Radical reaction C3H+NO: a mechanistic study

Although a number of hydrocarbon radicals including the heavier C(3)-radicals C(3)H(3) and C(3)H(5) have been experimentally shown to deplete NO effectively, no theoretical or experimental attempts have been made on the reactivity of the simplest C(3)-radical towards NO. In this article, we report our detailed mechanistic study on the C(3)H+NO reaction at the Gussian-3//B3LYP/6-31G(d) level by constructing the singlet and triplet electronic state [H,C(3),N,O] potential energy surfaces (PESs). The l-C(3)H+NO reaction is shown to barrierlessly form the entrance isomer HCCCNO followed by the direct O-elimination leading to HCCCN+(3)O on triplet PES, or by successive O-transfer, N-insertion, and CN bond-rupture to generate the product (1)HCCN+CO on singlet PES. The possible singlet-triplet intersystem crossings are also discussed. Thus, the novel reaction l-C(3)H+NO can proceed effectively even at low temperatures and is expected to play an important role in both combustion and interstellar processes. For the c-C(3)H+NO reaction, the initially formed H-cCCC-NO can most favorably isomerize to HCCCNO, and further evolution follows that of the l-C(3)H+NO reaction. Quantitatively, the c-C(3)H+NO reaction can take place barrierlessly on singlet PES, yet it faces a small barrier 2.7 kcal/mol on triplet PES. The results will enrich our understanding of the chemistry of the simplest C(3)-radical in both combustion and interstellar processes, which to date have received little attention despite their importance and available abundant studies on its structural and spectroscopic properties.     

Ab initio study on the oxidation of NCN by O (3P): prediction of the total rate constant and product branching ratios

The reaction of NCN with O is relevant to the formation of prompt NO according to the new mechanism, CH+N2-->cyclic-C(H)NN- -->HNCN-->H+NCN. The reaction has been investigated by ab initio molecular orbital and transition state theory calculations. The mechanisms for formation of possible product channels involved in the singlet and triplet potential energy surfaces have been predicted at the highest level of the modified GAUSSIAN-2 (G2M) method, G2M (CC1). The barrierless association/dissociation processes on the singlet surface were also examined with the third-order Rayleigh-Schr?dinger perturbation (CASPT3) and the multireference configuration interaction methods including Davidson's correction for higher excitations (MRCI+Q) at the CASPT3(6,6)/6-311+G(3df)//UB3LYP/6-311G(d) and MRCI+Q(6,6)/6-311+G(3df)//UB3LYP/6-311G(d) levels. The rate constants for the low-energy channels producing CO+N2, CN+NO, and N(4S)+NCO have been calculated in the temperature range of 200-3000 K. The results show that the formation of CN+NO is dominant and its branching ratio is over 99% in the whole temperature range; no pressure dependence was noted at pressures below 100 atm. The total rate constant can be expressed by: kt=4.23x10(-11) T0.15 exp(17/T) cm3 molecule(-1) s(-1).     

The N3+ reactivity in ionized gases containing sulfur, nitrogen, and carbon oxides.

The N(3)(+) reactivity with SO(2), N(2)O, CO(2), and CO is studied by mass spectrometric techniques under a wide range of pressures from 10(-7) to 10(-4) Torr. The kinetics, reaction mechanism, and role of vibrationally excited ions are investigated by experimental and theoretical methods. Key distinguishing features of the N(3) (+) reactivity are evidenced by comparison to N(+) and N(2)(+) ions, which mainly undergo charge-exchange reactions. The N(+) transfer to SO(2) prompts formation of NO(+) ions and neutral oxides NO and SO. The N(+) transfer to N(2)O also leads to NO(+) ions by a process not allowed by spin conservation rules. In both cases no reaction intermediate is detected, whereas CO(2) and CO are captured to form the very stable NCO(2) (+) and NCO(+) ions. NCO(2)(+) ions are characterized for the first time as strongly bound triplet ions of NOCO and ONCO connectivity. DFT and CCSD(T) computations have been carried out to investigate the structural and energetic features of the NCO(2) (+) species and their formation process.     

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.     

