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The quantum dynamics of three CH(X(2)Π) + D((2)S) reactions is studied by means of the coupled-channel time-dependent real-wavepacket (WP) and flux methods at collision energy Ecol ≤ 0.6 eV and on three potential energy surfaces (PESs): the Born-Oppenheimer (BO) ground PES X̃(3)A″ and the excited ones ã(1)A' and b̃(1)A″, coupled by nonadiabatic (NA) Renner-Teller (RT) effects. This three-state model is suitable for obtaining initial-state-resolved observables, is based on a complete analysis of the correlation diagram of the lowest electronic states of the CHD intermediate and of their NA interactions, and neglects the smaller coupling effects due to the asymptotic electronic angular momenta that become important in state-to-state dynamics. WPs are propagated on each PES at total angular momentum values J ≤ 70, with CH in the two lowest vibrational states v0 and in the ground rotational state j0 = 1. Reaction probabilities are obtained for three possible final products (f): (dP) CH decay and C((3)P) + HD(X(1)Σ(+)) formation that occurs on the uncoupled ground PES, (dD) CH decay and C((1)D) + HD(X(1)Σ(+)) formation that depends on the RT-coupled singlet species, and (ex) exchange to CD(X(2)Π) + H((2)S) available adiabatically from the X̃(3)A″ PES and nonadiabatically from ã(1)A' and b̃(1)A″. Observable cross sections σf,v0j0 and rate constants kf,v0j0 in the temperature range T = 100-2000 K are obtained for (dP), (dD), and (ex) channels. Comparing BO with RT probabilities, we show that NA effects are important at high J values for the (ex) channel at v0 = 1. Real time mechanisms on the three PESs show that RT couplings are opened after some time and clearly point out the formation of the product channels. Both cross sections and rate constants present the same sequence, for example σex,11σdP,01 ∼ σex,01σdP,11 ≫ σdD,11 ≫ σdD,01, and the CH vibrational excitation enhances the total removal CH+D reactivity by a factor of ∼1.7, mainly due to the increase of the (ex) channel contribution from ∼47% at v0 = 0 to ∼76% at v0 = 1. This fact implies a considerable vibrational enhancement of combustion processes at high temperature. In agreement with the probability results, the ã(1)A'/b̃(1)A″ RT coupling increases both σex,11 and kex,11 up to ∼30%. Moreover, including the three PESs in the dynamics simulation of CH+D increase by far the (ex)/(dP) branching ratio with respect to the CH + H' reaction. Thus, at room temperature, kdP,01 changes from 10.8 × 10(-11) to 3.4 × 10(-11) cm(3) s(-1) substituting H atom by D.

We present Born-Oppenheimer (BO) and Renner-Teller (RT) time dependent quantum dynamics studies of the reactions O(3P) + H2+(X2Σg+) → OH+(X3Σ-) + H(2S) and OH(X2Π) + H+. We consider the OH2+ X˜2A″ and Ã2A′ electronic states that correlate with a linear 2Π species. The electronic angular momenta operators L and L2 are considered in nonadiabatic coupled-channel calculations, where the associated RT effects are due to diagonal VRT potentials that add up to the PESs and to off-diagonal CRTcouplings between the potential energy surfaces (PESs). Initial-state-resolved reaction probabilities PI, integral cross sections σI, and rate constants kI are obtained using recent ab initio PESs and couplings and the real wavepacket formalism. Because the PESs are strongly attractive, PI have no threshold energy and are large, σI decrease with collision energy, and kI depend little on the temperature. The X˜2A″ PES is up to three times more reactive than the Ã2A′ PES and H2+ rotational effects (j0 = 0, 1) are negligible. The diagonal VRT potentials are strongly repulsive at the collinearity and nearly halve all low-energy observables with respect to the BO ones. The off-diagonal CRTcouplings are important at low partial waves, where they mix the X˜2A″ and Ã2A′ states up to ∼20%. However, VRT effects predominate over the CRT ones that change at most by ∼19% the BO values of σI and kI. The reaction O(3P) + H2+(X2Σg+) → OH+(X3Σ-) + H(2S) is probably one of the most reactive atom + diatom collisions because its RT rate constant at room temperature is equal to 2.26 × 10-10 cm3 s-1. Within the BO approximation, the present results agree rather well with recent quasiclassical and centrifugal-sudden data using the sa me PESs, This work was supported by the Spanish Ministry of Science and Innovation (MICINN projects CTQ2011-27857-C02-01 and CONSOLIDER INGENIO 2010 under grant no. CSD2009-00038 entitled ‘‘Molecular Astrophysics: the Herschel and Alma era’’). Thanks are also given to the ‘‘Generalitat de Catalunya’’ (Autonomous Government of Catalonia; refs. 2014SGR 25, 2014SGR 1582 and XRQTC) for some help. We gratefully acknowledge H. Guo and D. Xie for the matrix elements of the electronic angular momenta

