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Using the strong electron hole cage C20F19 acceptor, the NH2...M/M3O (M = Li, Na, and K) complicated donors with excess electron, and the unusual σ chain (CH2)4 bridge, we construct a new kind of electride molecular salt e–@C20F19–(CH2)4–NH2...M+/M3O+ (M = Li, Na, and K) with excess electron anion inside the hole cage (to be encapsulated excess electron–hole pair) serving as a new A–B–D strategy for enhancing nonlinear optical (NLO) response. An interesting push–pull mechanism of excess electron generation and its long-range transfer is exhibited. The excess electron is pushed out from the (super)alkali atom M/M3O by the lone pair of NH2 in the donor and further pulled inside the hole cage C20F19 acceptor through the efficient long σ chain (CH2)4 bridge. Owing to the long-range electron transfer, the new designed electride molecular salts with the excess electron–hole pair exhibit large NLO response. For the e–@C20F19–(CH2)4–NH2...Na+, its large first hyperpolarizability (β0) reaches up to 9.5 × 106 au, w...

Alkane C-H bond activation by various catalysts and enzymes has attracted considerable attention recently, but many issues are still unanswered. The conversion of ethane to ethanol and ethene by bare [Fe(III)═O](+) has been explored using density functional theory and coupled-cluster method comprehensively. Two possible reaction mechanisms are available for the entire reaction, the direct H-abstraction mechanism and the concerted mechanism. First, in the direct H-abstraction mechanism, a direct H-abstraction is encountered in the initial step, going through a collinear transition state C···H···O-Fe and then leading to the generation of an intermediate Fe-OH bound to the alkyl radical weakly. The final product of the direct H-abstraction mechanism is ethanol, which is produced by the hydroxyl group back transfer to the carbon radical. Second, in the concerted reaction mechanism, the H-abstraction process is characterized via overcoming four/five-centered transition states (6/4)TSH_c5 or (4)TSH_c4. The second step of the concerted mechanism can lead to either product ethanol or ethene. Moreover, the major product ethene can be obtained through two different pathways, the one-step pathway and the stepwise pathway. It is the first report that the former pathway starting from (6/4)IM_c to the product can be better described as a proton-coupled electron transfer (PCET). It plays an important role in the product ethene generation according to the CCSD(T) results. The spin-orbital coupling (SOC) calculations demonstrate that the title reaction should proceed via a two-state reactivity (TSR) pattern and that the spin-forbidden transition could slightly lower the rate-determining energy barrier height. This thorough theoretical study, especially the explicit electronic structure analysis, may provide important clues for understanding and studying the C-H bond activation promoted by iron-based artificial catalysts.

To realize the chemistry of a multicage organic molecule with excess electron, as a model, by confining an excess electron inside a double-cage single molecule, the structures of e⁻@C₂₄F₂₂(NH)₂C₂₀F₁₈ (e⁻@AB) and e⁻@C₂₀F₁₈(NH)₂C₂₀F₁₈ (e⁻@BB') are obtained at the B3LYP/6-31G(d) + 4s4p theory level. It is confirmed that the excess electron is mainly confined inside one cage with larger interior electronic attractive potential (A for e⁻@AB and B for e⁻@BB') in the ground state, while the electron is localized in the other one in the first excited state. Owing to such excess electron localizations, an interesting intercage excess electron transfer transition takes places. This intercage excess electron transfer transition exhibits five characteristics: (1) the excess electron transfer from one cage to another (A → B for e⁻@AB and B → B' for e⁻@BB′'); (2) the transition is between the ground and first excited state; (3) the wavelength and strength are the largest; (4) the transition accompanies a significant charge transfer (Δq0.8) and molecular dipole moment change (Δμ20 D); (5) the transition corresponds to SOMO → LUMO. For the transition, the oscillator strength is larger and the wavelength is shorter for the asymmetric structure (e⁻@AB) than for the symmetric one (e⁻@BB'), which indicates that the intercage excess electron transfer transition may be regulated by changing the size of cage. This work is useful for the designs of organic electronic sponges (porous organic electrides), organic conductor with excess electrons, and photoelectric and nanoelectronic devices.

Electronic states of the CH(3)Se and its cation CH(3)Se(+) have been studied using the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with the ANO-RCC(TZP) basis set. To investigate the Jahn-Teller effect on the CH(3)Se radical, C(s) symmetry was used for CH(3)Se in calculations. The results show that the Jahn-Teller effect is very small (69 cm(-1)) and the 1(2)A' state is slightly more stable than the 1(2)A'' state (8 cm(-1)). The CH(3)Se has been found to have a 1(2)A' ground state with a C-Se bond distance of 1.975 A. The computed C-Se stretching nu(6)(a') frequency is 554.1 cm(-1), which is in good agreement with the experimental values of 600 +/- 60 cm(-1). The calculations for CH(3)Se at 3.621 and 5.307 eV are attributed to 1(2)A' --2(2)A'(1(2)A(1)) and 1(2)A' --2(2)A'', respectively. The vertical and adiabatic ionization energies were obtained to compare with the PES data.

The AlCCH radical is a photolysis product of the aluminum-acetylene adducts and has been considered as a molecule with potential interest in astrophysics. In this study, the low-lying electronic states of the AlCCH radical, cation, and anion have been studied by using complete active space self-consistent field and multiconfigurational second-order perturbation theory. The geometrical parameters, electron configurations, excitation energies, oscillator strengths, and harmonic vibrational frequencies are calculated in C(S) symmetry. For the X(1)Sigma(+) state of AlCCH, the calculated C-C and C-Al stretching modes are in good agreement with experimental reports. Moreover, the vertical excitation energy (T(v)) of 1(1)Pi is 3.68 eV, which is close to the experimental value of 3.57 eV. The electron transitions of AlCCH(+), X(2)Sigma(+) --> 1(2)Pi, X(2)Sigma(+) --> 2(2)Sigma(+), and X(2)Sigma(+) --> 1(2)Sigma(-), are predicted at 2.57, 4.51, and 4.61 eV, respectively. For AlCCH(-), the transition X(2)Pi --> 1(2)Sigma(-) occurs at 3.02 eV. The ionization potentials of AlCCH are computed in order to provide a theoretical guidance to the photoelectron spectrum of the AlCCH radical.

The complex triplet potential energy surface for the reaction of ground-state atomic carbon C(3P) with propylene C3H6 is explored at the B3LYP/6-311G(d,p), QCISD/6-311G(d,p), and G3B3 (single-point) levels. Various possible reaction pathways are probed. It is shown that the reaction is initiated by the addition of C(3P) to the C=C bond of C3H6 to generate barrierlessly the three-membered ring isomer 1 CH3-cCHCCH2, followed by the ring-opening process to form 2a trans-CH3CHCCH2, which can easily interconvert to 2b cis-CH3CHCCH2. Starting from 2 (2a, 2b), the most feasible pathway is the internal C-H bond rupture of 2a leading to P4(2CH3CCCH2 + 2H), terminal C-H bond cleavage of 2 (2a,2b) to form P5(2CH3CHCCH + 2H), or direct C-C bond fission of 2b to form P7(2CH2CCH + 2CH3), all of which may have comparable contributions to the title reaction. Much less competitively, 2a takes a 1,2-H-shift to form 5a trans-cis-CH3CHCHCH, followed by a C-C bond rupture leading to P6(1C2H2 + 3CH3CH). Because the intermediates and transition states involved in the feasible pathways all lie below the reactant, the title reaction is expected to be rapid, which is consistent with the measured large rate constant. The present article may provide some useful information for future experimental investigation of the title reaction.