The DFT study on mechanisms for NCO with C2H5 reaction

A detailed investigation has been performed at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311+G(d,p) level for the reaction of NCO with C₂H₅ by constructing singlet and triplet potential energy surfaces (PES). The results show that the title reaction is more favorable on the singlet PES than on the triplet PES. On the singlet PES, the initial addition processes are barrierless and release lots of energy. The dominant channel occurs via the fragmentations of the initial adduct C₂H₅NCO and C₂H₅OCN to form C₂H₄ + HNCO and HOCN, respectively. With higher barrier heights, other products such as CH₄ + HNC + CO, CH₃CHNH + CO, CH₃CH + HNCO, and CH₃CN + H₂ + CO are less competitive. On the triplet PES, the entrance reactions surpass significant barriers; therefore, it could be negligible at the normal atmospheric condition. However, the most feasible channel on the triplet PES is the direct hydrogen abstraction channel to form CH₂CH₂ + HNCO. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical study on the reaction of VS^＋（^3∑^-, 1^Г） with CO

Two possible reaction mechanisms of VS^＋（^3∑^-, 1^Г） with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD（T）/6-311＋G （3df, 3pd） methods： the O/S exchange reaction （VS^＋＋CO→VO^＋＋CS） and the S-transfer reaction （VS^＋ ＋ CO → V^＋ ＋ COS）. The two reactions proceed via two-step and one-step mechanism, respectively. The barriers of the triplet and singlet PESs are 30.6 and 50.9 kcal/mol, respectively, for O/S exchange reaction and 7.3 and 50.2 kcal/mol, respectively, for the S-transfer reaction. The results indicate that the triplet ground state reaction is more favorable, and the S-transfer reaction is more favorable than the O/S exchange reaction, which is in good agreement with the experimental observation.     

New insight into the gas-phase bimolecular self-reaction of the HOO radical

The singlet and triplet potential energy surfaces (PESs) for the gas-phase bimolecular self-reaction of HOO*, a key reaction in atmospheric environments, have been investigated by means of quantum-mechanical electronic structure methods (CASSCF and CASPT2). All the reaction pathways on both PESs consist of a first step involving the barrierless formation of a prereactive doubly hydrogen-bonded complex, which is a diradical species lying about 8 kcal/mol below the energy of the reactants at 0 K. The lowest energy reaction pathway on both PESs is the degenerate double hydrogen exchange between the HOO* moieties of the prereactive complex via a double proton transfer mechanism involving an energy barrier of only 1.1 kcal/mol for the singlet and 3.3 kcal/mol for the triplet at 0 K. The single H-atom transfer between the two HOO* moieties of the prereactive complex (yielding HOOH + O2) through a pathway keeping a planar arrangement of the six atoms involves a conical intersection between either two singlet or two triplet states of A' and A" symmetries. Thus, the lowest energy reaction pathway occurs via a nonplanar cisoid transition structure with an energy barrier of 5.8 kcal/mol for the triplet and 17.5 kcal/mol for the singlet at 0 K. The simple addition between the terminal oxygen atoms of the two HOO* moieties of the prereactive complex, leading to the straight chain H2O4 intermediate on the singlet PES, involves an energy barrier of 7.3 kcal/mol at 0 K. Because the decomposition of such an intermediate into HOOH + O2 entails an energy barrier of 45.2 kcal/mol at 0 K, it is concluded that the single H-atom transfer on the triplet PES is the dominant pathway leading to HOOH + O2. Finally, the strong negative temperature dependence of the rate constant observed for this reaction is attributed to the reversible formation of the prereactive complex in the entrance channel rather than to a short-lived tetraoxide intermediate.     

Theoretical study on reaction mechanism of the cyanogen radical with nitrogen dioxide

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.     

A theoretical study of the mechanism and kinetics of F+N3 reactions.

Both the singlet(1A') and triplet(3A') potential energy surfaces (PESs) of F+N(3) reactions are investigated using the complete-active-space self-consistent field (CASSCF) and the multireference configuration interaction (MRCI) methods with a proper active space. The minimum energy crossing point (MECP) at the intersection seam between the 1A' and 3A' PESs is located and used to clarify the reaction mechanisms. Two triplet transition states are found, with one in the cis form and the other one in the trans form. Further kinetic calculations are performed with the canonical unified statistical (CUS) theory on the singlet PES and the improved canonical variational transition-state (ICVT) method on the triplet PES. The rate constants are also reported. At 298 K, the calculated rate constant is in reasonably good agreement with experimental values, and spin-orbit coupling effects lower it by 28 %. The spectroscopic constants derived from the fitted potential-energy curves for the singlet and triplet states of NF are in very good agreement with experimental values. Our calculations indicate that the adiabatic reaction on the singlet PES leading to NF(a(1)Delta)+N(2) is the major channel, whereas the nonadiabatic reaction through the MECP, which leads to NF(X(3)Sigma(-))+N(2), is a minor channel.     

