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  • 1
    Electronic Resource
    Electronic Resource
    Potential Energy Surface of the HNO + NO Reaction. An ab Initio Molecular Orbital Study (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 1900-1908 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100007a018
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  • 2
    Electronic Resource
    Electronic Resource
    Modification of the gaussian−2 theoretical model: The use of coupled-cluster energies, density-functional geometries, and frequencies (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 7414-7421 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A family of modified GAUSSIAN−2 (G2M) calculational schemes have been proposed, based on geometry optimization and vibrational frequency calculations using the hybrid density-functional approach, and electron correlation evaluation using the coupled-cluster methods. The most accurate model, called G2M(RCC), gives the average absolute deviation of calculated atomization energies from experiment for 32 first-row compounds of 0.88 kcal/mol. The other two methods, called G2M(RCC,MP2) and G2M(rcc,MP2), exhibit the average absolute deviations of 1.15 and 1.28 kcal/mol, respectively, and can be used for the calculations of molecules and radicals of larger sizes containing up to six to seven heavy atoms. The G2M(rcc,MP2) model demonstrates an accuracy comparable to that of G2(MP2) and requires less intensive computations than the latter. The preference of the G2M(RCC) methods over the original G2 is expected to be particularly significant for the open shell systems with large spin contamination. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470313
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  • 3
    Electronic Resource
    Electronic Resource
    An ab initio molecular orbital study of potential energy surface of the NH2+NO2 reaction (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5640-5649 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surface of the reaction of NH2 with NO2 has been studied at the QCISD(T)/6-311G(d,p)//MP2/6-311G(d,p)+ZPC[MP2/6-311G(d,p)] and GAUSSIAN−2 (G2) levels of calculation. The reaction is shown to give three different groups of products. H2NO+NO can be produced by two different channels: (i) the barrierless association of the reactants to form H2NNO2 1, followed by the nitro–nitrite rearrangement into H2NONO 3 and the ON bond scission and (ii) the association of H2N with ONO directly forming 3 without barrier, followed by the dissociation 3. The barrier for the nitro–nitrite rearrangement at the transition state (TS) 2, 31.2 kcal/mol with respect to 1, is 20.8 kcal/mol lower than the reactants at the best G2 level. The TS 2 is found to lie significantly lower and to have much tighter structure than those previously reported. The thermodynamically most stable N2O+H2O products can be formed from 1 by the complex mechanism (iii), involving 1,3-hydrogen shift from nitrogen to oxygen, rotation of the OH bond, H shift from one oxygen to another and migration of the second H atom from N to O leading to elimination of H2O. The rate-determining step is the 1,3-H shift at TS 4 which is 12.5 kcal/mol lower than NH2+NO2, but 8.3 kcal/mol higher than the barrier for the nitro–nitrite isomerization at TS 2 at the G2 level. N2+H2O2 cannot be formed in the reaction, but several channels are shown to produce N2+2OH. All of them have as the rate-determining step the second 1,3-hydrogen shift from nitrogen to oxygen at TS 11 or 16, lying by 6.9 kcal/mol higher than NH2+NO2, and are not expected to compete with the reaction mechanisms producing H2NO+NO and N2O+H2O. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470546
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical Study of the Gas-Phase Structure, Thermochemistry, and Decomposition Mechanisms of NH4NO2 and NH4N(NO2)2 (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 6842-6848 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100018a015
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  • 5
    Electronic Resource
    Electronic Resource
    Density functional study of the global potential energy surfaces of the [H,C,N,O]+ system in doublet and quartet states (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 3187-3205 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The global potential energy surfaces of the [H,C,N,O]+ system both in doublet and quartet states have been rather exhaustively studied with the B3LYP density functional method, with special attention to cover nearly all intermediate and transition states. Ionization potentials, energies of reactions, and proton affinities of fragments are calculated and compared with experiments to assess the reliability. In the doublet state, all six chain isomers and three cyclic structures exist, and rearrangements among them take place over high barriers mainly via the 1,3-H shift and