Following previous studies on the O(

Following previous studies on the O(P-3) + H2(+)(X-2 Sigma(+)(g)) collisions, we present the nonadiabatic quantum dynamics of the reactions OH(X-2 Pi) + H'(+) -> OH'(X2P) + H+, exchange (e), -> OH+(X-3 Sigma(-)) + H'(S-2), quenching (q), and -> OH' + (X-3 Sigma(-)) + H(2S), exchange-quenching (eq). The reactants and products correlate via the ground X(2)A" and first excited A A(2)A' electronic states of OH2+, which are the degenerate components of linear (2)Pi species. Therefore, they are strongly perturbed by nonadiabatic Renner-Teller (RT) effects, opening the (q) and (eq) channels that are closed in the Born-Oppenheimer approximation. Using accurate potential energy surfaces (PESs) and RT matrix elements, initial-state-resolved reaction probabilities, real-time dynamics, cross sections, and rate constants of the product channels are obtained through the time-dependent real wavepacket (WP) method and full coupled-channel calculations. Owing to the nonadiabatic couplings, the WP jumps from the excited A A(2)A' surface to the A(2)A' ground PES, avoiding any barrier, opening the quenching channels, and giving many collision complexes into the deep minima of both PESs, as it is clearly shown by the oscillations of the reaction probabilities and by the time-dependent WP dynamics. All the results show that the nonadiabatic-RT channels (q) and (eq) are highly reactive, much more than the adiabatic one (e), pointing out large RT effects. The reactivity of the quenching channels is similar, accounting for 97% of the overall reactivity. In fact, the maximum values of the (q) and (eq) cross sections sigma(q) and sigma(eq) are equal to 31.6 A(2), whereas the maximum se value equals 1.34 A(2), and the maximum values of the rate constants k(q), k(eq), and k(e) are 2.07 Chi 10 Chi 10, 2.45 Chi 10 Chi 10, and 0.23 Chi 10 Chi 10 cm(3) s(-1). Some calculations show that the centrifugalsudden and the truncated coupled-channel approximations cannot be employed for the (q) channel. After a sharp increase at the threshold, sq and seq decrease at larger collision energies while se and the rate constants depend slightly on the collision energy and temperature, respectively. These findings are consistent with the barrierless nature of both PESs and the exoergicity of the quenching products, with the small role played by the centrifugal and RT barriers in the reactant channel, and with the large RT couplings in the OH2+ intermediates. Finally, we contrast the present results with those for the opposite reactions O + H-2 + and for the nonadiabatic-induced quenchings NH + H' and OH + H'.