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.     

A theoretical study of the reaction of N(4 S) with nitrogen dioxide on the N2O2 potential energy surface

The reaction of N(⁴ S) radical with NO₂ molecule has been studied theoretically using density functional theory and ab initio quantum chemistry method. Both singlet and triplet electronic state [N₂O₂] potential energy surfaces (PESs) are calculated at the G3B3 level of theory. Also, the highly cost-expensive coupled-cluster theory including single and double excitations and perturbative inclusion of triple excitations CCSD(T)/cc-pVTZ single-point energy calculation is performed on the basis of the geometries obtained at the Becke??s three parameter Lee-Yang-Parr B3LYP/6-311++G(d, p) level. On the singlet PES of the title reaction, it is shown that the most feasible pathway should be as follows. The atomic radical N attacking the NO bond of the NO₂ molecule first to form the adduct 1 N(NO)O, followed by one of the NO bond broken to give intermediate 2 ONNO, and then to the major products P1 (2NO). On the triplet PES of the title reaction, it is shown that the most favorable pathway should be the atomic radical N attacking the N-atom of NO₂ firstly to form the adduct 7 NN(OO), followed by one of the NO bonds breaking to give intermediate 8 NNOO, and then leading to the major products P2 (O₂ + N₂). As efficient routes to the reduction of NO₂ to form N₂ and O₂ are sought, both kinetic and thermodynamic considerations support the viability of this channel. All the involved transition states for generation of (2NO), (³O + N₂O), and (O₂ + N₂) lie much lower than the reactants. Thus, the novel reaction N + NO₂ can proceed effectively even at low temperatures and it is expected to play a role in both combustion and interstellar processes. The other reaction pathways are less competitive due to thermodynamical or kinetic factors. On the basis of the analysis of the kinetics of all path-ways through which the reactions proceed, we expect that the competitive power of reaction pathways may vary with experimental conditions for the title reaction. The calculated reaction heats of formation are in good agreement with that obtained experimentally.     

Singlet and triplet potential surfaces for the O2+C2H4 reaction

Electronic structure calculations at the CASSCF and UB3LYP levels of theory with the aug-cc-pVDZ basis set were used to characterize structures, vibrational frequencies, and energies for stationary points on the ground state triplet and singlet O(2)+C(2)H(4) potential energy surfaces (PESs). Spin-orbit couplings between the PESs were calculated using state averaged CASSCF wave functions. More accurate energies were obtained for the CASSCF structures with the MRMP2/aug-cc-pVDZ method. An important and necessary aspect of the calculations was the need to use different CASSCF active spaces for the different reaction paths on the investigated PESs. The CASSCF calculations focused on O(2)+C(2)H(4) addition to form the C(2)H(4)O(2) biradical on the triplet and singlet surfaces, and isomerization reaction paths ensuing from this biradical. The triplet and singlet C(2)H(4)O(2) biradicals are very similar in structure, primarily differing in their C-C-O-O dihedral angles. The MRMP2 values for the O(2)+C(2)H(4)→C(2)H(4)O(2) barrier to form the biradical are 33.8 and 6.1 kcal/mol, respectively, for the triplet and singlet surfaces. On the singlet surface, C(2)H(4)O(2) isomerizes to dioxetane and ethane-peroxide with MRMP2 barriers of 7.8 and 21.3 kcal/mol. A more exhaustive search of reaction paths was made for the singlet surface using the UB3LYP/aug-cc-pVDZ theory. The triplet and singlet surfaces cross between the structures for the O(2)+C(2)H(4) addition transition states and the biradical intermediates. Trapping in the triplet biradical intermediate, following (3)O(2)+C(2)H(4) addition, is expected to enhance triplet→singlet intersystem crossing.     