A new class of metal-nonmetal-metal sandwich structures M3-CO3-M3' (M, M' = Li, Na, K) with all real frequencies is obtained at the second-order Möller-Plesset theory (MP2) method with the 6-311+G (2d) basis set. Because the sandwich molecule M3-CO3-M3' is composed of superatoms (M3, CO3, and M3'), it is a sandwich "superomolecule". The superatoms M3 and M3' are electron donors and CO3 is the acceptor, and then there is a strong charge transfer between M3 (or M3') and CO3 superatom, so M3-CO3-M3' can be denoted as M3(+)CO3(2-)M3'(+). Owing to the CO3(2-) anion in the middle repulsing the valence electrons of two metal rings (M3 and M3') forming a pair of excess electrons, the compound with excess electrons is also a novel electride. In metal-nonmetal-metal sandwich compound M3(+)CO3(2-)M3'(+), superatom units M3(+) and M3'(+) exhibit unusual sigma-aromaticity: the maximum negative nucleus-independent chemical shift (NICSmax) value of each aromatic ring (M3(+) and M3'(+)) does not locate at the center of the ring plane but locates outside the ring plane. The distance value from the center of the M3(+) or M3'(+) ring plane to the point with NICSmax ranges from 0.8 to 1.9 A. This shows a notable out-of-plane sigma-aromaticity for these sandwich compounds. What is the reason? We find that the out-of-plane sigma-aromaticity of M3(+) (or M3'(+)) results from the action of CO3(2-)M3'(+) (or M3(+)CO3(2-)). For electric property, on account of excess electrons, the sandwich electride M3-CO3-M3' without the central symmetry can exhibit large static first hyperpolarizability (beta0). For Na3-CO3-K3, the beta0 value is close to 56,000 au.

A direct ab initio dynamics method was used to study the mechanism and kinetics of the reaction CF(3)CHFOCH(3) + OH. Two reaction channels, R1 and R2, were found, corresponding to H-abstraction from a CH(3) group and a CHF group, respectively. The potential energy surface (PES) information was obtained at the G3(MP2)//MP2/6-311G(d,p) level. The standard enthalpies of formation for the reactant (CF(3)CHFOCH(3)) and products (CF(3)CHFOCH(2) and CF(3)CFOCH(3)) were evaluated via isodesmic reactions at the same level. Furthermore, the rate constants of two channels were calculated using the canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions over a wide temperature range of 200-3000 K. The dynamic calculations demonstrate that reaction R1 dominates the overall reaction when the temperature is lower than 800 K whereas reaction R2 becomes more competitive in the higher temperature range. The calculated rate constants and branching ratios are both in good agreement with the available experimental values.

The complex doublet potential energy surface for the ion-molecule reaction of HCN(+) with C(2)H(4) is investigated at the B3LYP/6-311G(d,p) and CCSD(T)/6-311++G(3df,2pd) (single-point) levels. The initial association between HCN(+) and C(2)H(4) forms three energy-rich addition intermediates, 1 (HCNCH(2)CH(2)(+)), 2 (HC-cNCH(2)CH(2)(+)), and 3 (N-cCHCH(2)CH(2)(+)), which are predicted to undergo subsequent isomerization and decomposition steps. A total of nine kinds of dissociation products, including P(1) (HCN + C(2)H(4)(+)), P(2) (HCNCHCH(2)(+) + H), P(3) (NCCH(2) + CH(3)(+)), P(4) (CN + C(2)H(5)(+)), P(5) (NCCHCH(2)(+) + H(2)), P(6) (HNCCHCH(2)(+) + H), P(7) (c-CHCCH(2)N(+) + H(2)), P(8) (c-NHCCH(2)C(+) + H(2)), and P(9) (HNCCCH(+) + H(2) + H), are obtained. Among the nine products, P(1) is the most abundant product. P(2) is the second feasible product but is much less competitive than P(1). P(3), P(4), P(5), and P(6) may have the lowest yields observed. Other products, P(7), P(8), and P(9), may become feasible at high temperature. Because the intermediates and transition states involved in the most favorable pathway all lie below the reactant, the HCN(+) + C(2)H(4) reaction is expected to be rapid, which is confirmed by experiment. The present calculation results may provide a useful guide for understanding the mechanism of HCN(+) toward other unsaturated hydrocarbons.

Geometries of 10, 7, and 6 low-lying states of the HCCN neutral radical, its anion and cation, were optimized by using the complete active space self-consistent field (CASSCF) method in conjunction with the aug-cc-pVTZ basis set, respectively. Taking the further correlation effects into account, the second-order perturbations (CASPT2) were carried out for the energetic correction. Vertical excitation energies (T(v)) at the ground state geometry of the HCCN neutral radical were calculated for 11 states. The results of our calculations suggest that the spin-allowed transitions of HCCN at 4.179, 4.395, 4.579, 4.727 and 5.506 eV can be attributed to X(3)A'' --> 2(3)A'', X(3)A'' --> (3)A', X(3)A --> 3(3)A'', X(3)A'' --> 2(3)A', and X(3)A'' --> 3(3)A', respectively. The singlet-triplet splitting gap of HCCN is calculated to be 0.738 eV. The vertical and adiabatic ionization energies were obtained to compare with the PES data. The results we obtained were consistent with the available experiment results.

The photophysics of a series of molecular organic light-emitting diodes (OLEDs) has been studied by theoretical calculation. These molecular OLEDs have been integrated by an electron- and hole-transporting components as well as an emitting components into the donor-pi-acceptor (D-pi-A) structures: 2-carbazolyl-7-dimesitylboryl-9,9-diethylfluorene (1), trans-4'-N-carbazolyl-4-dimesitylborylstilbene (2), and trans-2-[(4'-N-carbazolyl)styryl]-5-dimesitylborylthiophene (3). To reveal the relationship between the structures and properties of these multifunctional electroluminescent materials, the ground- and excited-state geometries were optimized at the B3LYP/6-31G(d), HF/6-31G(d), and CIS/6-31G(d) levels, respectively. The ionization potentials and electron affinities were computed. The mobilities of hole and electron in these compounds were studied computationally based on the Marcus electron transfer theory. The lowest excitation energies (E(g)) and the maximum absorption and emission wavelengths of these compounds were calculated by time-dependent density functional theory methods. The solvent effect on the emission spectra of these compounds was considered by a polarizable continuum model. As a result of these calculations, it was concluded that the electron injections of these compounds are much easier than Mes(2)B[p-4,4'-biphenyl-NPh(1-naphthyl)], and the diethylfluorene-based compound has higher electron mobility and better equilibrium properties as compared to the stilbene-based and styrylthiophene-based compounds.