We present the Born-Oppenheimer (BO) quantum mechanical (QM) dynamics of the CH decay (d) CH(X2Π) + H(2S) → C(3P) + H2(X1Σ(g)(+)) and of the H exchange reaction (e) CH(X2Π) + H′(2S) → CH′(X2Π) + H(2S) on the CH2 X̃3A″ adiabatic potential energy surface (PES) of Harding et al. (J. Phys. Chem. 1993, 97, 5472). A thorough analysis of the correlation diagram of the four lowest CH2 electronic states, as well as Renner-Teller and spin–orbit nonadiabatic test calculations on the X̃3A″, ã1A′, and b̃1A″ coupled PESs, validate the X̃3A″ BO results, confirming that these reactions occur essentially on the uncoupled X̃3A″ ground surface. We consider the CH molecule in the ground vibrational state and in the four lowest rotational states j0. Thus, we obtain initial-state resolved reaction probabilities, cross sections, and rate constants by propagating coupled-channel real wave packets and performing flux analyses. If J is the total angular momentum quantum number and K is its projection along the body-fixed z axis, CH + H gives essentially the C + H2 products via a barrierless K-inhibited insertion, CH2 resonances at low J, and large cross sections near the threshold. These cross sections decrease strongly with collision energy and depend slightly on j0. On the other hand, the small cross sections obtained for the (e) channel are nearly independent of energy. From initial-state resolved rate constants and Boltzmann populations at temperature T, we obtain QM thermal rate constants from 100 to 400 K: at 300 K, k(d) = (9.57 ± 0.96) × 10(-11) and k(e) = (1.41 ± 0.14) × 10(-11) cm(3) s(-1) for (d) and (e) reactions, respectively. The k(d) value is in good agreement with previous quasi-classical trajectory (QCT) results on the same PES, but it is larger than that observed at 297 K by a factor of 7. On the contrary, and in agreement with the small role of CH2 excited electronic states, X̃3A″ QCT and experimental rate constants agree at high temperatures. Thus, the discrepancy obtained at room T between theory and experiment should be due to an experimental error or to some theoretical effects that we have not been considered in this work. At the present state of the art, an experimental error is more likely and suggests a new measurement of the rate constant.

We present the quantum mechanical (QM) and quasiclassical trajectory (QCT) dynamics of the title reaction on two uncoupled surfaces, using a wavepacket (WP) method and considering some N 2 ( v , j ) vibrational and rotational states. The reaction is investigated by calculating initial-state-resolved reaction probabilities, cross sections, and rate constants, which are explained in terms of energy profiles and collision mechanisms. These properties reflect the large endo-thermicity of the reaction and the features of the surfaces. Indeed, at low v values we obtain large thresholds and the lower surface is more reactive than the higher one, whereas at high v the thresholds decrease or disappear and the upper surface becomes more reactive. QM and QCT results are in satisfactory agreement, except some differences at low or high collision energy and temperature. QCT rate coefficients agree also with some published results. WP snapshots and movies of QCT time evolution show clearly abstraction and insertion mechanisms depending on the initial conditions. Insertion proceeds via a reaction complex and we observe a QM Feshbach resonance for a specific initial condition. On the overall, the dynamical observables are consistent with the collision mechanisms.

We present both the Born–Oppenheimer (BO) and the nonadiabatic (NA) conical-intersection quantum dynamics of the title reactions, (1) and (2) , respectively. BO or NA calculations are carried out using adiabatic or diabatic electronic states, respectively, and we consider some vibrational ( v 0 ) and rotational ( j 0 ) states of O 2 , taking into account the Pauli principle. The results reflect the barrier or barrierless nature of reaction (1) or (2) , respectively, and the former is, thus, much less reactive than the latter. Reaction (1) is direct and its probabilities and cross sections increase with the collision energy from a threshold value, are slightly affected by NA couplings only at high energies, increase with v 0 , and are essentially unchanged by j 0 . On the contrary, reaction (2) is indirect and its probabilities and cross sections decrease with the collision energy without any threshold, are significantly lowered by NA couplings at low energies, and decrease with both v 0 and j 0 .

We have investigated the dynamics of the title reaction with the Gray and Balint-Kurti approach, which propagates real wave packets (WP) under an arccos mapping of a scaled and shifted Hamiltonian. We have considered H 2 rotational quanta j=0 and 1 and obtained reaction probabilities using reactant coordinates and the flux analysis. We have calculated accurate reaction probabilities for total angular momentum quantum number J=0, centrifugal-sudden probabilities for J>0, cross sections, and the room temperature rate constant. The present cross sections are in good agreement with previous quasiclassical trajectory (QCT) results and the theoretical rate constant compares rather well with that observed. WP snapshots show that the reaction occurs via a C2v insertion mechanism, confirming previous QCT calculations.

