Adiabatic Capture Theory Applied to N + NH → N2 + H at Low Temperature

Accurate Potential Energy Surface for Quartet State HN2 and Interplay of N(4S) + NH(X̃3Σ-) versus H + N2(A3Σu+) Reactions

A global potential energy surface for the lowest quartet state of HN₂ is reported for the first time from accurate multireference ab initio calculations extrapolated to the complete basis set limit using the double many-body expansion method. All its stationary points are characterized, with the lowest quartet of HN₂ predicted to have a bent global minimum 36 kcal mol^-1 below the N(⁴S) + NH(X̃³Σ^-) asymptote, from which it is barrierlessly achievable. The entire set of calculated ab initio points has been fitted for energies up to 1000 kcal mol^-1 above the global minimum with an RMSD of 0.89 kcal mol^-1, a gap comprising all identified stationary points. Special care is taken in modeling the involved long-range forces and cusps caused by crossing seams. The novel PES prompts for the calculation of rate constants for several unexplored reactions that are relevant for combustion, plasma, and atmospheric chemistry.

QUASI-CLASSICAL TRAJECTORY STUDY OF THE REACTION N + NH (v = 0–3, j=0) → N2 + H

The quasi-classical trajectory (QCT) calculations have been carried out for the reaction N + NH (v = 0–3, j=0) → N2 + H on the ground state of double many-body expansion (DMBE) potential energy surface [Caridade, PJSB, Poveda LA, Rodrigues SPJ, Varandas AJC, J Phys Chem A111:1172, 2007]. The influence of reagent vibrational excitation on reaction probability for total angular momentum J = 0 and integral cross section (ICS) at collision energies ranging from 0.1 eV to 1.0 eV has been investigated. The reaction probability tends to decrease with increasing collision energy and increase with the rising of initial vibration state, although some fluctuations appear. The ICS declines monotonously with the increase of collision energy and v. The product rotational alignment factor 〈P2(j′•k)〉 has also been calculated, and its value has a declining trend with the increase of collision energy. In spite of that, the results still show that the product is highly aligned. In addition, the vibrational excitation effect on the product polarization has also been studied. All the distributions of P(ϕr), P(θr), and the generalized polarization dependent differential cross sections indicate dependent behaviors on v.

STEREODYNAMICS AND ISOTOPE EFFECTS FOR THE REACTION N + NH → N2 + H

Quasi-Classical Trajectory (QCT) calculations have been carried out to study the stereodynamics of the reactions N + NH → N 2 + H and isotopic effects on the product polarization at collision energies of 10.0 kcal/mol and 25.0 kcal/mol which proceed on the Double-Many-Body-Expansion (DMBE) potential energy surface. The distribution of dihedral angle P(ϕr), and the distribution of angle between k and j′, P(θr) are discussed in detail. Furthermore, four generalized polarization dependent differential cross sections (PDDCSs) (2π/σ)(dσ00/dω), (2π/σ)(dσ20/dω), (2π/;σ)(dσ22+/dω), and (2π/σ)(dσ21 -∕dω) are presented. The results reveal that isotope effect plays an important role for P(ϕr) and P(θr) distribution, and the PDDCSs exhibit similar collision energy dependency relationship at low and high collision energies.

DIABATIC ELECTRONIC MANIFOLD OF HN2(2A′) AND N + NH REACTION DYNAMICS ON ITS LOWEST ADIABAT

A previously reported approach [J. Chem. Phys.97:867, (1997)] to back transform the diagonal adiabats into a 2 × 2 diabatic potential matrix has been utilized to generate a global multi-sheeted form for the title system. Global adiabatic dynamics calculations carried out on the new form using the quasi-classical trajectory method yield results that lie essentially within the statistical error of similar calculations performed on the best surface reported thus far for the title reaction. This makes it suitable for future adiabatic and nonadiabatic calculations carried out either using classical or quantum methods.

Cold N+NH collisions in a magnetic trap

We present an experimental and theoretical study of atom-molecule collisions in a mixture of cold, trapped N atoms and NH molecules at a temperature of ∼600  mK. We measure a small N+NH trap loss rate coefficient of k(loss)(N+NH)=9(5)(3)×10(-13)  cm(3) s(-1). Accurate quantum scattering calculations based on ab initio interaction potentials are in agreement with experiment and indicate the magnetic dipole interaction to be the dominant loss mechanism. Our theory further indicates the ratio of N+NH elastic-to-inelastic collisions remains large (>100) into the mK regime.

Nonadiabatic quantum dynamics calculations for the N + NH --> N(2) + H reaction

Nonadiabatic quantum dynamics calculations on the two coupled potential energy surfaces (PESs) (1(2)A' and 2(2)A') and also adiabatic quantum calculations on the lowest adiabatic PES are reported for the title reaction. Reaction probabilities for total angular momenta, J, varying from 0 to 160, are calculated to obtain the integral cross section (ICS) for collision energies ranging from 0.05 to 1.0 eV. Calculations using both the close coupling and the Centrifugal Sudden (CS) approximation are carried out to evaluate the role of Coriolis coupling effects for this reaction. The results of the nonadiabatic calculations show that the nonadiabatic effects in the title reaction for the initial state of NH (v = 0, j = 0) could be neglected, at least in the collision energy range considered in this study.