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This work presents two new analytical fits of the ground potential energy surface (PES) (3A″) and the first excited PES (3A′) involved in the title reaction, considering the N-abstraction (1) and the O-abstraction (2) reaction channels, and the reverse reaction (−1). The PESs are derived from ab initio electronic structure calculations by means of second-order perturbation theory on a complete active-space self-consistent-field wave function (CASPT2 method). Stationary points and extensive grids of ab initio points (about 5600 points for the 3A″ PES and 4900 points for the 3A′ PES) were fitted along with some diatomic spectroscopic data to better account for the experimental exoergicity. Thermal rate constants were calculated (200–5000 K) for all mentioned reaction processes by means of the variational transition-state theory with the inclusion of a semiclassical tunneling correction. Excellent agreement with the experimental data was observed for reaction (1) and its reverse, within all the temperature r...

This work presents ab initio electronic structure calculations of the two possible N(4S) + NO(X2) abstraction reaction channels on the lowest 3A' and 3A' potential energy surfaces (PESs). Complete active space self-consistent-field (CASSCF) calculations, second-order perturbation calculations (CASPT2) and multireference configuration interaction calculations (MR-CI) based on CASSCF wave functions, along with some coupled cluster (CC) calculations were carried out by using the standard correlation-consistent (cc-pVnZ and aug-cc-pVnZ, n=D,T,Q,5) Dunning's basis sets. It was shown that there was no energy barrier along the minimum energy path in the 3A' PES for the N-abstraction reaction channel. However, an energy barrier (6.74 kcal/mol) was located in the 3A' PES. This energy barrier was considerably smaller than the previously reported MR-CCI value (14.4 kcal/mol). It was established that the N and O 2s electron correlation, neglected in previous studies of these authors, was the main source of this energy decrease. As a result, the present ab initio data will produce larger values of the thermal rate constants at high temperatures. High-energy barriers were found for the O-abstraction reaction channel in both PESs (41.13 and 30.77 kcal/mol for 3A' and 3A', respectively), which agree with the accepted idea that this channel will be only important at high collision energies. Nonetheless, current ab initio results show that this channel will be open at not very high collision energies (e.g., over 30 kcal/mol could take place). Experimental studies on the O-abstraction reaction channel are missing and would be useful to confirm its ab initio expected importance.

We present the conical-intersection quantum dynamics of the nonreactive quenching (NQ) OH(A(2)Σ(+)) + H'((2)S) → OH(X(2)Π) + H'((2)S), exchange (X) OH(A(2)Σ(+)) + H'((2)S) → OH'(A(2)Σ(+)) + H((2)S), exchange-quenching (XQ) OH(A(2)Σ(+)) + H'((2)S) → OH'(X(2)Π) + H((2)S), and reaction (R) OH(A(2)Σ(+)) + H'((2)S) → O((1)D) + H2(X(1)Σg (+)) collisions. We obtain initial-state-resolved reaction probabilities, cross sections, and rate constants by considering OH in the ground vibrational state and in the rotational levels j0 = 0, 1, 2, and 5. Coupled-channel real wavepackets (WPs) on the X̃(1)A(') and B̃(1)A(') coupled electronic states are propagated by using the Dobbyn and Knowles diabatic potential surfaces and coupling [A. J. Dobbyn and P. J. Knowles, Mol. Phys. 91, 1107 (1997) and A. J. Dobbyn and P. J. Knowles, Faraday Discuss. 110, 207 (1998)], and performing asymptotic or flux analysis. NQ is the preferred product channel, followed by XQ, R, and X. Moreover, the nonadiabatic quenching processes account for more than 80% of the total rate constants. WP snapshots show a reaction mechanism in good agreement with reaction probabilities. NQ, XQ, and R cross sections, and NQ rate constants decrease with the collision energy and j0, whereas the X reactivity increases, and XQ and R rates are nearly constant with j0. In general, quantum rate constants are smaller than experimental or quasiclassical data.

The kinetics and dynamics of the title reactions were studied using the quasiclassical trajectory (QCT) method and two ab initio analytical potential energy surfaces (PESs) developed by our group. In addition to the rate constant (T: 10-5000 K), we also considered a broad set of dynamic properties as a function of collision energy (up to 1.0 eV) and the rovibrational state of NO (v=0-2,j=1,8,12). The production of N(2)+O, reaction (1), dominates the reactivity of the N+NO system over the conditions studied, as expected from the large energy barriers associated to the NO+N exchange reaction, reaction (2). Moreover, the ground PES, which is barrierless for reaction (1), plays a dominant role. Most of the results were interpreted according to the properties of the PESs involved and the kinematics of the system. The QCT rate constants of reaction (1) are in agreement with the experimental data (T: 47-3500 K), including very recent low temperature measurements, and also with variational transition state kinetics and most of quantum dynamics calculations. In addition, the QCT average vibrational energy content of the N(2) product also agrees with the experimental and quantum data. The PESs used here could also be useful to determine equilibrium and nonequilibrium reaction rates at very high temperatures (e.g., 5000-15 000 K).