The quantum dynamics of the reaction D{sub 2} + OH {yields} DOH + D on the Wu-Schatz-Lendvay-Fang-Harding ab initio-based potential energy function is investigated. A recently developed four-atom implementation of the real wave packet method is employed. Extensive six-dimensional calculations for a total angular momentum of J = 0 and, within the helicity-decoupled approximation, numerous J > 0 calculations are performed. Cross sections and rate constants for reaction are estimated using a J-shifting procedure and compared with quasi-classical trajectory, transition state theory, and experimental results. The results are also contrasted with comparable results for H{sub 2} + OH. A surprising feature is that our rate constants agree best with zero-curvature transition state theory results, indicating that tunneling may not be as important as expected.

We present the adiabatic quantum dynamics of the proton-transfer reaction H((2)S) + HeH(+)(X(1)Σ(+)) → H2(+)(X(2)Σg(+)) + He((1)S) on the HeH2(+) X̃(2)Σ(+) RMRCI6 (M = 6) PES of C. N. Ramachandran et al. ( Chem. Phys. Lett. 2009, 469, 26). We consider the HeH(+) molecule in the ground vibrational–rotational state and obtain initial-state-resolved reaction probabilities and the ground-state cross section σ0 and rate constant k0 by propagating time-dependent, coupled-channel, real wavepackets (RWPs) and performing a flux analysis. Three different wavepackets are propagated to describe the wide range of energies explored, from cold (0.0001 meV) to hyperthermal (1000 meV) collision energies, and in a temperature range from 0.01 to 2000 K. We compare our time-dependent results with the time-independent ones by D. De Fazio and S. Bovino et al., where De Fazio carried out benchmark coupled-channel calculations whereas Bovino et al. employed the negative imaginary potential and the centrifugal-sudden approximations. The RWP cross section is in good agreement with that by De Fazio, except at the lowest collision energies below ∼0.01 meV, where the former is larger than the latter. However, neither the RWP and De Fazio results possess the huge resonance in probability and cross section at 0.01 meV, found by Bovino et al., who also obtained a too low σ0 at high energies. Therefore, the RWP and De Fazio rate constants compare quite well, whereas that by Bovino et al. is in general lower.

We report three-dimensional quantum calculations of total angular momentum J=0 reaction probabilities, J-shifting cross sections, and rate constants of the title reaction. Employing the real wave packet approach, we propagate wave packets corresponding to several O2(v,j) initial levels on the X 2A′ potential surface of Sayos et al. As collision energy increases, the average probabilities first increase monotonically and then become nearly constant, while the cross sections rise in the overall energy range. Numerous probability resonances point out the formation of NOO collision complexes and NO final states. Rotational excitation in O2 decreases the collisional energy thresholds and enhances the state-resolved rate constants, mainly at low temperature. O2 vibrational excitation inhibits the reactivity, although the energy thresholds are still reduced. With respect to previous quasiclassical and mixed quantum-classical studies, we obtain lower thresholds and cross sections but similar rate constants, which...

We present the spin-orbit (SO) and Renner-Teller (RT) quantum dynamics of the spin-forbidden quenching O((1)D) + N(2)(X(1)Σ(g)(+)) → O((3)P) + N(2)(X(1)Σ(g)(+)) on the N(2)O X(1)A', ã(3)A", and b(3)A' coupled PESs. We use the permutation-inversion symmetry, propagate coupled-channel (CC) real wavepackets, and compute initial-state-resolved probabilities and cross sections σ(j(0)) for the ground vibrational and the first two rotational states of N(2), j(0) = 0 and 1. Labeling symmetry angular states by j and K, we report selection rules for j and for the minimum K value associated with any electronic state, showing that ã(3)A" is uncoupled in the centrifugal-sudden (CS) approximation at j(0) = 0. The dynamics is resonance-dominated, the probabilities are larger at low K, σ(j(0)) decrease with the collision energy and increase with j(0), and the CS σ(0) is lower than the CC one. The nonadiabatic interactions play different roles on the quenching dynamics, because the X(1)A'-b(3)A' SO effects are those most important while the ã(3)A"-b(3)A' RT ones are negligible.

