Ab initio chemical kinetics for the OH+HNCN reaction

The kinetics and mechanism of the reaction of the cyanomidyl radical (HNCN) with the hydroxyl radical (OH) have been investigated by ab initio calculations with rate constants prediction. The single and triplet potential energy surfaces of this reaction have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df,2p) level based on geometries optimized at the B3LYP/6-311+G(3df,2p) and CCSD/6-311++G(d,p) levels. The rate constants for various product channels in the temperature range of 300-3000 K are predicted by variational transition-state and Rice-Ramsperger-Kassel-Marcus (RRKM) theories. The predicted total rate constants can be represented by the expressions ktotal=2.66 x 10(+2)xT-4.50 exp(-239/T) in which T=300-1000 K and 1.38x10(-20)xT2.78 exp(1578/T) cm3 molecule(-1) s(-1) where T=1000-3000 K. The branching ratios of primary channels are predicted: k1 for forming singlet HON(H)CN accounts for 0.32-0.28, and k4 for forming singlet HONCNH accounts for 0.68-0.17 in the temperature range of 300-800 K. k2+k7 for producing H2O+NCN accounts for 0.55-0.99 in the high-temperature range of 800-3000 K. The branching ratios of k3 for producing HCN+HNO, k6 for producing H2N+NCO, k8 for forming 3HN(OH)CN, k9 for producing CNOH+3NH, and k5+k10 for producing NH2+NCO are negligible. The rate constants for key individual product channels are provided in a table for different temperature and pressure conditions.     

Atmospheric reaction of the HOSO radical with NO2: a theoretical study

The gas-phase reaction between HOSO and NO(2) was examined using density functional theory. Geometry optimizations and frequency computations were performed at the B3LYP/6-311++G(2df,2pd) level of theory for all minimum species and transition states. The ground-state potential energy surface, including activation energies and enthalpies, were calculated using the ab initio CBS-QB3 composite method. The results suggest that the addition of HOSO and NO(2) leads to two possible intermediates, HOS(O)NO(2) and HOS(O)ONO, without any energy barrier. The HOS(O)NO(2) easily decomposes into HONO + SO(2) through the low energy product complex HONO···SO(2), whereas the HOS(O)ONO dissociates to HOSO(2) + NO products. This latter dissociation is preferred from the isomerization of the HOS(O)ONO to HOS(NO)O(2). Also, HOS(O)NO(2) isomerization to HOS(O)ONO is hindered due to the presence of a large energy barrier. From the thermodynamic aspect, the main products in the title reaction are HONO + SO(2), whereas HOSO(2) + NO are expected as a minor products.     

Ab initio chemical kinetics for the ClOO + NO reaction: effects of temperature and pressure on product branching formation

The kinetics and mechanism for the reaction of ClOO with NO have been investigated by ab initio molecular orbital theory calculations based on the CCSD(T)/6-311+G(3df)//PW91PW91∕6-311+G(3df) method, employed to evaluate the energetics for the construction of potential energy surfaces and prediction of reaction rate constants. The results show that the reaction can produce two key low energy products ClNO + (3)O(2) via the direct triplet abstraction path and ClO + NO(2) via the association and decomposition mechanism through long-lived singlet pc-ClOONO and ClONO(2) intermediates. The yield of ClNO + O(2) ((1)△) from any of the singlet intermediates was found to be negligible because of their high barriers and tight transition states. As both key reactions initially occur barrierlessly, their rate constants were evaluated with a canonical variational approach in our transition state theory and Rice-Ramspergen-Kassel-Marcus/master equation calculations. The rate constants for ClNO + (3)O(2) and ClO + NO(2) production from ClOO + NO can be given by 2.66 × 10(-16) T(1.91) exp(341/T) (200-700 K) and 1.48 × 10(-24) T(3.99) exp(1711/T) (200-600 K), respectively, independent of pressure below atmospheric pressure. The predicted total rate constant and the yields of ClNO and NO(2) in the temperature range of 200-700 K at 10-760 Torr pressure are in close agreement with available experimental results.     