The hydrogen abstraction reactions by a hydroxyl radical from 1,1,2,2,3-fluorinated propane (CF 2 HCF 2 CFH 2 ) have been investigated by the dual-level direct dynamics method. Three equilibrium conformers (I, II, III) of CF 2 HCF 2 CFH 2 , one with C s and two with C 1 symmetries, are identified by the rotations of -CFH 2 and -CF 2 H groups. Two transition states are located for the conformer I (C s symmetry) + OH → products (Rl) reaction, and three distinct transition states are identified for conformers II and III (C 1 symmetry) + OH → products (R2 and R3). The optimized geometries and harmonic vibrational frequencies of all reactants, complexes, transition states, and products are calculated at the BB1K/6-31+G(d,p) level of theory. The single-point energy calculations are performed at the G3(MP2) level using the BB1K geometries. Using improved canonical variational transition-state theory (ICVT) with the small-curvature tunneling correction (SCT), the rate constants for each channel are calculated over a wide temperature range of 200-2000 K. It is found that the H-abstraction reaction from the -CFH 2 group is the predominant product channel for three reactions. The total rate constant is evaluated by the Boltzmann distribution function, and the agreement between theoretical and experimental values is good.

The electronic structures and stabilities of pure M(12)- and M(12)(2-) were systematically investigated within density functional theory. The nucleus-independent chemical shifts (NICSs) of I(h) Sn(12)(2-) and Pb(12)(2-) are -5.0 and -20.7 ppm, respectively, based on B3LYP/aug-cc-pVDZ-PP predictions, whereas the NICS of Sn(12)(2-) is predicted to be 1.1 ppm by B3LYP/LanL2DZ. A startling conclusion is that the NICS4d of Sn(12)(2-) and NICS(5d) of Pb(12)(2-) are -5.0 and -7.5 ppm, respectively, suggesting the significant contribution of the inner d orbitals to the total NICS values. This provides the first quantitative evidence for the existence of "d-orbital aromaticity" in Sn- and Pb-based clusters with three-dimensional structures. The d orbitals also contribute to the total NICSs of the K-coordinated clusters. The NICS predictions suggest that larger basis sets including d-orbitals are needed to analyze the aromaticity of some main-group-metal-based clusters (e.g., Sn- and Pb-based clusters) to obtain accurate predictions.

The structures, binding energies, and electronic properties for Al7X, Al7X-, Al13X-, Al13X2-, and Al13X12- (X = F, Cl, Br) were studied at the B3LYP/6-311+G(2d,p) level. Among the systems studied, Al7 and Al13 clusters in Al7X and Al13X- reveal alkali-like and halogen-like superatom characters, respectively. Al7 can bind with one halogen atom to form a salt-like compound as Al7+delta-X-delta. Al13- can combine with one halogen atom to form a diatomic halogen anion Al13X-. However, when adding more halogens, the superatom structure would be destroyed, resulting in low-symmetry compounds with the center Al atom moving toward the cluster surface. The structures of Al13X1,2,12- (X = F, Cl, Br) are similar to those of X = I; however, their binding energies and electron structures are much different. In addition, the analyses of the calculated NBO charges show that Cl and Br have similar properties, but much different from F, when interacting with the Al clusters. The Al-Cl and Al-Br bonds have more covalent character in Al7X and Al13X2,12-, in contrast to the corresponding Al-F bond, which has prominent ionic character.

Using the complete active space self-consistent field (CASSCF) method with large atomic natural orbital (ANO-L) basis set, four electronic states of the HSO neutral radical are optimized. The vertical transitions of the HSO neutral radical are investigated by using the same method under the basis set of ANO-L functions augmented with a series of adapted 1s1p1d Rydberg functions, through which eight valence states and eight Rydberg states are probed. Ionic states of the HSO neutral radical are extensively studied in both cases of the adiabatic and vertical ionization, from which the relatively complete understanding of ionization energies is given. To include further correlation effects, the second-order perturbation method (CASPT2) is implemented, and the comparison between CASSCF and CASPT2 methods is performed.

Complete active space (CAS) calculations with 6-311++g(3df,3pd) basis sets were performed for a large number of electronic states of the nitrate free radical (CH3N/CH3CH2N) and their positive and negative ions. All calculated states are valence states, and their characters are discussed in detail. To investigate the Jahn-Teller effect on the CH3N radical, Cs symmetry was used for both CH3N and CH3CH2N in calculations. The results (CASPT2 adiabatic excitation energies and CASSI oscillator strengths) suggest that the calculated transitions of CH3N at 32172 and 32139 cm(-1) are attributed to the 2(3)A' ' --1(3)A' ' and 1(3)A' --1(3)A' ', respectively, which is in accordance with the A3E --X3A2 emission spectrum at T0 = 31 817 cm(-1). The calculated transitions of CH3CH2N at 334 nm are attributed to the 1(3)A' ' --2(3)A' ' and 1(3)A' ' --1(3)A', respectively, which is in accordance with the UV absorption spectrum of a series of 11 bands beginning at 335 nm. The vertical and adiabatic ionization energies were obtained to compare with the PES data. These results are in agreement with previous experimental data, which is discussed in detail.

By counterpoise-corrected optimization method, the six antiaromatic ring pi multi-hydrogen bond structures with diversiform shapes for (H2O)n-C4H4 (n = 1,2) have been obtained at the MP2/aug-cc-pVDZ level. At the CCSD(T)/aug-cc-pVDZ level, the interaction energy obtained mainly depends on the numbers of H2O and fold numbers of the pi multi-hydrogen bond. The interaction energy order is -2.342 (1a with pi mono-hydrogen)-2.777 (1b with pi bi-hydrogen)-4.683 (2a with pi bi-hydrogen)-4.734 (2b with pi tri-hydrogen)-4.782 (2c with pi tri-hydrogen)-5.009 kcal/mol (2d with pi tetra-hydrogen bond). Strangely, why is the interaction energy of the pi bi-hydrogen bond in 1b close to that of the pi mono-hydrogen bond in 1a (their difference is only 15.7%)? The reason is that a pi-type H-bond (as an accompanying interaction) between two lone pairs of the O-atom and a near pair of H-atoms of C4H4 exists shoulder by shoulder in structures 1a, 2a, 2b, and 2c and contributes to the interaction energy. Another accompanying interaction, a repulsive interaction between the pi H-bond (using the H-atom(s) of H2O) and the near pair of H-atoms of C4H4, is also found. For the structures and interaction energies, the pi-type H-bond produces four effects: bending the strong pi H-bond, attracting the pair of H-atoms of C4H4 so that they deviate from the C4 ring plane, showing the interaction energy contribution, and bringing the larger electron correlation contribution. The repulsive interaction also produces four effects: pushing the pair of H-atoms of C4H4 so that they deviate from its ring plane, elongating the distance of the pi H-bond, promoting the formation of pi-type H-bond, and slightly influencing the interaction energy. In the present paper, one C=C bond with two H2O (over and below the ring plane) forms a pi H-bond link in two ways: a strong-weak pi H-bond link and a strong-strong pi H-bond link. The stability contribution of the former is more favorable than the latter. One H2O forms a pi H-bond with C4H4 in two ways. One strong pi H-bond part (over or below the ring plane) always is accompanied by another H-bond part. The accompanying part is either a weak pi H-bond or pi-type H-bond.