We present the quantum mechanical (QM) and quasiclassical trajectory (QCT) dynamics of the title reac- tion on two uncoupled surfaces, using a wavepacket (WP) method and considering some N2(v, j) vibra- tional and rotational states. The reaction is investigated by calculating initial-state-resolved reaction probabilities, cross sections, and rate constants, which are explained in terms of energy profiles and col- lision mechanisms. These properties reflect the large endo-thermicity of the reaction and the features of the surfaces. Indeed, at low v values we obtain large thresholds and the lower surface is more reactive than the higher one, whereas at high v the thresholds decrease or disappear and the upper surface becomes more reactive. QM and QCT results are in satisfactory agreement, except some differences at low or high collision energy and temperature. QCT rate coefficients agree also with some published results. WP snapshots and movies of QCT time evolution show clearly abstraction and insertion mecha- nisms depending on the initial conditions. Insertion proceeds via a reaction complex and we observe a QM Feshbach resonance for a specific initial condition. On the overall, the dynamical observables are con- sistent with the collision mechanisms.

The Renner-Teller (RT) coupled-channel dynamics for the C((1)D)+H(2)(X(1)Σ(g) (+))→CH(X(2)Π)+H((2)S) reaction has been investigated for the first time, considering the first two singlet states ã̃(1)A' and b(1)A'' of CH(2) dissociating into the products and RT couplings, evaluated through the ab initio matrix elements of the electronic angular momentum. We have obtained initial-state-resolved probabilities, cross sections and thermal rate constants via the real wavepacket method for both coupled electronic states. In contrast to the N((2)D)+H(2)(X(1)Σ(g)(+)) system, RT effects tend to reduce probabilities, cross sections, and rate constants in the low energy range compared to Born-Oppenheimer (BO) ones, due to the presence of a repulsive RT barrier in the effective potentials and to long-lived resonances. Furthermore, contrary to BO results, the rate constants have a positive temperature dependence in the 100-400 K range. The two-state RT rate constant at 300 K, lower than the BO one, remains inside the error bars of the experimental value.

The Ne + H(2)(+)(v(0) = 0-4, j(0) = 1) proton transfer reaction has been studied in a wide collision energy (E(col)) interval, using the time dependent real wave packet method and taking into account the Coriolis coupling (CC-RWP method) and employing a recent ab initio potential energy surface, widely extending the reaction conditions previously explored at the CC level. The reaction probability shows a strong oscillatory behavior vs E(col) and the presence of sharp resonances, arising from metastable NeH(2)(+) states. The behavior of the reaction cross section σ vs E(col) depends on the vibrational level and can in general be interpreted in terms of the late barrier character of the potential energy surface and the existence (or not) of threshold energy. The situation is particularly complex for v(0) = 2, as σ(v0=2, j0=1) presents significant oscillations with E(col) up to ≈0.33 eV, which probably reflect the resonances found in the reaction probability. Hence, it would be particularly interesting to investigate the Ne + H(2)(+)(v(0) = 2, j(0) = 1) reaction experimentally, as some resonances survive the partial wave summation. The state selected cross sections compare well with previous CC quantum and experimental results, and although the previous centrifugal sudden RWP cross sections are reasonable, the inclusion of the Coriolis coupling is important to achieve a quantitative description of this and similar systems.