Theoretical study on the reaction mechanism of NH2(-) with O2 (a1Δg)

A detailed theoretical study of the potential energy surface of poorly understood ion-molecule reaction of NH(2)(-) and O(2) (a(1)Δ(g)) is explored at the density functional theory B3LYP/6-311++G(d,p), ab initio of QCISD/6-311++G(d,p) and CCSD(T)/6-311++G(3df, 2pd) (single-point) theoretical levels for the first time. It is shown that there are six total possible products from P(1) to P(6) on the singlet potential energy surface. Among these, the charge-transfer product P(1) (NH(2) + O(2)(-)) is the most favorable product with predominant abundances, whereas P(4) (NO(-) + H(2)O) and P(2) (HNO + OH(-)) may be the second and third feasible products followed by the almost neglectable P(3) (NO(2)(-) + H(2)), while P(5) (c-NO(2)(-) + H(2)) and P(6) (ONO(-) + H(2)) will not be observed due to their either high barriers or being secondary products. The present theoretical study points out that besides P(1) (NH(2) + O(2)(-)) and P(2) (HNO + OH(-)), P(4) (NO(-) + H(2)O) should be also observed, which is different from the previous experiment study by Anthony Midey et al. in 2008. In addition, almost all of the reaction pathways to products are exothermic and the reaction rate should be very fast since the reaction barriers are very low except for P(5) (c-NO(2)(-) + H(2)) which is in agreement with the measured total reaction rate constant k = 9.0 × 10(-10) cm(3)s(-1) at 300 K in the experiment study. It is expected that the present theoretical study may be helpful for the understanding of the reaction mechanism related to NHX(-), NX(2)(-), PHX(-), and PX(2)(-) (X = H, F, and Cl).     

CH3与NO2的反应

The elementary reaction of the CH3 radical with NO2 was investigated by time-resolved FTIR spectroscopy and quantum chemical calculations. The CH3 radical was produced by laser photolysis of CH3Br or CH3I at 248 nm. Vibrationally excited products OH, HNO and CO2 were observed by the time-resolved spectroscopy for the first time. The formation of another product NO was also verified. According to these observations, the product channels leading to CH3O+NO, CH2NO+OH and HNO+H2CO were identified. The channel of CH3O+NO was the major one. The reaction mechanisms of the above channels were studied by quantum chemical calculations at CCSD(T)/6-311++G(df,p)//MP2/6-311G(d,p) level. The calculated results fit with the experimental observations well.     

Ab initio study of the ClO + NH2 reaction: prediction of the total rate constant and product branching ratios

The mechanism for ClO + NH2 has been investigated by ab initio molecular orbital and transition-state theory calculations. The species involved have been optimized at the B3LYP/6-311+G(3df,2p) level and their energies have been refined by single-point calculations with the modified Gaussian-2 method, G2M(CC2). Ten stable isomers have been located and a detailed potential energy diagram is provided. The rate constants and branching ratios for the low-lying energy channel products including HCl + HNO, Cl + NH2O, and HOCl + 3NH (X(3)Sigma(-)) are calculated. The result shows that formation of HCl + HNO is dominant below 1000 K; over 1000 K, Cl + NH2O products become dominant. However, the formation of HOCl + 3NH (X(3)Sigma(-)) is unimportant below 1500 K. The pressure-independent individual and total rate constants can be expressed as k1(HCl + HNO) = 4.7 x 10(-8)(T(-1.08)) exp(-129/T), k(2)(Cl + NH2O) = 1.7 x 10(-9)(T(-0.62)) exp(-24/T), k3(HOCl + NH) = 4.8 x 10(-29)(T5.11) exp(-1035/T), and k(total) = 5.0 x 10(-9)(T(-0.67)) exp(-1.2/T), respectively, with units of cm(3) molecule(-1) s(-1), in the temperature range of 200-2500 K.     

Quantum chemical prediction of pathways and rate constants for reaction of cyanomethylene radical with NO

High-level ab initio calculations have been performed to study the mechanism and kinetics of the reaction of the cyanomethylene radical (HCCN) with the NO. The species involved have been optimized at the B3LYP/6-311++G(3df,2p) level, and their corresponding single-point energies are improved by the CCSD(T)/aug-cc-PVQZ//B3LYP/6-311++G(3df,2p) approach. From the calculated potential energy surface, we have predicted the favorable pathways for the formation of several isomers of a HCCN-NO complex. Barrierless formation of HCN + NCO (P1) is also possible. Formation of HCNO + CN (P3) is endoergic but may become significant at high temperatures. To rationalize the scenario of our calculated results, we also employ the Fukui functions and hard-and-soft acid-and-base (HSAB) theory to seek possible clues. The predicted total rate coefficient, k(total), at He pressure 760 Torr can be represented with the equation k(total) = 1.40 × 10(-7) T(-2.01) exp(3.15 kcal mol(-1)/RT) at T = 298-3000 K in units of cm(3) molecule(-1) s(-1). The predicted total rate coefficients at some available conditions (He pressures of 6, 18, and 30 Torr in the temperature of 298 K) are in reasonable agreement with experimental observation. In addition, the rate constants for key individual product channels are provided in different temperature and pressure conditions.     