The stable structures, energies, and electronic properties of neutral, cationic, and anionic clusters of Al(n) (n = 2-10) are studied systematically at the B3LYP/6-311G(2d) level. We find that our optimized structures of Al5(+), Al9(+), Al9(-), Al10, Al10(+), and Al10(-) clusters are more stable than the corresponding ones proposed in previous literature reports. For the studied neutral aluminum clusters, our results show that the stability has an odd/even alternation phenomenon. We also find that the Al3, Al7, Al7(+), and Al7(-) structures are more stable than their neighbors according to their binding energies. For Al7(+) with a special stability, the nucleus-independent chemical shifts and resonance energies are calculated to evaluate its aromaticity. In addition, we present results on hardness, ionization potential, and electron detachment energy. On the basis of the stable structures of the neutral Al(n) (n = 2-10) clusters, the Al(n)O (n = 2-10) clusters are further investigated at the B3LYP/6-311G(2d), and the lowest-energy structures are searched. The structures show that oxygen tends to either be absorbed at the surface of the aluminum clusters or be inserted between Al atoms to form an Al(n-1)OAl motif, of which the Al(n-1) part retains the stable structure of pure aluminum clusters.

A detailed computational study is performed on the unknown radical-molecule reactions between HCO/HOC and acetylene (C2H2) at the CCSD(T)/6-311G(2d,p)//B3LYP/6-311G(d,p)+ZPVE, Gaussian-3//B3LYP/6-31G(d), and Gaussian-3//MP2(full)/6-31G(d) levels. For the HCO + C2H2 reaction, the most favorable pathway is direct C-addition forming the intermediate HC=CHCH=O followed by a 1,3-H-shift leading to H2C=CHC=O, which finally dissociates to the product C2H3 + CO. The overall reaction barrier is 13.8, 10.5, and 11.3 kcal/mol, respectively, at the three levels. The quasi-direct H-donation process to produce C2H3 + CO with barriers of 14.0, 14.1, and 14.1 kcal/mol is less competitive. Thus only at higher temperatures could the HCO + C2H2 reaction play a role. In contrast, the HOC + C2H2 reaction can barrierlessly generate C2H3 + CO via the quasi-direct H-donation mechanism proceeding via a prereactive complex with OH...C2 hydrogen bonding. This is suggestive of the potential importance of the HOC + C2H2 reaction in both combustion and interstellar processes. However, the direct C-addition channel is much less competitive. For both reactions, the possible formation of the intriguing interstellar molecules propadiene and propynal is also discussed. The present theoretical study represents the first attempt to probe the reaction mechanism between HOC and pi-systems. Future laboratory investigations on both reactions (particularly HOC + C2H2) are recommended.

The complex singlet potential energy surface for the reaction of CN with NO2, including 9 minimum isomers and 10 transition states, is explored computationally using a coupled cluster method and a density functional method. The most favorable association of CN with NO2 was found to be a barrierless carbon-to-nitrogen approach process forming an energy-rich adduct a (NCNO2) followed by C-N bond rupture along with C-O bond formation to give b1 (trans-NCONO), which can easily convert to b2 (cis-NCONO). Our results show that the product P1 (NCO + NO) is the major product, while the product P2 (CNO + NO) is a minor product. The other products may be of significance only at high temperatures. Product P1 (NCO + NO) can be obtained through path 1 P1: R --> a --> b1 (b2) --> P1 (NCO + NO), whereas the product P2 (CNO + NO) can be formed through path P2: R --> a --> b1 --> b2 --> c1 (c2) --> P2 (CNO + NO). Because the intermediates and transition states involved in the above two channels are all lower than the reactants in energy, the CN + NO2 reaction is expected to be rapid, as is confirmed by experiment. Therefore, it may be suggested as an efficient NO2-reduction strategy. These calculations indicate that the title reaction proceeds mostly through singlet pathways and less go through triplet pathways. The present results can lead us to understand deeply the mechanism of the title reaction and can be helpful for understanding NO2-combustion chemistry.

The multichannel reactions (1) HOCl + F --products and (2) HOBr + F --products have been investigated using the dual-level direct dynamics method. The minimum energy paths (MEPs) are calculated at both the MPW1K/6-311G(d,p) and QCISD/6-311G(d,p) levels, then the single-point energies are further corrected at the QCISD(T)/6-311++G(3df,3pd) level of theory. There are hydrogen-bonded complexes with the energies less than those of the reactants or products located at the entrance or exit channel of both hydrogen abstraction reactions; while for the halogen abstraction channels only one complex exists at the reactant side in the bromine abstraction channel. The rate constants are evaluated by the improved canonical variational transition-state theory (ICVT). The agreement of the rate constants with available experimental values for two reactions at room temperature is good. Theoretical results indicate that for the reaction HOCl + F, hydrogen abstraction channel leading to the formation of HF + ClO will predominate the reaction over the whole temperature range, and the reaction of HOBr + F may proceed mainly through the bromine abstraction channel at the lower temperature while the contribution of hydrogen abstraction channel will become significant as the temperature increases. Because of lack of the kinetic data of these reactions, the present theoretical results are expected to be useful and reasonable to estimate the dynamical properties of these reactions over a wide temperature range where no experimental value is available.

A detailed computational study is performed on the radical-molecule reaction between the vinyl radical (C2H3) and formaldehyde (H2CO), for which only the direct hydrogen abstraction channel has been considered by previous and very recent theoretical studies. At the Gaussian-3//B3LYP/6-31G(d) and CBS-QB3 levels, the direct H-abstraction forming C2H4 + HCO has barriers of 3.9 and 4.7 kcal/mol, respectively. The addition barrier to form H2CCHCH2O has barriers of 2.8 and 2.3 kcal/mol, respectively. Subsequently, there are two highly competitive dissociation pathways for H2CCHCH2O: One is the formation of the direct H-extrusion product H2CCHCHO + H, and the other is the formation of C2H4 + HCO via the intermediate H2CCH2CHO. Surely, the released energy is large enough to drive the secondary dissociation of HCO to H + CO. Because the involved transition states and intermediates of the H2CCHCH2O evolution all lie energetically lower than the entrance addition transition state, the addition-elimination is more competitive than the direct H-transfer for the C2H3 + H2CO reaction, in contrast to previous expectation. The present results can be useful for future experimental investigation on the title reaction.

