Ab Initio Evaluation of the Barrier Height.Theoretical Rate Constant of the NH3 + H .fwdarw. NH2 + H2 Reaction

Abstract

The rate constant of the NH3 + H -NH2 + H2 reaction was calculated using the nonvariational transition-state theory for the temperature range 500-2000 K. The quality of the theoretical barrier height depends on the amount of correlation energy taken into account, on the post-MP4 corrections, and on the spin decontamination when radicals are involved. The quadratic configuration interaction (QCI) method gives values higher than the perturbational post-MP4 SAC4/A1 method. The basis set superposition error and the sources of thermal corrections (theoretical or experimental) have minor importance. We found that the two rate constants using the SAC4/A1 and QCI barriers represent an upper and lower bound, respectively, to the available experimental values.

Dual-Level Reaction-Path Dynamics (the /// Approach to VTST with Semiclassical Tunneling). Application to OH + NH3 .fwdarw. H2O + NH2

“…For the high-level data, we used the energetics obtained at the QCIT//PTZ+ level and the optimized geometries obtained at the PTZ-P level, and the vibrational frequencies were calculated at the PDZ-F level. We obtained the low-level surface data with two different approaches, namely, the semiempirical SRP approach described in section 2 and the ab initio PDZ level presented in ref 19. Thus, the two dynamics levels considered here may be denoted QCIT//PTZ+[PDZ4-]///SRP and QCIT//PTZ+[PDZ+]///PDZ, respectively.…”

Global dynamics and transition state theories: Comparative study of reaction rate constants for gas‐phase chemical reactions

“…120,[130][131][132][133][134] Among them, the construction of the global Corchado-Espinosa (CE) PES 120 paves the way of the dynamical 120 and QD 133,134 are compared in Figure 9. The rate constants calculated from QD 133 are lower than those of the VTST over the considered temperature range.…”

Insights Gained by Modeling the Kinetics of Archetypal Hydrogen Atom Transfer Reactions: NH3 + ·H ⇆ H2N· + H2 and CH4 + ·H ⇆ H3C· + H2

“…There has been a multiyear effort by Espinosa‐García et al and Corchado to obtain an accurate PES for reaction (1) . The latest of these efforts produced a highly parameterized PES obtained with high‐level ab initio calculations at the CCSD(T)/cc‐pVTZ level .…”