n(H_2O)(n=1,2)在HO_2+NO→HNO_3反应中的催化机制研究

采用CCSD(T)/aug-cc-p VTZ//B3LYP/6-311+G(2df,2p)方法对n(H_2O)(n=0,1,2)参与HO_2+NO→HNO_3反应的微观机理和速率常数进行了研究.结果表明,由于水分子与HO_2形成的复合物(H_2O…HO_2,HO_2…H_2O)结合NO与水分子形成的复合物(NO…H_2O,ON…H_2O)的反应方式具有较高能垒和较低有效速率,其对HO_2+NO→HNO_3反应的影响远小于双体水(H_2O)2与HO_2(或NO)形成复合物然后再与另一分子反应物NO(或HO_2)的反应方式,因此n(H_2O)(n=1,2)催化HO_2+NO→HNO_3反应主要经历了HO_2…(H_2O)_n(n=1,2)+NO和NO…(H_2O)_n(n=1,2)+HO_22种反应类型.由于HO_2…(H_2O)_n(n=1,2)+NO反应的低能垒和高速率,HO_2…(H_2O)_n(n=1,2)+NO反应优于NO…(H_2O)_n(n=1,2)+HO_2反应.与此同时,由于计算温度范围内HO_2…H_2O+NO反应的有效速率常数比HO_2…(H_2O)2+NO反应对应的有效速率常数大了10~12数量级,可推测(H_2O)_n(n=1,2)催化HO_2+NO→HNO_3反应主要来自于单个水分子.此外,在216.7~298.6 K范围内水分子对HO_2+NO→HNO_3反应起显著的正催化作用,且随温度的升高有明显增大的趋势,在298.2 K时增强因子k'RW1/ktotal达到67.93%,表明在实际大气环境中水蒸气对HO_2+NO→HNO_3反应具有显著影响.     

CH2SH与NO2双自由基反应机理的理论研究

在B3LYP/6-311＋＋G(2df,p)水平上优化了标题反应驻点物种的几何构型, 并在相同水平上通过频率计算和内禀反应坐标(IRC)分析对过渡态结构及连接性进行了验证. 采用双水平计算方法HL//B3LYP/6-311＋＋G(2df,p)对所有驻点及部分选择点进行了单点能校正, 构建了CH2SH＋NO2反应体系的单重态反应势能剖面. 研究结果表明, CH2SH与NO2反应体系存在4条主要反应通道, 两个自由基中的C与N首先进行单重态耦合, 形成稳定的中间体HSCH2NO2 (a). 中间体a经过C—N键断裂和H(1)—O(2)形成过程生成主要产物P1 (CH2S＋trans-HONO), 此过程需克服124.1 kJ•mol－1的能垒. 中间体a也可以经过C—N键断裂及C—O键形成转化为中间体HSCH2ONO (b), 此过程的能垒高达238.34 kJ•mol－1. b再经过一系列的重排异构转化得到产物P2 (CH2S＋cis-HONO), P3 (CH2S＋HNO2)和P4 (SCH2OH＋NO). 所有通道均为放热反应, 反应能分别为－150.37, －148.53, －114.42和－131.56 kJ•mol－1. 标题反应主通道R→a→TSa/P1→P1的表观活化能为－91.82 kJ•mol－1, 此通道在200～3000 K温度区间内表观反应速率常数三参数表达式为kCVT/SCT＝8.3×10－40T4.4 exp(12789.3/T) cm3•molecule－1•s－1.     

Ab initio chemical kinetics for reactions of ClO with Cl2O2 isomers

The mechanisms for the reactions of ClO with ClOClO, ClOOCl, and ClClO(2) have been investigated at the CCSD(T)/6-311+G(3df)//PW91PW91∕6-311+G(3df) level of theory. The rate constants for their low energy channels have been calculated by statistical theory. The results show that the main products for the reaction of ClO with ClOClO are ClOCl + ClOO, which can be produced readily by ClO abstracting the terminal O atom from ClOClO. This process occurs without an intrinsic barrier, with the predicted rate constant: k (ClO + ClOClO) = 7.26 × 10(-10) T(-0.15) × exp (-40/T) cm(3)molecule(-1)s(-1) for 200-1500 K. For the reactions of ClO + ClOOCl and ClClO(2), the lowest abstraction barriers are 7.2 and 7.3 kcal/mol, respectively, suggesting that these two reactions are kinetically unimportant in the Earth's stratosphere as their rate constants are less than 10(-14) cm(3)molecule(-1)s(-1) below 700 K. At T = 200-1500 K, the computed rate constants can be represented by k (ClO+ ClOOCl) = 1.11 × 10 (-14) T (0.87) exp (-3576/T) and k (ClO+ ClClO(2)) = 4.61 × 10(-14) T(0.53) exp (-3588/T) cm(3)molecule(-1)s(-1). For these systems, no experimental or theoretical kinetic data are available for comparison.     