A quantum dynamics study for the NH(a(1)Δ) + D((2)S) reactions using coupled channel time dependent real wavepacket formalism is presented. Moreover, the Renner-Teller (RT) interactions between two electronic states of NHD (X[combining tilde](2)A'' and Ã(2)A') have been taken into account by means of semiempirical RT matrix elements. The introduction of RT effects opens the possibility of studying not only the adiabatic reactions [depletion (d) to N((2)D) + HD(X(1)Σ(+)) and exchange (e) to ND(a(1)Δ) + H((2)S)] but also nonadiabatic ones [quenching (q) to NH(X(3)Σ(-)) + D((2)S) and exchange-quenching (eq) to ND(X(3)Σ(-)) + H((2)S)]. Reaction probabilities, cross sections, isotopic effects, and rate constants are presented for all the before mentioned reactions. RT results are compared with Born-Oppenheimer, quasiclassical, and experimental data. Contrasting with previous NH + H results, we point out interesting RT and isotopic effects, which depend on the D and H masses and on the tunneling of the H atom. In fact, RT effects, near-threshold cross sections, and rate constants are smaller in NH + D than in NH + H, as expected from the masses of the attacking atoms. Our rate constants and quenching branching ratio agree well with previous quasiclassical and experimental data, validating the semiempirical RT coupling we employ. Some small differences between calculated and measured rate constants might be due to the theoretical approximations and to the large experimental error bars.

We present the Born-Oppenheimer, quantum dynamics of the reactions C((1)D)+HD and C((1)D)+n-D(2) on the uncoupled potential energy surfaces ã (1)A' and b (1)A", 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-H(2) reaction, the probabilities present many ã (1)A' or few b (1)A" 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) x 10(-10), k(CD+H)=(1.19+/-0.04) x 10(-10), k(CH+D)=(0.71+/-0.02) x 10(-10), k(CD+D)=(1.59+/-0.05) x 10(-10) cm(3) s(-1), and k(CD+H)/k(CH+D)=1.68+/-0.01. The b (1)A" contribution to cross sections and rate constants is always large, up to a maximum value of 62% for a rotationally resolved C+D(2) rate constant. The upper b (1)A" state is thus quite important in the C((1)D) collision with H(2) and its deuterated isotopes, as the agreement between theory and experiment shows.

We present the Born-Oppenheimer coupled-channel dynamics of the reaction (12)C((1)D)+(1)H(2)(X (1)Sigma(g) (+))--CH(X (2)Pi)+H((2)S), considering the uncoupled CH(2) states ã (1)A(1) and b (1)B(1), the permutation-inversion symmetry, and Coriolis interactions. Using accurate MRCI potential energy surfaces (PESs), we obtain initial-state-resolved reaction probabilities, cross sections, and rate constants through the time-dependent, real wavepacket (WP) and flux methods, taking into account the proton-spin statistics for both electronic species. Comparing results on both PESs, we point out the role of the b (1)B(1) upper state on the initial-state-resolved dynamics and on the thermal kinetic rate. WP probabilities at J=0 and cross sections at E(col)=0.080 eV agree quite well with quantum-mechanical time-independent findings. Probabilities and WP snapshots show the different reaction mechanisms on the PESs, i.e., an ã (1)A(1) indirect perpendicular insertion and a b (1)B(1) direct sideways collision, associated with many and few sharp resonances, respectively. All cross sections are very large at low E(col), decrease at high energies, and that of the lowest reactant state presents some weak resonances. As the temperature increases from 100 to 400 K, the ã (1)A(1) rate constant increases slightly from 1.37x10(-10) to 1.43x10(-10) cm(3) s(-1), whereas the b (1)B(1) one decreases from 1.30x10(-10) to 0.98x10(-10) cm(3) s(-1). In this temperature range, the b (1)B(1) contribution to the total rate constant thus decreases from 49% to 41%. At 300 K, the WP and experimental rates are equal to (2.45+/-0.08)x10(-10) and (2.0+/-0.6)x10(-10) cm(3) s(-1), respectively.