We present the Born–Oppenheimer, quantum dynamics of the reactions C(D1)+HD andC(D1)+n−D2 on the uncoupled potential energy surfaces a A1′ and b A1″, considering the Coriolis interactions and the nuclear-spin statistics. Using the real wavepacket method, we obtain initial-state-resolved probabilities, cross sections, isotopic branching ratios, and rate constants. Similarly to the C+n−H2 reaction, the probabilities present many a A1′ or few b A1″ sharp resonances, and the cross sections are very large at small collision energies and decrease at higher energies. At any initial condition, the C+HD reaction gives preferentially the CD+H products. Thermal cross sections, isotopic branching ratios, and rate constant k vary slightly with temperature and agree very well with the experimental values. At 300 K, we obtain for the various products k(CH+H)=(2.45±0.08)×10−10, k(CD+H)=(1.19±0.04)×10−10, k(CH+D)=(0.71±0.02)×10−10, k(CD+D)=(1.59±0.05)×10−10 cm3 s−1, and k(CD+H)/k(CH+D)=1.68±0.01. The b A1″ contributi...

We present the Born-Oppenheimer (BO) and Renner-Teller (RT) coupled-channel dynamics of the N((2)D) + HD --NH + D and N((2)D) + HD --ND + H reactions, considering the X (2)A(") and A (2)A(') states and RT and Coriolis couplings. We use the best available potential energy surfaces and obtain initial-state-resolved probabilities, cross sections, and rate constants via the real wave packet and flux methods for both electronic states. In contrast with the RT results of BO-X (2)A(") ones, we point out the role of RT and Coriolis interactions for both reactions and discuss the importance of the excited state on the initial-state-resolved dynamics and on the thermal kinetic rate. Moreover the competition for the formation of two products is discussed, showing some snapshots of the RT wave-packet density on the ground state. However, the BO approximation gives thermal rates that are smaller than those obtained via full RT calculation, especially at 300 K. Our calculated RT rate constants at room temperature are in good agreement with the experimental ones. The branching ratio is also calculated at T = 150-300 K at BO and RT levels. At 300 K the calculated value overestimates slightly the experimental data.

We present Renner-Teller (RT) and Born-Oppenheimer (BO) coupled-channel (CC) dynamics of the reaction (14)N((2)D)+(1)H(2)(X (1)Sigma(g) (+))--NH(X (3)Sigma(-))+H((2)S), considering both NH(2) coupled electronic states, X (2)B(1) and A (2)A(1), and Coriolis interactions. We use the best available potential energy surfaces (PESs), and we obtain initial-state-resolved reaction probabilities, cross sections, and rate constants through the real wavepacket and flux methods, taking into account the nuclear-spin statistics for both electronic states. Contrasting RT-CC with more approximate results, we point out the role of RT and Coriolis couplings, and discuss the importance of the A (2)A(1) excited state on the initial-state-resolved dynamics and on the thermal kinetic rate. Confirming the previous results, RT couplings transfer partly the reactivity from X (2)B(1) to A (2)A(1), and CC calculations are necessary to obtain accurate high-energy cross sections. When H(2) is initially rotating, RT couplings enhance strongly the electronic-state-resolved A (2)A(1) reactivity. Considering the nuclear-spin statistics for both electronic states, we find out that the A (2)A(1) state plays a significant role in the rotationally resolved dynamics of N((2)D)+ortho-H(2). However, the BO-X (2)B(1) approximation gives a thermal rate that is slightly smaller than the one obtained by the RT-CC calculations. This implies that this usual approximation is acceptable to calculate unresolved kinetic data of the title reaction. Our calculated rate constant values within the 213-300 K temperature interval are in excellent agreement with the experimental ones.

We present the Born–Oppenheimer dynamics of the depletion reaction NH(aΔ1)+H′→N(D2)+H2 and of the exchange one NH(aΔ1)+H′→NH′(aΔ1)+H, using the real wavepacket and flux methods and an accurate NH2(A A21) surface. We report coupled-channel reaction probabilities, cross sections, and rate constants, taking into account Coriolis couplings. Because the surface is barrierless and strongly bound, probabilities have small centrifugal thresholds and present sharp and large resonances, associated with long-lived collision complexes. Large J’s enhance the high-energy reactivity and favor the exchange reaction, owing to the negative Coriolis couplings, and to K that inhibits depletion but not exchange. Coriolis couplings are important in the collision complexes, and the centrifugal sudden approximation thus gives large errors. Cross sections are large at the threshold and minimal at intermediate collision energies and increase moderately at larger energies. Exchange is preferred, and both reactions are inhibited by...