Theoretical studies on the unimolecular decomposition of ethylene glycol

The unimolecular decomposition processes of ethylene glycol have been investigated with the QCISD(T) method with geometries optimized at the B3LYP/6-311++G(d,p) level. Among the decomposition channels identified, the H(2)O-elimination channels have the lowest barriers, and the C-C bond dissociation is the lowest-energy dissociation channel among the barrierless reactions (the direct bond cleavage reactions). The temperature and pressure dependent rate constant calculations show that the H(2)O-elimination reactions are predominant at low temperature, whereas at high temperature, the direct C-C bond dissociation reaction is dominant. At 1 atm, in the temperature range 500-2000 K, the calculated rate constant is expressed to be 7.63 × 10(47)T(-10.38) exp(-42262/T) for the channel CH(2)OHCH(2)OH → CH(2)CHOH + H(2)O, and 2.48 × 10(51)T(-11.58) exp(-43593/T) for the channel CH(2)OHCH(2)OH → CH(3)CHO + H(2)O, whereas for the direct bond dissociation reaction CH(2)OHCH(2)OH → CH(2)OH + CH(2)OH the rate constant expression is 1.04 × 10(71)T(-16.16) exp(-52414/T).     

Kinetics of the NCCO + NO2 reaction

The kinetics of the NCCO + NO(2) reaction was studied by transient infrared laser absorption spectroscopy. The total rate constant of the reaction was measured to be k = (2.1 ± 0.1) × 10(-11) cm(3) molecule(-1) s(-1) at 298 K. Detection of products and consideration of possible secondary chemistry shows that CO(2) + NO + CN is the primary product channel. The rate constants of the NCCO + CH(4) and NCCO + C(2)H(4) reactions were also measured, obtaining upper limits of k (NCCO + CH(4)) ≤ 7.0 × 10(-14) cm(3) molecule(-1) s(-1) and k (NCCO + C(2)H(4)) ≤ 5.0 × 10(-15) cm(3) molecule(-1) s(-1). Ab initio calculations on the singlet and triplet potential energy surfaces at B3LYP/6-311++G**//CCSD(T)/6-311++G** levels of theory show that the most favorable reaction pathway occurs on the singlet surface, leading to CO(2) + NO + CN products, in agreement with experiment.     

Heterogeneous chemistry of the NO3 free radical and N2O5 on decane flame soot at ambient temperature: reaction products and kinetics

The interaction of NO3 free radical and N2O5 with laboratory flame soot was investigated in a Knudsen flow reactor at T = 298 K equipped with beam-sampling mass spectrometry and in situ REMPI detection of NO2 and NO. Decane (C10H22) has been used as a fuel in a co-flow device for the generation of gray and black soot from a rich and a lean diffusion flame, respectively. The gas-phase reaction products of NO3 reacting with gray soot were NO, N2O5, HONO, and HNO3 with HONO being absent on black soot. The major loss of NO3 is adsorption on gray and black soot at yields of 65 and 59%, respectively, and the main gas-phase reaction product is N2O5 owing to heterogeneous recombination of NO3 with NO2 and NO according to NO3 + {C} --> NO + products. HONO was quantitatively accounted for by the interaction of NO2 with gray soot in agreement with previous work. Product N2O5 was generated through heterogeneous recombination of NO3 with excess NO2, and the small quantity of HNO3 was explained by heterogeneous hydrolysis of N2O5. The reaction products of N2O5 on both types of soot were equimolar amounts of NO and NO2, which suggest the reaction N2O5 + {C} --> N2O3(ads) + products with N2O3(ads) decomposing into NO + NO2. The initial and steady-state uptake coefficients gamma 0 and gamma ss of both NO3 and N2O5 based on the geometric surface area continuously increase with decreasing concentration at a concentration threshold for both types of soot. gamma ss of NO3 extrapolated to [NO3] --> 0 is independent of the type of soot and is 0.33 +/- 0.06 whereas gamma ss for [N2O5] --> 0 is (2.7 +/- 1.0) x 10(-2) and (5.2 +/- 0.2) x 10(-2) for gray and black soot, respectively. Above the concentration threshold of both NO3 and N2O5, gamma ss is independent of concentration with gamma ss(NO3) = 5.0 x 10(-2) and gamma ss(N2O5) = 5.0 x 10(-3). The inverse concentration dependence of gamma below the concentration threshold reveals a complex reaction mechanism for both NO3 and N2O5. The atmospheric significance of these results is briefly discussed.     

