Benchmark ab Initio Characterization of the Complex Potential Energy Surfaces of the X - + NH 2 Y [X, Y = F, Cl, Br, I] Reactions

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 122; no. 7; pp. 1886 - 1895
• Main Authors: Hajdu, Bálint, Czakó, Gábor
• Format: Journal Article
• Language: English
• Published: United States 22-02-2018
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.7b11927

We report a comprehensive high-level explicitly correlated ab initio study on the X
+ NH
Y [X,Y = F, Cl, Br, I] reactions characterizing the stationary points of the S
2 (Y
+ NH
X) and proton-transfer (HX + NHY
) pathways as well as the reaction enthalpies of various endothermic additional product channels such as H
+ NHXY, XY
+ NH
, XY + NH
, and XHY
+ NH. Benchmark structures and harmonic vibrational frequencies are obtained at the CCSD(T)-F12b/aug-cc-pVTZ(-PP) level of theory, followed by CCSD(T)-F12b/aug-cc-pVnZ(-PP) [n = Q and 5] and core correlation energy computations. In the entrance and exit channels we find two equivalent hydrogen-bonded C
minima, X
···HH'NY and X
···H'HNY connected by a C
first-order saddle point, X
···H
NY, as well as a halogen-bonded front-side complex, X
···YNH
. S
2 reactions can proceed via back-side attack Walden inversion and front-side attack retention pathways characterized by first-order saddle points, submerged [X-NH
-Y]
and high-energy [H
NXY]
, respectively. Product-like stationary points below the HX + NHY
asymptotes are involved in the proton-transfer processes.