The complex doublet potential-energy surface for the reaction of CCO with NO2, including 8 minimum isomers and 17 transition states, is explored theoretically using the coupled cluster and density functional theory. The association of CCO with NO2 was found to be a barrierless process forming an energy-rich adduct a (OCCNO2) followed by oxygen shift to give b (O2CCNO). Our results show that the product P1 (CO2 + CNO) is the major product with absolute yield, while the product P4 (2CO + NO) is the minor product with less abundance. The other products may be undetectable. The product P1 (CO2 + CNO) can be obtained through R --a --b --P1 (CO2 + CNO), whereas the product P4 (2CO + NO) can be obtained through two channels R --a--b --c --(d, g) --P2 (OCNO + CO) --P4 (2CO + NO) and R --a --b --f --P3 (c-OCC-O + NO) --P4 (2CO + NO). Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the CCO + NO2 reaction is expected to be rapid, which is consistent with the experimental measurement in quality. The present study may be helpful for further experimental investigation of the title reaction.

The structures, energetics, spectroscopies, and isomerization of various doublet Si2CP species are explored theoretically. In contrast to the previously studied SiC2N and SiC2P radicals that have linear SiCCN and SiCCP ground states, the title Si2CP radical has a four-membered-ring form cSiSiPC 1 (0.0 kcal/mol) with Si-C cross-bonding as the ground-state isomer at the CCSD(T)/6-311G(2df)//B3LYP/6-311G(d)+ZPVE level, similar to the Si2CN radical. The second low-lying isomer 2 at 11.6 kcal/mol has a SiCSiP four-membered ring with C-P cross-bonding, yet it is kinetically quite unstable toward conversion to 1 with a barrier of 3.5 kcal/mol. In addition, three cyclic species with divalent carbene character, i.e., cSiSiCP 7, 7' with C-P cross-bonding and cSiCSiP 8 with Si-Si cross-bonding, are found to possess considerable kinetic stability, although they are energetically high lying at 44.4, 46.5, and 41.4 kcal/mol, respectively. Moreover, a linear isomer SiCSiP 5 at 44.3 kcal/mol also has considerable kinetic stability and predominantly features the interesting cumulenic /Si=C=Si=P/* form with a slight contribution from the silicon-phosphorus triply bonded form /Si=C*-Si[triple bond]P/. The silicon-carbon triply bonded form *Si[triple bond]C-Si[triple bond]P/ has negligible contribution. All five isomers are expected to be observable in low-temperature environments. Their bonding nature and possible formation strategies are discussed. For relevant species, the QCISD/6-311G(d) and CCSD(T)/6-311+G(2df) (single-point) calculations are performed to provide more reliable results. The calculated results are compared to those of the analogous C3N, C3P, SiC2N, and Si2CN radicals with 17 valence electrons. Implications in interstellar space and P-doped SiC vaporization processes are also discussed.

In contrast to the abundant data on the neutral-neutral reactions, little is known about the ion-molecule reactions involving silicon ions. A detailed mechanistic study at the B3LYP/6-311G(d,p) and CCSD(T)/6-311+G(2df,p) (single-point) computational levels was reported for the reactions of SiCN + /SiNC + with a series of σ-bonded molecules HX (X = H, CH 3 , F, NH 2 ). Together with the recently studied SiCN + /SiNC + + H 2 O reactions, all of these reactions have nucleophilic substitution as their major pathway. Insertion is a much slower reaction. By contrast, the known atomic Si + and C 2 N + ion-molecule reactions go by insertion. Generally, the initial gas-phase condensation between SiCN + /SiNC + and HX (except the nonionic H 2 ) effectively forms the adduct HX...SiCN + /HX...SiNC + . The stability of the adduct increases with the electron-donating ability of X. Even at low temperatures, reactions with the electron donors NH 3 , H 2 O, and HF proceed rapidly to generate the fragments SiX + + HCN (dominant) and SiX + + HNC (minor). This suggests that such reactions may be useful in the synthesis of novel Si-X bonded species. However, the reactions of SiCN + with completely saturated CH 4 and H 2 produce fragments only at high temperatures, and SiNC + may even be unreactive. The calculated results may be helpful for understanding the chemistry of SiCN-based microelectric and photoelectric processes in addition to astrophysical processes in which the [Si,C,N] + ion is involved. The results can also provide useful mechanistic information for the analogous ion-molecule reactions of the monovalent silicon-bearing ions.

"Inverse sodium hydride" (AdzH(+)Na-) is an alkalide compound synthesized in recent experiments containing the unusual charge distribution H+ and Na- (inverse charge state). The new class of compounds interests scientists to investigate their especial structures and properties. In this paper, the structures of three alkalides compounds, (Me)3NH(+)Na-, AdzH(+)Na-, and AdzLi(+)Na-, have been obtained in theory. Especially, the structure of AdzLi(+)Na- is still researched by experimental scientists. We investigated the NLO properties of the alkalides complexes for the first time and found that inverse sodium hydride AdzH(+)Na- has a considerably large NLO response beta0 = 5.7675 x 10(4) au by density functional theory (DFT). To understand the essential features of the large NLO properties, four related systems have been also calculated. Their first hyperpolarizabilities are beta0 = 7.357 x 10(3) au for (Me)3NH(+)Na-, beta0 = 3.9 au for (Me)3NH+, beta0 = 1.10 x 10(2) au for (Me)3NH(+)Cl-, and beta0 = 6.20681 x 10(5) au for AdzLi(+)Na-, respectively. By comparing, we found that, first, the Na- anion plays a crucial role in the considerably large first hyperpolarizability of inverse sodium hydride and, second, the first hyperpolarizability of inverse sodium hydride increases with the charge value of the sodium anion. The above results are useful for designing potential NLO materials.

Various levels of calculations are applied to obtain the structures, energies, dipole moments, vibrational spectra, rotational constants, and isomerization of SiC3P species. A total of 27 minima which are connected by 40 interconversion transition states on the potential energy surface are located at the DFT/B3LYP/6-311G(d) level. The global minimum is found to be a linear SiCCCP of the 2Π electronic state. Besides the three-membered-ring isomer CC-cCPSi (36.2 kcal/mol), the four-membered-ring isomers P-cCCCSi (31.2 kcal/mol) and P-cSiCCC (79.1 kcal/mol), the five-membered-ring isomer cCPCCSi (46.6 kcal/mol), and the cagelike isomer pPSiCCC (56.8 kcal/mol) also possess great kinetic stability (more than 10.0 kcal/mol). The bonding natures of the relevant species are analyzed. The calculated results may be helpful for understanding the P-doped SiC vaporization process. The structures, energies, and bonding properties of the relevant species are compared with those of the SiC2N, SiC2P, and SiC3N analogues.

The potential energy surface of SiC3N is investigated at various levels. A total of 33 isomers are located connected by 44 interconversion transition states. At the CCSD(T)/6-311G(2d)//B3LYP/6-311G(d) level, the lowest lying isomer is linear SiCCCN with a 2Π electronic state whose structure mainly resonates between •|SiC⋮CC⋮N| and |SiCC•C⋮N|. The chainlike low-energy structures SiCCNC (25.0 kcal/mol), SiNCCC (33.9 kcal/mol), CCSiCN (42.9 kcal/mol), and CCSiNC (45.7 kcal/mol) possess large kinetic stability also. Another two kinetically very stable three-membered-ring structures with 2A‘ electronic states are located, i.e., CN-cCCSi (33.2 kcal/mol) and CN-cSiCC (40.7 kcal/mol), with a kinetic stability of 40.3 and 128.4 kcal/mol, respectively. Except for CN-cSiCC, other isomers mentioned above contain conjugative or hyperconjugative multiple bonding. Among the SiCnN series, SiC3N may be the first radical with stable cyclic isomers that can be detected in interstellar space. For the relevant structures, the...

