteen minima including the chainlike, three-membered ring, four-membered ring, and cagelike structures are located connected by 24 interconversion transition states. The structures of the stable isomers and their relevant transition states are further optimized at the QCISD/6-311G(2d) level. At the CCSD(T)/6-311+G(2df)//DFT/B3LYP/6-311G(d)+ZPVE level, the global minimum is found to be a four-membered-ring cPSiSSi 10 (0.0kcal/mol) with a 2A′′ electronic state, whereas the cagelike isomer cagePSiSiS 15 (3.5kcal/mol), the three-membered-ring isomers S-cSiPSi 4 (12.1kcal/mol), and P-cSiSiS 5 (27.6kcal/mol) also possess considerable kinetic stabilities (more than 10.0kcal/mol). The bonding natures and structures of the four isomers 4, 5, 10, and 15 are analyzed. The calculated results are compared with those of the analogous molecules C2PS and SiCPS. [Copyright &y& Elsevier]

The potential energy surface of the F + CHFO reaction is investigated at the MP2/6-311+G(d,p), MP4SDQ/6-311G(d,p), and QCISD(T)/6-311+G(3df,2p) (single-point) levels to explore the reaction mechanism. Theoretical calculations suggest that the hydrogen abstraction by fluorine atom leading to the products HF and CFO is kinetically much more competitive than the addition process. Furthermore, the direct dynamics calculation of this hydrogen abstraction reaction is performed at the QCISD/6-311+G(3df,2p)//MP4SDQ/6-311G(d,p) level. The rate constants are evaluated by means of canonical variational transition-state theory (CVT) including small-curvature tunneling (SCT) correction over a range of temperatures 220–1500 K. Our results agree well with the available experimental data. [Copyright &y& Elsevier]

A detailed singlet potential energy surface (PES) of the CHOP system is investigated by means of MP2 and QCISD(T) methods. It is shown that the chainlike isomer HPCO is the most stable species followed by the chainlike HOCP and trans-HCPO, which are also considered as kinetically stable species, and may be experimentally observable. Furthermore, possible molecular dissociation channels are predicated and the result show that the direct dissociation of chainlike HPCO can efficiently proceed prior to almost all isomerizations, but the isomerizations of HOCP and trans-HCPO towards the lowest-lying HPCO are favorable in energy than their direct dissociations. [Copyright &y& Elsevier]

A singlet potential energy surface (PES) of the [Si,N,C,S]+ system is investigated by means of MP2 and QCISD(T) (single-point) methods. Four linear isomers of [Si,N,C,S]+ system are found to be kinetically stable and should be experimentally observable. The linear isomer SiNCS+ is the thermodynamically most stable, followed by SSiCN+, SSiNC+ and SiCNS+. No cyclic kinetically stable isomers are found. For the isomer SiNCS+, several isomerizations can very favorably compete with its direct dissociation, and thus, the very recent mass spectrometric experiment can reasonably be interpreted by analyzing the structures and bonding. [Copyright &y& Elsevier]