We present a quantum study of the reaction F((2)P) + HCl(X(1)Sigma(+)) --> HF(X(1)Sigma(+)) + Cl((2)P) on a recently computed 1(2)A' ground-state surface, considering HCl in the ground vibrational state, with up to 16 rotational quanta j(0). We employ the real wavepacket (WP) and flux methods for calculating coupled-channel (CC) and centrifugal-sudden (CS) initial-state probabilities up to J = 80 and 140, respectively. We also report CC and CS ground-state cross sections and CS excited-state cross sections and discuss the dynamics analyzing WP time evolutions. The HCl rotation highly enhances reaction probabilities and cross sections, as it was previously found for probabilities at J

We present the Born-Oppenheimer dynamics of the depletion reaction NH(a(1)Delta)+H(')--N((2)D)+H(2) and of the exchange one NH(a(1)Delta)+H(')--NH(')(a(1)Delta)+H, using the real wavepacket and flux methods and an accurate NH(2)(A (2)A(1)) 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 the NH rotational excitation. Finally, the present rate constants are in good agreement with previous experimental and semiclassical results.

We present Coriolis coupling effects on the initial-state-resolved dynamics of the insertion reaction N((2)D)+H(2)(X (1)Sigma(g) (+))-->NH(X (3)Sigma(-) and a (1)Delta)+H((2)S), without and with nonadiabatic Renner-Teller (RT) interactions between the NH(2) X (2)B(1) and A (2)A(1) electronic states. We report coupled-channel (CC) Hamiltonian matrix elements, which take into account both Coriolis and RT couplings, use the real wave-packet and flux methods for calculating initial-state-resolved reaction probabilities, and contrast CC with centrifugal-sudden (CS) results. Without RT interactions, Coriolis effects are rather small up to J=40, and the CS approximation can be safely employed for calculating initial-state-resolved, integral cross sections. On the other hand, RT effects are associated with rather large Coriolis couplings, mainly near the linearity of NH(2), and the accuracy of the CS approximation thus breaks down at high collision energies, when the reaction starts on the excited A (2)A(1) surface. We also present the CC-RT distribution of the X (3)Sigma(-) and a (1)Delta electronic states of the NH products.

A quantum-mechanical (QM) and quasiclassical trajectory (QCT) study was performed on the title reaction, using a pseudotriatomic ab initio based surface. Probabilities and integral cross sections present some clear peaks versus the collision energy E(col), which we assign to Feshbach resonances of the transition state, where the light H atom oscillates between the heavy Cl and CH(3) groups. For ground-state reactants, reactivity is essentially of quantum origin (QCT observables and oscillations are smaller, or much smaller, than QM ones), and the calculated integral cross section and product distributions are in reasonable agreement with the experiment. The reaction occurs through an abstraction mechanism, following both a direct and an indirect mechanism. The quasiclassical trajectory calculations show the participation of a short-lived collision complex in the microscopic reaction mechanism. Finally, QCT differential cross sections of Cl+CH(4)-->HCl (nu(')=0 and 1)+CH(3) oscillate versus E(col), whereas experimentally this only occurs for HCl (nu(')=1). This theoretical result and other oscillating properties found here could, however, be related to the existence of a Feshbach resonance for the production of HCl (nu(')=1), as suggested by experimentalists.