The reaction of 3 C 2 radical with NO molecule is studied at the B3LYP/6-311G(d) level of theory. Both doublet and quartet potential energy surfaces (PES) are considered. On the doublet potential energy surface, we obtainfour major pathways in which the pathways 3 C 2 + NO ⇄ 1 CCNO → 2 (NC)CO → 3 CNCO → P 1 CN + CO and 3 C 2 + NO ⇄ 1 → 4 CC(NO) → 2 → 3 → P 1 CN + CO have lower energetics than the other two pathways that form the 3 O atom, namely 3 C 2 + NO ⇄ 1 CCNO → P 2 3 O + 2 CCN and 3 C 2 + NO ⇄ 1 CCNO → 5 ON(CC) → P 3 3 O + 2 CCN r i n g . However, the latter two pathways may compete with the former two pathways. The calculated energetics of the four pathways may account for the experimental results that CN is the primary product at low temperatures and 3 O is the main product at higher temperatures. The barrierless entrance to the first adduct isomer 1 and the tight transition states to the products P 1 , can provide a reasonable explanation for the experimentally observed negative temperature dependence of rate constants at low temperatures. The pathways on the quartet potential energy surface are less competitive than those on the doublet potential energy surface. Thus, they are negligible.

The structures, energetics, spectroscopies, and stabilities of the singlet and triplet Si 2 NP isomeric species are explored at the DFT/B3LYP, QCISD, and CCSD(T) (single-point) levels. A total of 23 minimum isomers and 32 interconversion transition states are located. Generally, the triplet species lie energetically higher than the singlet ones. At the CCSD(T)/6-31 I+G(2df)//QCISD/6-31 IG(d) level, there are two nearly isoenergetic singlet isomers as global minima, i.e., a linear SiNSiP 1 1 (0.0) and a puckered cSiNSiP 1 4 with P-N cross-bonding (-0.6). The third low-lying isomer is a planar four-membered ring cSiNSiP 1 5 (3.3) with Si-Si cross-bonding. All the three isomers have reasonable kinetic stabilities and might be observable either in laboratory or in space. Moreover, the structural and bonding analyses indicate that 1 1 possesses typical Si≡P triple bonding. Since up to now, stable Si=P triply bonded species are still experimentally unknown, isomer '1 may represent such a good example. Finally, the similarities and discrepancies of Si 2 NP are compared to the other analogous 18-valence electrons species AA'BB' (A, A' are group IV elements and B, B' are group V elements) such as C 2 N 2 and Si 2 P 2 . The present study is the first one to consider such series with three higher-row atoms.

The effects of intermolecular interaction on dipole moment (μ), the mean (α) and anisotropy (Δα) of the polarizability, and the first and second hyperpolarizabilities (β and γ, respectively) for four hydrogen bond dimers between two π-systems (HCN···HCN, HNC···HCN, HCN···HNC, and HNC···HNC) have been calculated in the finite-field approach. The properties were calculated at the MP4/d-aug-cc-pVTZ level. Intermolecular interaction significantly increases the first hyperpolarizabilities of four dimers between two π-systems (177% for HCN···HCN, 47.9% for HNC···HCN, 65.3% for HCN···HNC, and 37.9% for HNC···HNC). Intermolecular interaction effects of the second hyperpolarizabilities are 3.0% for HCN···HCN, −3.1% for HNC···HCN, 5.4% for HCN···HNC, and −2.1% for HNC···HNC. For the four dimers, electron correlation effects are important to the total and interaction electric properties.

The structures, energetics, spectroscopies, and isomerization of singlet and triplet SiC2S isomeric species are explored at various levels. At the B3LYP/6-311G(d) level, a total of 29 minimum isome...

The effects of the intermolecular interaction on dipole moment (μ), the mean (a) and anisotropy (Δα) of the polarizability, and the first and second hyperpolarizabilities (β and y, respectively) of HCN-HF and HNC-HF complexes have been calculated in finite-field approach. The augmented correlation-consistent basis sets x-aug-cc-pVXZ (x = s, d, t; X = D, T, Q) are employed to study the effects of the basis sets. Using the d-aug-cc-pVTZ basis set, we calculated the electric properties at the coupled-cluster theory with single and double substitutions and perturbatively linked triple excitations, CCSD(T) level. The electron correlation effects for those electric properties are discussed. The value of each electric property calculated for HCN-HF is less than that for HNC-HF. The μ = 2.2918 au, a = 23.186 au, Δα = 14.393 au, β = -6.03 au, and γ = 2553.4 au for HCN-HF; μ = 2.3338 au, a = 24.383 au, Δα = 14.875 au, β = 7.60 au, and y = 3049.3 au for HNC-HF. The electric properties coming from the interaction parts are as follows: μ i n t ) = 0.3908 au (17.1%), α i n t = 0.181 au (0.8%), Δα i n t = 4.300 au (29.9%), β i n t = 6.02 au (-99.8%), and γ i n t = -492.0 au (-19.3%) for HCN-HF; μ i n t = 0.4080 au (17.5%), α i n t = -0.084 au (0.3%), Δα i n t = 5.041 au (33.9%), β i n t = -7.20 au (-94.7%), and γ i n t = -931.7 au(-30.6%) for HNC-HF. The estimated electron correlation corrections are β c o r r = 6.59 au and γ c o r r = 549.2 au for HCN-HF and β c o r r = -9.49 au and γ c o r r = 1056.5 au for HNC-HF.

The ab initio direct dynamics approach is employed to study the hydrogen abstraction reaction of CH 3 CCl 3 + OH. The potential energy surface (PES) information is obtained at the MP2/6-311G(d,p) and G3(MP2) (single-point)levels of theory. A hydrogen-bonded complex is located in the reactant channel. Dynamics calculations are performed by variational transition-state theory with the interpolated single-point energy approach (VTST-ISPE). Canonical variational transition-state theory and a small curvature tunneling correction are included to calculate the rate constants within 200-2000 K. Both theoretical rate constants and activation energy are in good agreement with experimental ones over the measured temperature range, 222-761 K. The calculations show that the variational effect is small and the tunneling effect is significant in the lower temperature range.

The present calculations represent the first theoretical study of the mechanism of the reactions Cl + HOCl → products (R1) and H + HOCl → products (R2). A direct dynamics method is employed to perf...