chain–cycle transformation. Pathways for fragmentations of the isocyanic acid cation HNCO+ and fulminic acid cation HCNO+ have been identified and compared with the experiments. In the quartet state, there exist ion–molecule complexes between fragments as well as trans and cis forms of chain isomers and cyclic and open branched isomers, and the potential surfaces for interconversion and fragmentation are much more complicated. The potential energy profiles for the reaction of O+(4S)+HCN have been examined and pathways for production of experimentally observed HCN+, NO+, HCO+, and HOC+ have been identified to go through long-lived chain intermediates HCNO+ and HOCN+ and open branched intermediate NCHO+, while production of CO+ is more complicated. The crossing seam minimum with the doublet has been found right at the quartet intermediate HCNO+, and intersystem crossing and production of the stable doublet fulminic acid cation HCNO+ is likely to be an efficient process. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471834
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  • 6
    Electronic Resource
    Electronic Resource
    A density functional study of the global potential energy surfaces of the [H,C,N,O] system in singlet and triplet states (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 6439-6454 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Global potential energy surfaces (PESs) of the [H,C,N,O] system in singlet and triplet states have been investigated using the hybrid density functional B3LYP/6−311G(d,p) method. Isocyanic acid, HNCO 1, has been found to be the most stable isomer for both multiplicities. The adiabatic singlet–triplet splitting for 1 is 82.6 kcal/mol. In the singlet state, HNCO is energetically followed by cyanic acid, HOCN 2, 28.7 kcal/mol higher than 1, fulminic acid, HCNO 3 (67.9 kcal/mol), and isofulminic acid, HONC 4 (87.1 kcal/mol). In the triplet state, the branched NC(H)O isomer 37 is 0.3 kcal/mol higher than 31, followed by HOCN 32 (27.9 kcal/mol relative to triplet HNCO) and HCNO 33 (40.6 kcal/mol). The barriers for intramolecular rearrangements within singlet and triplet [H,C,N,O] system have been calculated to be high, and the isomerization processes in most cases are not expected to compete with fragmentations. Several minima on the singlet–triplet seam of crossing, relevant to the singlet [H,C,N,O] decomposition reactions, have also been found. The global features of the singlet and triplet PES have been applied to several important reactions, such as NH(3Σ−)+CO, thermal decomposition of HNCO, O(3P)+HCN, O(3P)+HNC, and CH(2Π)+NO(2Π). For these reactions, major product channels have been speculated and their activation energies have been reported. Adiabatic ionization potentials for singlet and triplet [H,C,N,O] have been found to be high, in the range of 180–270 kcal/mol. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472494
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  • 7
    Electronic Resource
    Electronic Resource
    Ab initio molecular-orbital study of the trichlorine radical, Cl3 (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 2771-2783 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a rigorous ab initio study of the ground and low-lying excited-state potential-energy surfaces (PESs) of the Cl3 radical at CASSCF, CASPT2, and MRSDCI levels of theory. The ground state has two Cl(centered ellipsis)Cl2 van der Waals complexes, X˜L and X˜′B. The linear asymmetric minimum (X˜L) is 2Π, with a Cl–Cl distance r=3.90 bohr, and a Cl–M (M: the Cl2 center-of-mass) distance R=8.70 bohr. The bent asymmetric minimum (X˜′B) is of 2A′ symmetry, with r=3.90 bohr, R=6.85 bohr, and the angle between r(circumflex) and R(circumflex), γ=68.4°. Spin–orbit CI (configuration interaction) predicts that the global minimum is linear X˜L (2Π3/2) with a bond dissociation energy of De(Cl2(X)-Cl) of 280 cm−1. Low-lying doublet excited states have only one strongly bound structure, a linear symmetric A˜L (1 2Πg) state with a bond distance of 4.67 bohr. This state is bound by ∼4300 cm−1 with respect to the Cl2(3Πu)+Cl asymptote, and its minimum lies about 8700 cm−1 above the X˜L van der Waals minimum. Transition dipole moment calculations show that the A˜–X˜ transition is fully allowed. Two bound quartet minima were located. The most deeply bound was QD3h (1 4A1′) with a D3h equilibrium geometry (r=5.00 bohr) about 11 300 cm−1 above X˜L. The other state, QC2v (1 4A2) had a C2v equilibrium geometry (r1=4.83 bohr and θ=101.7°) and an energy of about 13 500 cm−1 relative to X˜L. Although Cl3(X˜) is shown to be unstable, the present results support the notion that Cl3 participates in Cl atom recombination processes. However, the energies and transition moments of the low-lying excited states are not consistent with electronic spectra that have been tentatively assigned to Cl3. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475668
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  • 8
