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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]

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: We performed a detailed theoretical study on the neutral, cationic and anionic [H,Si,C,N] potential energy surfaces (PESs) at the Gaussian-3//B3LYP/6-31G(d) level. The former four low-lying isomers HSiCN 1 1 (0.0kcal/mol), HSiNC 1 2 (2.4), cCHNSi 1 7 (4.6) and HCNSi 1 3 (28.7) each have considerable kinetic stability, which supports their experimental characterization. In addition, two singlet isomers HNCSi 1 5 (29.7) and cNHCSi 1 8 (33.7), and four triplet isomers HSiCN 3 1 (26.5), HSiNC 3 2 (35.8), HCNSi 3 3 (29.1) and HNCSi 3 5 (29.7) are found to have high kinetic stability. They are expected to be detectable under suitable conditions. On the doublet [H,Si,C,N]+ PES, the linear structure HCNSi+ 2 3 + (0.0kcal/mol) and HNCSi+ 2 5 + (8.6) are considerably more stable than HSiCN+ 2 1 + (37.2) and HSiNC+ 2 2 + (34.3), in contrast to the neutral [H,Si,C,N] PES. However, on the doublet anionic [H,Si,C,N]− PES, the isomers HSiCN− 2 1 − (0.0kcal/mol) and HSiNC− 2 2 − (10.4) are still the lower-lying isomers, similar to the neutral PES. Based on the [H,Si,C,N]0,± PESs, the electron ionization and capture stabilities of various [H,Si,C,N] species are discussed, which might give insight into their mass spectrometric characterization in future. Finally, the proton ionization values of the two known interstellar radicals SiCN and SiNC are found to be very high, showing the high possibility of the existence of the cationic [H,Si,C,N]+ species. [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]

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 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 15kcal/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. [Copyright &y& Elsevier]

Abstract: The structures, energetics, spectral parameters and stability of the doublet [Si, C, P, S] radical are explored at the density functional theory and ab initio levels. Sixteen isomers connected by 23 interconversion transition states are located on the PES. The structures of the stable isomers and their relevant 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/6-311G(d) level, the lowest-lying isomer is a bent SSiCP 1 (0.0kcal/mol) with considerable isomerization barriers (the lowest barrier is 12.6kcal/mol). In addition, the bent isomer SiCSP 5 (57.3kcal/mol) and the cyclic species S-cCSiP 6 (2.7kcal/mol) also possess considerable isomerization barriers (more than 10.0kcal/mol). The valence bond structures of the three isomers 1, 5 and 6 are analyzed. The calculated results are compared with those of analogous molecules C2PS and [Si, C, N, O]. Implications in laboratory and interstellar space are also discussed. [Copyright &y& Elsevier]

Abstract: The reaction of CN with HONO is explored theoretically using coupled cluster and Møller–Plesset perturbation theory. Various possible reaction pathways including the H-abstraction reactions and addition–isomerization–elimination reactions are considered. Because the rate-determining barrier in the most feasible pathway lies −4.92/−30.58kcal/mol (ΔE ‡/ΔG ‡) lower than reactants, the reaction is expected to be very rapid. Based on the analysis of the temperature influence of the reaction mechanism, we expect that the actual reaction mechanism may vary with experimental conditions. We expect this contribution can lead us to deeply understand the mechanism of the title reaction. [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 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: Although the rate constants of the C3H5+NO reaction were determined more than 20 years ago, no theoretical investigations have been reported up to now. In present paper, we performed a detailed mechanistic study on this reaction by constructing a singlet potential energy surface [C3H5NO] at the CCSD(T)/6-311G(d,p) //B3LYP/6-311G(d,p) level. The most favorable entrance channel is the direct radical–radical combination to form isomer H2CCHCH2NO m1 (−23.44kcal/mol). The calculated zero barrier is consistent with the determined high rate constant at room temperature. Except dissociation back to the reactants, the further conversion of m1 needs to overcome the transition states with energies being at least 23kcal/mol higher than the reactant. This is indicative of a distinct pressure dependence of the rate constants, which is also consistent with the experimental finding. The energetically very low-lying products P 1 CH2CHCN+H2O (−71.36kcal/mol), P 2 CH3CHO+HCN (−72.61kcal/mol) and P 3 CH3CHO+HNC (−57.55kcal/mol), however, cannot be reached kinetically. [Copyright &y& Elsevier]