The dynamical properties for the two hydrogen-abstraction reactions of 1,11-trichloroethane (CH 3 CCl 3 ) and 1,1,1-trifluoroethane (CH 3 CF 3 ) with chlorine atoms over the temperature range 200-1200 K are investigated theoretically. The minimum energy paths (MEPs) of both reactions are calculated at the BH&H-LYP/ 6-311+G(d,p) level, and the energies along the MEPs are further refined at the CCSD(T)/6-311+G(2df,2p) (single-point) level. For both reactions, the theoretical rate constants are in good agreement with available experimental results. Compared with the one previous theoretical investigation at the HF/6-31G(d) level followed by BAC-MP4 single-point energy calculations, our calculated rate constants are closer to the experimental values. The theoretical results show that for the title reactions the variational effect is small over the whole considered temperature range and the small-curvature tunneling effect is only important in the lower temperature range.

By means of ab initio direct dynamics method, the reactions H + CCl 4 → CCl 3 + HCl (1) and H + CHCl 3 → products (2) have been investigated theoretically to reveal their dynamical properties. The minimum energy paths (MEPs) of both reactions are calculated at the BH&H-LYP/6-311G(d,p) level, and the energies along the MEPs are further refined at the PMP4/6-311+G(3df,2p) (single-point) level. For reaction 2, both reaction channels, H-abstraction and Cl-abstraction, have been identified. Thus, the rate constants for each reaction channel as well as reaction 1 are calculated by the canonical variational transition state theory incorporating the small-curvature tunneling correction in the temperature range 200-5000 K. For reaction 1, the theoretical rate constants are in good agreement with the experimental values over the measured temperature range. For reaction 2, the total rate constants, which are calculated from the sum of the individual rate constants, are in excellent agreement with the experimental ones, and the temperature dependence of the branching ratios indicate that, at low-temperature range (T < 667 K), H-abstraction is the major reaction channels, whereas Cl-abstraction channels will significantly contribute to the whole reaction rate as the temperature increases.

Calculations at the QCISD(T)/6-311+G(d,p)//B3LYP/6-31G(d) level indicate that the participation of water can effectively lower the isomerization barrier from linear propargylium (H2CCCH+) to cyclop...

The potential energy surface of C2H2FO is investigated at CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p) level. The results show that isomers of 1, 3, 4, 5, 5‘, 8, 9, and 9‘ are stable, and the energy barriers are more than 30 kcal/mol. Isomer 2 has, relatively speaking, much lower kinetic stability. The three cyclic isomers 6, 6‘, and 7 are less stable than the former, but more stable than the latter. The other isomers, such as isomers 1‘, 3‘, 4‘, 10, and 11 are less stable than isomer 2 in kinetics. Only isomer 1 was synthesized experimentally, and the calculated frequencies are in good agreement with experimental values, so we conjecture that in the future, other stable isomers may be synthesized by the experimental methods, for example, coming from such reactions as FCCH + OH, CH2F + CO, and so forth. Compared to the analogous C2H3O radical isomers, the energy order is changed. This may be due to conjugation of the carbonyl group in isomer 1 CH2CFO with the substituent fluorine at the α-position.

The complex singlet potential energy surface of the CHClN 2 O system is investigated at the QCISD(T)/6-311G(d,p)//B3LYP/6-31G(d,p) level to explore the possible reaction mechanism of 1 CHCl radical with N 2 O. Thirty minimum isomers and 56 transition states are located. In various possible initial association ways, the end-N attack leading to HClCNNO a 1 is the most feasible pathway with the barrier of 8.9 kcal/mol. Starting from a 1 , the most feasible pathway is the direct cleavage of N-N bond leading to P 1 HClCN + NO or to undergo a concerted Cl-shift and N-N bond cleavage to form P 2 HCN + ClNO, both of which have a comparable contribution. In addition, a 1 can isomerizate to HClCNNO a 2 (a 3 ) followed by the rupture of N-N bond to form P 1 . Furthermore, the primary products P 1 and P 2 further dissociate to the same product P 1 6 HCN + NO + Cl. Much less competitively, a 3 can alternatively undergo a ring-closure process leading to HCl-c(CNNO) b followed by the dissociation to product P 3 N 2 + HClCO. The secondary dissociation of P 3 may form the final product P 1 0 N 2 + HCl + CO. The least favorable pathway should be that isomer a 2 undergoes a concerted H-migration and N-N bond rupture to form product P 4 ClCN + HNO. The similarities and discrepancies among the 1 CHX + N 2 O (X = H, F, and Cl) reactions are discussed in terms of the substitution effect and the electronegativity of halogen atom. The present paper may assist in future experimental identification of the product distributions for the title reaction and may be helpful for understanding the halocarbene chemistry.

The possible reaction mechanism of CH radical with CH3OH is investigated theoretically by a detailed potential energy surface calculation at the B3LYP/6-311G(d,p) and CCSD(T)/6-311+G(d,p) (single-p...

A detailed [C 2 H 2 NS + ] potential energy surface in singlet, including 45 minimum isomers and 57 transition states, is built up at the B3LYP/6-311G(d,p) and CCSD(T)/6-311G(2df,p) (single-point) levels in order to explore the mechanisms of the important ion-molecule reactions between CCN + /CNC + and H 2 S. For the reactions of both CCN + and CNC + toward H 2 S, product HCS + + HNC may be the most abundant followed by the much less HCNH + + CS and then HCS + + HCN. Significant discrepancies on the product distributions are found between our calculated results and previous experimental finding. On the other hand, the reaction of HCNH + + CS to form HCS + + HCN/HNC is also considered by the [C 2 H 2 NS + ] PES. For such reaction, the barrierless association may lead to the adduct HNC(H)CS + , while the proton-transfer may barrierlessly lead to product HCS + + HCN/HNC via the hydrogen-bound complexes SCH...NCH + /SCH...CNH + , The computations reported in this paper may represent the first theoretical study on the chemical reactivity of the C 2 N + ion and may thus provide a useful guide for understanding the mechanisms of the other analogous reactions such as those of C 2 N + with H 2 O, CH 4 , NH 3 . CH 3 OH, etc. The present calculations may also provide useful information for future laboratory investigations on the HCNH + + CS reactions that have not been previously studied. Interstellar implications of the title reactions are discussed.

The complex singlet potential energy surface of the CHFN 2 O system is investigated at the QCISD(T)/ 6-311G(d,p)//B3LYP/6-31G(d,p) level in order to explore the possible reaction mechanism of 1 CHF radical with N 2 O. Twenty-eight minimum isomers and sixty-four transition states are located. For the most relevant reaction pathways, the high-level QCISD(T)/6-311G(2df,p) single-point calculations are performed at the MP2/6-311G(d,p) geometries to accurately determine the energetics. In various possible initial association ways, the end-N attack leading to HFCN 2 O a 1 is the most feasible pathway with the barrier of 13.5 kcal/mol, whereas for the other attack ways, each involves a higher barrier and thus may not be of significance even at very high temperatures. Starting from HFCN 2 O a, the most favorable reaction pathway is the almost barrierless dissociation of trans-HFCN 2 O a leading to product P 1 HFCN+NO via the direct N-N bond cleavage. A comparable pathway is the ring-closure of cis-HFCN 2 O a 3 leading to four-membered ring isomer b followed by the direct dissociation to P 4 N 2 +HFCO. The less and least competitive pathways are the concerted F-shift and N-N bond rupture to P 2 HCN+FNO as well as the concerted H-shift and N-N bond cleavage to P 3 FCN+HNO, respectively. However, these primary products P 1 , P 2 . P 3 , and P 4 cannot further dissociate due to thermodynamical and kinetic factors. By comparison, it is found that the B3LYP-calculated and MP2-calculated results are generally in agreement. In addition, the discrepancies and similarity between the title reaction and analogous 1 CH 2 +N 2 O reaction are discussed. The present paper may assist in future experimental identification of the product distributions for the title reaction and may be helpful for understanding the halogenated carbene chemistry.