We present the Born-Oppenheimer (BO) and Renner-Teller (RT) quantum dynamics of the reaction (14)N((2)D)+(1)H(2)(X (1)Sigma(g) (+))--NH(X (3)Sigma(-))+H((2)S), considering the NH(2) electronic states X (2)B(1) and A (2)A(1). These states correlate to the same (2)Pi(u) linear species, are coupled by RT nonadiabatic effects, and give NH(X (3)Sigma(-))+H and NH(a (1)Delta)+H, respectively. We develop the Hamiltonian matrix elements in the R embedding of the Jacobi coordinates and in the adiabatic electronic representation, using the permutation-inversion symmetry, and taking into account the nuclear-spin statistics. Collision observables are calculated via the real wave-packet (WP) and flux methods, using the potential-energy surfaces of Santoro et al. [J. Phys. Chem. A 106, 8276 (2002)]. WP snapshots show that the reaction proceeds via an insertion mechanism, and that the RT-WP avoids the A (2)A(1) potential barrier, jumping from the excited to the ground surface and giving mainly the NH(X (3)Sigma(-)) products. X (2)B(1) BO probabilities and cross sections show large tunnel effects and are approximately four to ten times larger than the A (2)A(1) ones. This implies a BO rate-constant ratio k(X (2)B(1))k(A (2)A(1)) approximately 10(5) at 300 K, i.e., a negligible BO formation of NH(a (1)Delta). When H(2) is rotationally excited, RT couplings reduce slightly the X (2)B(1) reaction observables, but enhance strongly the A (2)A(1) reactivity. These couplings are important at all collision energies, reduce the collision threshold, and increase remarkably reaction probabilities and cross sections. The RT k(A (2)A(1)) is thus approximately 3.3 order of magnitude larger than the BO value, and degeneracy-averaged, initial-state-resolved rate constants increase by approximately 13% and by approximately 47% at 300 and 500 K, respectively. Owing to an overestimation of the X (2)B(1) potential barrier, the calculated thermal rate is too low with respect to that observed, but we obtain a good agreement by shifting down the calculated cross section.

We present a quantum-mechanical investigation of the LiH depletion reaction LiH+H--Li+H2 and of the H exchange reaction LiH+H'--LiH'+H. We report product distributions, rate constant, and mechanism of the former, and rate constant and mechanism of the latter reaction. We use the potential-energy surface by Dunne et al. [Chem. Phys. Lett. 336, 1 (2001)], the real-wave-packet method by Gray and Balint-Kurti [J. Chem. Phys. 108, 950 (1998)], and the J-shifting approximation. The 1H2 nuclear-spin statistics and progressions of vib-rotational states (v',j') rule both initial-state-resolved and thermal product distributions, which have saw-toothed shapes with odd j' preferred with respect to even j'. At high collision energies and temperatures, we obtain a regular 3-to-1 intensity alternation of rotational states. At low collision energies and temperatures, the degeneracy and density of many H2 levels can, however, give more irregular distributions. During the collision, the energy flows from the reactant translational mode to the product vibration and recoil ones. The rate constants of both reactions are not Arrhenius type because the reactions are barrier-less. The low-temperature, LiH depletion rate constant is larger than the H exchange one, whereas the contrary holds at high temperature. The real-time mechanisms show the nuclear rearrangements of the nonreactive channel and of the reactive ones, and point out that the LiH depletion is preferred over the H exchange at short times. This confirms the rate-constant results.

We report real wave packet (WP) calculations of reaction probabilities, cross sections, rate constants, and product distributions of the reaction N(4S) + O2(X3 ) → NO(X2Π) + O(3P). We propagate initial WPs corresponding to several O2 levels, and employ reactant coordinates and a flux method for calculating initial-state-resolved observables, or product coordinates and an asymptotic analysis for calculating state-to-state quantities. Exact or J-shifting calculations are carried out at total angular momentum J=0 or J>0, respectively. We employ the recent X 2A' S3 potential energy surface (PES) by Sayós et al. and the earlier a 4A' PES by Duff et al. In comparing S3 results with the WP ones of a previous X 2A' S2 PES, we find lower S3 energy thresholds and larger S3 probabilities, despite the higher S3 barrier. This finding is due to the different features of the doublet PESs in the reactant and product channels, at the transition state, and in the NO2 equilibrium region. We analyze the effects of the O2 initial level and discuss Cs abstraction or insertion mechanisms. Tunnel effects through the S3 barrier enhance the room-temperature rate constant by ~ 3.7 times with respect to the previous S2 WP rate, thus improving the agreement with the experimental result. The NO vibrational distribution is inverted and the rotational ones are strongly oscillating. We explain these non-statistical results showing that the reaction partners approach each other with a large impact parameter. The WP vibrational distribution is however different from that observed, which is oscillating. WP calculations show that the new S3 PES describes accurately several features of the X 2A' state, although a lowering of its barrier height by ~ 0.56 kcal/mol should bring calculated and observed rate constants in full agreement.

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.

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...