Abstract: The structures, energetics, spectroscopies, and stabilities of the doublet PC2S radical are explored at density functional theory and ab initio levels. Seven minimum isomers are located connected by 20 interconversion transition states. At the CCSD(T)/6-311+G(2df)//QCISD/6-311G(d)+ZPVE level, the lowest-lying isomer is a linear form PCCS 1 whose structure mainly resonates between and with the former bearing somewhat more weight. The species 1 is predicted to possess great kinetic stability about 50kcal/mol. Additionally, two high-lying isomers, i.e. bent CCPS 2 (52.0) and bent CCPS 2′ (54.9), are also stabilized by the considerable barriers of 21.0 and 18.1kcal/mol, respectively. Interestingly, the isomers 2 and 2′ can be easily converted to each other, both of them could coexist. All the three isomers should be experimentally or astrophysically observable. The bonding natures of the isomers 1, 2, and 2′ are analyzed. Their molecular properties including adiabatic ionization potentials and adiabatic electronic affinities are determined at the higher levels G3//B3LYP and G3(MP2)//B3LYP. The calculated results are compared with those of the analogues NC2S and NC2O. Possible formation strategies of the isomers 1, 2, and 2′ in laboratory and in space are also discussed. The present PC2S work represents the first detailed potential energy survey of the PC n S (n>1) series and can provide useful information for future laboratory and interstellar identification of various PC2S isomers. [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]

Abstract: The doublet potential energy surface for the reactions 3NCN+NO, 3CNN+NO, 1NNO+CN and 2N3+CO is studied at the B3LYP/6-311G(d) and G2M(cc3) (single-point) levels of theory. For the reaction 3NCN+NO, the pathways 3NCN+NO⇌1 trans-ONNCN→2 cis-ONNCN→1NNO+CN and 3NCN+NO⇌2 cis-ONNCN→1NNO+CN are the major pathways. For the reaction 3CNN+NO, the pathway 3CNN+NO⇌3 trans-ONCNN→N2+2CNO is the major pathway. For the reaction 1NNO+CN, the pathways 1NNO+CN⇌2 cis-ONNCN→3NCN+NO and 1NNO+CN⇌2 cis-ONNCN→1 trans-ONNCN→3NCN+NO are the major pathways. For the reaction 2N3+CO, the pathways 2N3+CO⇌7 trans-OCNNN→N2+2NCO and 2N3+CO⇌7 trans-OCNNN→8 cis-OCNNN→N2+2NCO are the major pathways. In addition, the quartet potential energy surface for these reactions is also considered, but no favorable pathways can be found on it. [Copyright &y& Elsevier]

Abstract: A detailed isomerization reaction potential energy surface of HPS3 system is investigated by means of density functional method (B3LYP) employing 6-311++G(3df,3pd) basis set. The results indicate that planar isomer HSP(S)S is thermodynamically and kinetically the most stable species. Other several isomers, (cis–cis)-HSSPS (Cs), trans-HSP(S2) (C1), cis-HSP(S2) (Cs), and HP(S2)S (Cs), are also considered as kinetically stable isomers, and may be experimentally observable provided that precise precursors are available. Furthermore, the structural nature of these kinetically stable isomers are compared with its analogues and discussed by comparison with the standard bond length and bond angle parameters in relevant compounds. [Copyright &y& Elsevier]

Abstract: The complex triplet potential energy surface of the C2H3N system is investigated at the UB3LYP and CCSD(T) (single-point) levels in order to explore the possible reaction mechanism of C2H3 radical with N(4S). Eleven minimum isomers and 18 transition states are located. Possible energetically allowed reaction pathways leading to various low-lying dissociation products are obtained. Starting from the energy-rich reactant C2H3+N(4S), the first step is the attack of the N atom on the C atom having one H atom attached in C2H3 radical and form the intermediate C2H3N(1). The associated intermediate 1 can lead to product P1 CH2CN+H and P2 3CH2+3HCN by the cleavage of C–H bond and C–C bond, respectively. The most favorable pathway for the C2H3+N(4S) reaction is the channel leading to P1, which is preferred to that of P2 due to the comparative lower energy barrier. The formation of P3 3C2H2+3NH through hydrogen-abstraction mechanism is also feasible, especially at high temperature. The other pathways are less competitive comparatively. [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]