Ab initio studies of CIO, reactions: prediction of the rate constants of CIO + NO for the forward and reverse processes.

The mechanisms for ClO+NO and its reverse reactions were investigated by means of ab initio molecular orbital and statistical theory calculations. The species involved were optimized at the B3LYP/6-311 +G(3df) level, and their energies were refined at the CCSD(T)/6-311+ G(3df)//B3LYP/6-311 + G(3df) level. Five isomers and the transition states among them were located. The relative stability of these isomers is ClNO2 > cis-ClONO > trans-ClONO > cis-OClNO>trans-OClNO. The heats of formation of the three most-stable isomers were predicted using isodesmic reactions by different methods. The predicted bimolecular reaction rate constant shows that, below 100 atm, the formation of Cl+NO2 is dominant and pressure-independent. The total rate constant can be expressed as: k(ClO+NO)= 1.43 x 10(-9)T(-083)exp(92/ T) cm3 molecule(-1)s(-1) in the temperature range of 200-1000 K, in close agreement with experimental data. For the reverse reaction, Cl+NO2-->ClNO2 and ClONO (cis and trans isomers), the sum of the predicted rate constants for the formation of the three isomers and their relative yields also reproduce the experimental data well. The predicted total third-order rate constants in the temperature range of 200-1000 K can be represented by: k0(He) = 4.89 x 10(-6)T(-5.85) exp(-796/T) cm6 molecule(-1)s(-1) and k0(N2) =5.72 x 10(-15)T(-5.80) exp(-814/T) cm6 molecule(-1)s(-1). The predicted high- and low-pressure limit decomposition rates of CINO2 in Ar in the temperature range 400-1500 K can be expressed, respectively, by: k-(ClNO2) = 7.25 x 10(19)T(-1.89) exp(-16875/T) s(-1) and kd(ClNO2) = 2.51 x 10(38)T(-6.8) exp(-18409/T) cm3 molecule(-1) s(-1). The value of k0(ClNO2) is also in reasonable agreement with available experimental data.     

Unimolecular decomposition of ethyl hydroperoxide: ab initio/Rice-Ramsperger-Kassel-Marcus theoretical prediction of rate constants

Alkyl hydroperoxides are found to be important intermediates in the combustion and oxidation processes of hydrocarbons. However, studies of ethyl hydroperoxide (CH(3)CH(2)OOH) are limited. In this work, kinetics and mechanisms for unimolecular decomposition of CH(3)CH(2)OOH have been investigated. The potential energy surface of decomposition reactions have first been predicted at the CCSD(T)/6-311+G(3df,2p)//B3LYP/6-311G(d,p) level. The results show that the formation of CH(3)CH(2)O + OH via O-O direct bond dissociation is dominant, the branching ratio of which is over 99% in the whole temperature range from 300 to 1000 K, and its rate constant can be expressed as k1 = 9.26 × 10(52)T(-11.91)exp(-26879/T) s(-1) at 1 atm. The rate constants of the reaction CH(3)CH(2)OOH → CH(3)CH(2)O + OH at different temperatures and pressures have been calculated, which can help us to comprehend the reactions of CH(3)CH(2)OOH at experimental conditions.     

Ab initio kinetics of the reaction of HCO with NO: abstraction versus association/elimination mechanism

