A new global potential energy surface is reported for the (4)A'' ground electronic state of the N(3) system from double many-body expansion theory and an extensive set of accurate ab initio energies extrapolated to the complete basis set limit. It shows three equivalent metastable potential wells for C(2v) geometries that are separated from the three N((4)S) + N(2) asymptotes by energy barriers as predicted from previous ab initio work. The potential well and barrier height now predicted lie 42.9 and 45.9 kcal mol(-1) above the atom-diatom dissociation limit, respectively, being about 1 kcal mol(-1) lower than previous theoretical estimates. The ab initio calculations here reported predict also a (4)B(1)/(4)A(2) conical intersection and reveal a new minimum with D(3h) symmetry that lies 147 kcal mol(-1) above the atom-diatom asymptote. All major topographical features of the potential energy surface are accurately described by the DMBE function, including the weakly bound van der Waals minima at large atom-diatom separations.
We report a global accurate double-sheeted potential energy surface for the lowest doublet states with (2)A″ symmetry of the N(3) radical using the double many-body expansion method. The functional form ensures by construction the degeneracy of the two adiabatic sheets along the D(3h) line and the corresponding cusp behavior. Calibrated from multireference configuration interaction energies, it reproduces all the predicted stationary structures on both sheets and ensures a correct description of the dissociation limits. A test quasiclassical trajectory study of N((2)D) + N(2) collisions is also reported in the lowest adiabatic sheet of the potential energy surface. The results commend it for both classical and quantum dynamics studies, while serving as a building block for the potential energy surfaces of larger nitrogen allotropes and azides.
Quasiclassical trajectories have been integrated to study the exchange reaction of molecular nitrogen in collisions with atomic nitrogen for temperatures over the range of 1273 < or = T (K) < or = 10,000. A recently proposed potential energy surface for the ground A'' quartet state of the system has been employed. If compared to previous theoretical studies, the results of the present work show a higher reactivity due to a lower barrier, with a study of the effect of this height in the thermal rate constant being also performed. Vibrational energy transfer via chemical reaction and/or inelastic collisions are also studied.
Rate constants for the electronic quenching reaction N( 2 D) + N 2 → N( 4 S) + N 2 are calculated for temperatures over the range of 240 ≤ T/K ≤ 1000 using an accurate set of three global electronic potential energy surfaces for the N 3 system ( 4 A″, 2 A′, and 2 A″). The nuclear motion is treated by running quasiclassical trajectories, incorporating spin-forbidden transitions with the trajectory surface hopping method. The exclusively theoretical results are compared with available experimental data for the reaction and contribute to clarify the discrepancies among them. The rate constants at higher temperatures achieved in the atmosphere, for which no experiments have been performed, are presented for the first time. The impact of the results in atmospheric modeling is analyzed, predicting at what altitudes this reaction will play an important role.
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