Theoretical study on the reaction of CN radicals with ClO radicals by density functional theory

The reaction mechanism of CN radicals with ClO radicals has been studied theoretically using ab initio and density functional theory (DFT). The result shows that the main reaction path is the O atom in radical ClO attacks the C atom in radical CN to compose the intermediate 1 ClOCN. Three thermodynamically accessible prodncts, P₁ (CO+ClN), P₃ (NO+CCl), and P₄ (ClNCO), were obtained from intermediate 1 through isomerization and decomposition reactions. P₄ is the primary product, and P₁ and P₃ are the secondary product. Compared with the singlet potential energy surface, the contribution of the triplet potential energy surface can be ignored.     

Theoretical study on the reaction of VS+(3∑-, 1Γ) with CO

Two possible reaction mechanisms of VS (3Ε-, 1Γ) with CO in the gas phase have been studied by using B3LYP/TZVP and CCSD(T)/6-311 G (3df, 3pd) methods: the O/S exchange reaction (VS CO → VO CS) and the S-transfer reaction (VS CO → V COS). The two reactions proceed via two-step and one-step mechanism, respectively. The barriers of the triplet and singlet PESs are 30.6 and 50.9 kcal/mol, respectively, for O/S exchange reaction and 7.3 and 50.2 kcal/mol, respectively, for the S-transfer reaction. The results indicate that the triplet ground state reaction is more favorable, and the S-transfer reaction is more favorable than the O/S exchange reaction, which is in good agreement with the experimental observation.     

NCO自由基与O和N反应的理论研究

采用密度泛函和量子化学从头算方法, 对NCO自由基和O, N原子反应的势能面进行了理论研究, 讨论了主要的反应通道. 这两种自由基反应的机理比较类似, 初始都有两种进攻方式. NCO与O的主反应通道是O原子从N端无势垒加合, 经过一低垒过渡态, 得到稳定产物P1(CO+NO), 而对NCO与N反应得到了一完整反应通道和无垒加合产物.     

Theoretical study on the mechanism of the (3)CH(2) + NO(2) reaction

The complex doublet potential energy surface of the CH(2)NO(2) system is investigated at the B3LYP/6-31G(d,p) and QCISD(T)/6-311G(d,p) (single-point) levels to explore the possible reaction mechanism of the triplet CH(2) radical with NO(2). Forty minimum isomers and 92 transition states are located. For the most relevant reaction pathways, the high-level QCISD(T)/6-311 + G(2df,2p) calculations are performed at the B3LYP/6-31G(d,p) geometries to accurately determine the energetics. It is found that the top attack of the (3)CH(2) radical at the N-atom of NO(2) first forms the branched open-chain H(2)CNO(2) a with no barrier followed by ring closure to give the three-membered ring isomer cC(H(2))ON-O b that will almost barrierlessly dissociate to product P(1) H(2)CO + NO. The lesser followed competitive channel is the 1,3-H-shift of a to isomer HCN(O)OH c, which will take subsequent cis-trans conversion and dissociation to P(2) OH + HCNO. The direct O-extrusion of a to product P(3) (3)O + H(2)CNO is even much less feasible. Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the title reaction is expected to be rapid, as is consistent with the measured large rate constant at room temperature. Formation of the other very low-lying dissociation products such as NH(2) + CO(2), OH + HNCO and H(2)O + NCO seems unlikely due to kinetic hindrance. Moreover, the (3)CH(2) attack at the end-O of NO(2) is a barrier-consumed process, and thus may only be of significance at very high temperatures. The reaction of the singlet CH(2) with NO(2) is also briefly discussed. Our calculated results may assist in future laboratory identification of the products of the title reaction.     

Theoretical study of the reaction of carbon monoxide with oxygen molecules in the ground triplet and singlet delta states

Quantum chemical calculations were carried out to study the reaction of carbon monoxide with molecular oxygen in the ground triplet and singlet delta states. Transition states and intermediates that connect the reactants with products of the reaction on the triplet and singlet potential energy surfaces were identified on the base of coupled-cluster method. The values of energy barriers were refined by using compound techniques such as CBS-Q, CBS-QB3, and G3. The calculations showed that there exists an intersection of triplet and singlet potential energy surfaces. This fact leads to the appearance of two channels for the triplet CO+O(2)(X(3)Σ(g)(-)) reaction, which produces atomic oxygen in the ground O((3)P) and excited O((1)D) states. The appropriate rate constants of all reaction paths were estimated on the base of nonvariational transition-state theory. It was found that the singlet reaction rate constant is much greater than the triplet one and that the reaction channel CO+O(2)(a(1)Δ(g)) should be taken into consideration to interpret the experimental data on the oxidation of CO by molecular oxygen.     