The complex triplet potential energy surface of the CH 2 N 2 O system, including 49 minimum isomers and 114 transition states, is investigated at the B3LYP and QCISD(T) (single-point) levels in order to explore the possiblereaction mechanism of the 3 CH 2 radical with N 2 O. The most feasible pathway is the head-on attack of 3 CH 2 at the terminal N-atom of N 2 O to form cis-H 2 CNNO (a 1 ) and trans-H 2 CNNO (a 2 ). Both a 1 and a 2 can subsequently dissociate to give P 1 (H 2 CN + NO) via the direct N-N bond rupture. Much less competitively, a 1 can undergo a 1,4-H shift, leading to the chainlike isomer HCNNOH (k 1 ), followed by the direct N-N bond cleavage to form product P 2 (HCN + 3 HON) or interconversion between the isomers k 1 -k 8 and subsequent dissociation to P 2 . Furthermore, the products P 1 (H 2 CN + NO) and P 2 (HCN + 3 HON) can undergo secondary dissociation to the same product P 1 2 (HCN + NO + H). The formation of CO, however, seems impossible due to rather large barriers. Our results are in part contradictory with the recent time-resolved Fourier transform infrared spectroscopic study that nascent vibrationally excited products CO, NO, and HCN were observed. Since the initial N-attack step from R to a 1 needs a considerable barrier of 14.8 kcal/mol, the title reaction may only be significant at high temperatures, as confirmed by the ab initio dynamic calculations on the rate constants. The reactivity discrepancies between the triplet and singlet CH 2 with N 2 O are compared and discussed in terms of their potential energy surface features. Our calculations suggest that future experimental reinvestigations on the product distributions and rate constants of the title reaction at high temperatures are greatly desired.

The dynamical properties of the hydrogen abstraction reactions from halomethanes of CHCl 3 - n F n (n = 0-2) and CH 2 Cl 2 with Cl atoms in the temperature range 200-700 K are investigated theoretically. The minimum energy paths (MEPs) of these reactions are calculated at the BH&H-LYP/6-31 1G(d,p) level, and the energies along the MEPs are further refined at the QCISD(T)/6-311 + G(d,p) (single-point) level. For the title reactions, the theoretical rate constants by using improved canonical variational transition state theory incorporating small-curvature tunneling correction are in good agreement with available experimental results. It is shown that the vibrational adiabatic potential energy curves for these reactions have two barriers, a situation similar to the analogous CH 3 X + Cl (X = F, Cl, Br) reaction. For these reactions, the small-curvature tunneling effects are found to be small and the variational effects except for the CHCl 3 + Cl reaction are found to be small over the temperature range considered.

A detailed theoretical survey on the triplet potential energy surface (PES) for the CH + NO2 reaction is carried out at the B3LYP and CCSD(T) (single-point) levels in order to gain a deeper mechanistic knowledge of this important radical reaction. Thirty-eight minimum isomers and 107 transition states are located. It is shown that the CH and NO2 radicals can be brought together barrierlessly via the triplet PES to form the initial N-attack adduct HCNO2 (1) that lies 50.6 kcal/mol below the reactant R. Subsequently, the most feasible channel is the direct O-extrusion of 1 to produce P6 (HCNO + 3O) with the barrier 31.2 kcal/mol. The less competitive channel is a 1,3-H shift conversion of 1 to the branched isomer HON(O)C (10) (34.2 kcal/mol below R) with a barrier 37.1 kcal/mol, which can directly dissociate to product P9 (CNO + OH) with a small barrier 9.0 kcal/mol. However, the oxygen-shift conversion of 1 leading to the very low lying isomers OC(H)NO (2) (2‘) that can directly dissociate to P1 (HCO + NO)...

B3LYP/6-311G(d,p), MP2/6-311G(d,p) and CCSD(T)/6-311+G(2d,2p) (single-point) methods are employed to investigate the doublet potential-energy surface of the C2H+H2O radical reaction. It is shown that the quasi-direct hydrogen abstraction leading to product C2H2+OH is kinetically much more competitive than other dissociation or association−elimination processes. Further higher-level CCSD(T)/6-311+G(3df,2p)//QCISD/6-311G(d,p)+ZPVE calculation predicts this simple H-abstraction process to possess a classical barrier height of 3.7 kcal/mol, which is larger than those for the C2H+H2 and C2H+CH4 reactions. The calculated rate constants of the direct hydrogen abstraction process indicate that the title reaction is very slow near room temperature and may be of less importance than previously expected. Our results show that the C2H+H2O radical reaction is a normal quasi-direct hydrogen abstraction process in keeping with the Polanyi−Evans type correlation between the k (295 K) value and the H−X bond dissociation e...

A direct dynamics study is carried out for the hydrogen abstraction reaction OH + HBr → H2O + Br with a small barrier. The geometries and frequencies of all the stationary points are optimized by means of the three different methods, i.e., MP2/6-311G(d), BHLYP/6-311+G(d,p), and MP4SDQ/6-311G(d,p). It is shown that at the reactant side, there is a hydrogen-bonded complex (HBC) with an energy less than that of the reactants, and from the HBC to the products, the reaction system passes through a reactant-like transition state with an energy slightly higher than that of the reactants. To improve the reaction enthalpy and potential barrier, higher-level energies for the stationary points are made at the PMP4/6-311++G(3df,3pd) and CCSD(T)/6-311+G(2df,2p) levels. The potential energy profile is further refined by performing the CCSD(T) single-point energy calculations along the minimum-energy path (MEP) at the MP4SDQ level. Furthermore, the rate constants and activation energies over a wide range of temperatures...

Density functional theory (DFT) and ab initio direct dynamics methods have been used to study three hydrogen abstraction reactions of SiH4-n(CH3)n + H → SiH3-n(CH3)n + H2, n = 1−3. For all the reactions, the potential energy surface information is calculated at the DFT BHLYP/6-311+G** level, and energies along the minimum energy path are improved by a series of single-point ab initio PMP4/6-311+G(3df,2p)//BHLYP calculations. Changes of geometries, generalized normal-mode vibrational frequencies, and potential energies along the reaction path of the reactions are discussed and compared. The rate constants of the reactions are calculated by canonical variational transition state theory with the small-curvature tunneling correction (CVT/SCT) method in the temperature range 290−3000 K. Good agreement with experimental values is found for rate constants over the measured temperature ranges. The results show that the variational effect is small and, in the lower temperature range, the small curvature tunneling ...