The kinetics and mechanism for the reaction of HCO with NO occurring by both singlet and triplet electronic state potential-energy surfaces (PESs) have been studied at the modified Gaussian-2 level of theory based on the geometric parameters optimized by the Becke-3 Lee-Yang-Parr/6-311G(d,p) method. There are two major reaction channels on both singlet and triplet PESs studied: one is direct H abstraction producing CO+HNO and the other is association forming a stable HC(O)NO (nitrosoformaldehyde) molecule. The dominant reaction is predicted to be the direct H abstraction occurring primarily by the lowest-energy path via a loose hydrogen-bonding singlet molecular complex, ON...HCO, with a 2.9-kcal/mol binding energy and a small decomposition barrier (1.9 kcal/mol). The commonly assumed HC(O)NO intermediate, predicted to lie below the reactants by 27.7 kcal/mol, has a high HNO-elimination barrier (34.5 kcal/mol). Bimolecular rate constants for the formation of the singlet products and their branching ratios have been calculated in the temperature range of 200-3000 K. The rate constant for the disproportionation process producing HNO+CO, found to be affected strongly by multiple reflections above the well of the complex at low temperature, is predicted to be k(HNO)=3.08 x 10(-12) T(0.10) exp(242T) for 200-500 K, and 1.72 x 10(-16) T(1.47) exp(888T) for 500-3000 K in units of cm(3) molecule(-1) s(-1). The high- and low-pressure rate constants for the association process forming HC(O)NO can be represented by k(infinity)=4.42 x 10(-11) T(0.25) exp(-28T) cm(3) molecule(-1) s(-1) (200-3000 K) and k(0)=7.30x10(-16) T(-5.75) exp(-719T) (200-1000 K) and 1.82 x 10(2) T(-11.92) exp(1846T) (1000-3000 K) cm(6) molecule(-2) s(-1) for N(2)-buffer gas. The absolute values of total rate constant, predicted to be weakly dependent negatively on temperature but positively on pressure, are in close agreement with most experimental data within their reported errors.     

Theoretical study and rate constant computation on the reaction HFCO + OH --> CFO + H2O

The potential energy surface, including the geometries and frequencies of the stationary points, of the reaction HFCO + OH is calculated using the MP2 method with 6-31+G(d,p) basis set, which shows that the direct hydrogen abstraction route is the most dominating channel with respect to addition and substitution channels. For the hydrogen abstraction reaction, the single-point energies are refined at the QCISD(T) method with 6-311++G(2df,2pd) basis set. The calculated standard reaction enthalpy and barrier height are -17.1 and 4.9 kcal mol(-1), respectively, at the QCISD(T)/6-311++G(2df,2pd)//MP2/6-31+G(d,p) level of theory. The reaction rate constants within 250-2500 K are calculated by the improved canonical variational transition state theory (ICVT) with small-curvature tunneling (SCT) correction at the QCISD(T)/6-311++G(2df,2pd)//MP2/6-31+G(d,p) level of theory. The fitted three-parameter formula is k = 2.875 x 10(-13) (T/1000)1.85 exp(-325.0/T) cm(3) molecule(-1) s(-1). The results indicate that the calculated ICVT/SCT rate constant is in agreement with the experimental data, and the tunneling effect in the lower temperature range plays an important role in computing the reaction rate constants.     

FC(O)O自由基与NO2反应的量子化学研究

用量子化学DFT, MP2, G3和G3MP2方法对FC(O)O自由基与NO₂的反应机理进行了理论研究. 优化了反应势能面上各驻点的几何结构, 通过内禀反应坐标(IRC)计算和振动分析, 确认了反应中的过渡态, 并用过渡态理论(TST)计算了相关反应的速率常数.     

Theoretical Study of Reaction Mechanism of 1-Propenyl Radical with NO

The reaction system of 1-propenyl radical with NO is an ideal model for studying the intermolecular and intramolecular reactions of complex organic free radicals containing C=C double bonds. On the basis of the full optimization of all species with the Gaussian 98 package at the B3LYP/6-311++G** level, the reaction mechanism was elucidated extensively using the vibrational mode analysis. There are seven reaction pathways and five sets of small molecule end products: CH2O+CH3CN, CH2CHCN+H2O, CH3CHO+HCN, CH3CHO+HNC, and CH3CCH+HNO. The channel of C3H5￠+NO→ IM1→TS1→IM2→TS2→IM3→TS3→CH3CHO+HCN is thermodynamically most favorable.     

HCO+NO2反应势能面的理论研究

在B3LYP/6-311G(d,p)和CCSD(T)/6-311G(d,p)水平上给出了HCO+NO₂反应详细的势能面信息.计算结果表明,该反应采用两种无垒进攻方式,分别得到两种加合物H(O)CNO₂和H(O)CONO.找到7种能量低于反应物且合理的产物及相应的反应路径.通过对热力学和动力学的分析,产物HONO+CO(P2,P3),HNO+CO₂(P1)和H+CO₂+NO(P6)的形成更为有利.计算结果同实验相符,且有助于深入了解HCO自由基的化学行为.