Theoretical mechanistic study on the reaction of CN radical with HNCN

The mechanism for the reaction of the cyanogen radical (CN) with the cyanomidyl radical (HNCN) has been investigated theoretically. The electronic structure information of the singlet and triplet potential energy surfaces (PESs) is obtained at the B3LYP/6-311+G(3df,2p) level, and the single-point energies are refined at the CCSD(T)/6-311+G(3df,2p) level as well as by multilevel MCG3-MPWB method. The calculations show that the C atom of CN additions to middle- and end-N atoms of HNCN are two barrierless association processes leading to the energy-rich intermediates IM1 HN(CN)CN and IM2 HNCNCN, respectively, on the singlet PES. The higher barriers of the subsequent isomerization and dissociation channels from IM1 and IM2 indicate that these two intermediates, which have considerably thermodynamic and kinetic stability, are the dominant product at high pressure. While at low pressure, the most favorable product is P(2) H + NCNCN, which will be formed from both IM1 and IM2 via direct dissociation processes by the H-N bond rupture, and the secondary feasible product is P(4) HCN + (1) NCN, while P(5) HCCN + N(2) and P(6) HCNC + N(2) are the least competitive products. On the triplet PES, P(14) NCNC + HN may be a comparable competitive product at high temperature. In addition, the comparison between the mechanisms of the CN + HNCN and OH + HNCN reactions is made. The present results will enrich our understanding of the chemistry of the HNCN radical in combustion processes and interstellar space.     

Theoretical study on the gas-phase reaction mechanism between palladium monoxide and methane

The gas-phase reaction mechanism between palladium monoxide and methane has been theoretically investigated on the singlet and triplet state potential energy surfaces (PESs) at the CCSD(T)/AVTZ//B3LYP/6-311+G(2d, 2p), SDD level. The major reaction channel leads to the products PdCH(2) + H(2)O, whereas the minor channel results in the products Pd + CH(3)OH, CH(2)OPd + H(2), and PdOH + CH(3). The minimum energy reaction pathway for the formation of main products (PdCH(2) + H(2)O), involving one spin inversion, prefers to start at the triplet state PES and afterward proceed along the singlet state PES, where both CH(3)PdOH and CH(3)Pd(O)H are the critical intermediates. Furthermore, the rate-determining step is RS-CH(3) PdOH → RS-2-TS1cb → RS-CH(2)Pd(H)OH with the rate constant of k = 1.48 × 10(12) exp(-93,930/RT). For the first C-H bond cleavage, both the activation strain ΔE(≠)(strain) and the stabilizing interaction ΔE(≠)(int) affect the activation energy ΔE(≠), with ΔE(≠)(int) in favor of the direct oxidative insertion. On the other hand, in the PdCH(2) + H(2) O reaction, the main products are Pd + CH(3)OH, and CH(3)PdOH is the energetically preferred intermediate. In the CH(2)OPd + H(2) reaction, the main products are Pd + CH(3)OH with the energetically preferred intermediate H(2)PdOCH(2). In the Pd + CH(3)OH reaction, the main products are CH(2)OPd + H(2), and H(2)PdOCH(2) is the energetically predominant intermediate. The intermediates, PdCH(2), H(2) PdCO, and t-HPdCHO are energetically preferred in the PdC + H(2), PdCO + H(2), and H(2)Pd + CO reactions, respectively. Besides, PdO toward methane activation exhibits higher reaction efficiency than the atom Pd and its first-row congener NiO.     

Kinetics of the NCO + HCNO reaction

The kinetics of the NCO + HCNO reaction were studied using infrared diode laser absorption spectroscopy. The total rate constant was measured to be k(1) = (1.58 +/- 0.20) x 10(-11) cm(3) molecule(-1) s(-1) at 298 K. After detection of products and consideration of secondary chemistry (primarily O + HCNO and CN + HCNO), we conclude that NO + CO + HCN is the major product channel (phi = 0.92 +/- 0.04), with a minor contribution (phi = 0.04 +/- 0.02) from CO2 + HCNN.