    Electronic Resource
    Electronic Resource
    Ab initio calculations on the diacetylene dimer: HCCCC(H)C(H)CCCHPresented at the 9th ICQC Conference in Atlanta, GA, 1997. (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 66 (1998), S. 189-202 
    Details
    ISSN: 0020-7608
    Keywords: diacetylene ; dimer ; C8H4 ; ab initio ; DFT ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Geometry optimizations were performed for singlet, triplet, and quintet states on the planar structures (in C2h and C2v symmetries) of the diacetylene dimer, using restricted open-shell Hartree-Fock (ROHF), unrestricted Hartree-Fock (UHF), and unrestricted hybrid density functional theory (UB3LYP) methods, with 6-31G(d) and 6-311G(d, p) basis sets. The 1Ag state of the planar van der Waals dimer is lower in energy than are any covalently bonded dimers. At our best B3LYP/6-311G(d, p) level, the most stable covalently bonded diacetylene dimer is the 3Bu state in C2h symmetry, 11 kcal mol-1 above the van der Waals dimer, followed by the 3B2 state in C2v symmetry with 13 kcal mol-1 above the van der Waals dimer. Both structures were confirmed to be local minima. The two diacetylene monomers of these structures are bridged through a single bond and they exhibit a small bend at the neighboring carbons to the bridge, trans to the hydrogens. The 1Bu and 5Ag states in C2h and the 1B2 and 5A1 states in C2v are between 39 and 43 kcal mol-1 above the van der Waals dimer.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 189-202, 1998
    Additional Material: 13 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Theoretical study of reactions of N2O with NO and OH radicals (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 28 (1996), S. 693-703 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of N2O with NO and OH radicals have been studied using ab initio molecular orbital theory. The energetics and molecular parameters, calculated by the modified Gaussian-2 method (G2M), have been used to compute the reaction rate constants on the basis of the TST and RRKM theories. The reaction N2O + NO → N2 + NO2 (1) was found to proceed by direct oxygen abstraction and to have a barrier of 47 kcal/mol. The theoretical rate constant, k1 = 8.74 × 10-19 × T2.23 exp (-23,292/T) cm3 molecule-1 s-1, is in close agreement with earlier estimates. The reaction of N2O with OH at low temperatures and atmospheric pressure is slow and dominated by association, resulting in the HONNO intermediate. The calculated rate constant for 300 K ≤ T ≤ 500 K is lower by a few orders than the upper limits previously reported in the literature. At temperatures higher than 1000 K, the N2O + OH reaction is dominated by the N2 + O2H channel, while the HNO + NO channel is slower by 2-3 orders of magnitude. The calculated rate constants at the temperature range of 1000-5000 K for N2O + OH → N2 + O2H (2A) and N2O + OH → HNO + NO (2B) are fitted by the following expressions: $$k_{2A}=2.15\times 10^{-26}\times T^{4.72}\exp(-18,400/T),$$ $$k_{2B}=1.96\times 10^{-28}\times T^{4.33}\exp(-12,623/T),$$ in units of cm3 molecule -1s-1. Both N2O + NO and N2O + OH reactions are confirmed to enhance, albeit inefficiently, the N2O decomposition by reducing its activation energy. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.8
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  • 10
    Electronic Resource
    Electronic Resource
    Ab initio MO and TST calculations for the rate constant of the HNO+NO2→HONO+NO reaction (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 729-736 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potential-energy surfaces for various channels of the HNO+NO2 reaction have been studied at the G2M(RCC,MP2) level. The calculations show that direct hydrogen abstraction leading to the NO+cis-HONO products should be the most significant reaction mechanism. Based on TST calculations of the rate constant, this channel is predicted to have an activation energy of 6-7 kcal/mol and an A factor of ca. 10-11 cm3 molecule-1 s-1 at ambient temperature. Direct H-abstraction giving NO+trans-HONO has a high barrier on PES and the formation of trans-HONO would rather occur by the addition/1,3-H shift mechanism via the HN(O)NO2 intermediate or by the secondary isomerization of cis-HONO. The formation of NO+HNO2 can take place by direct hydrogen transfer with the barrier of ca. 3 kcal/mol higher than that for the NO+cis-HONO channel. The formation of HNO2 by oxygen abstraction is predicted to be the least significant reaction channel. The rate constant calculated in the temperature range 300-5000 K for the lowest energy path producing NO+cis-HONO gave rise to\documentclass{article}\pagestyle{empty}\begin{document}$ k_{a}=7.34\cdot 10^{-20}\ \rm{T}^{2.64}\ \rm{exp}(-2034/T)\ \rm{cm}^{3}\ \rm{molecule}^{-1}\ \rm{s}^{-1}. $\end{document}© 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 729-736, 1998
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