Protonated acetylene revisited |
| |
Authors: | Brian T Psciuk Victor A Benderskii H Bernhard Schlegel |
| |
Institution: | (1) Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA;(2) Institute of Problems of Chemical Physics, RAS, 142432 Moscow Region, Chernogolovka, Russia |
| |
Abstract: | The potential energy surface for protonated acetylene has been re-examined with large basis sets and highly correlated methods.
The energy difference of 3.6–3.8 kcal/mol between the classical structure and non-classical (bridged) structure computed with
CCSD (T)/cc-pVQZ, CCSD(T)/6-311+G(3df,2pd), BD(T)/cc- pVQZ, BD(T)/6-311+G(3df,2pd) and CBS-APNO methods is in very good agreement
with the best previous calculations, 3.7–4.0 kcal/mol. In contrast, BLYP, B3LYP, PW91, PBE and TPSS density functional methods
do rather poorly, yielding −0.52. 0.29, 1.81, 2.16 and 0.62 kcal/mol, respectively, with the 6-311+G(3df,2pd) basis. MP2 calculations
predict the classical structure to be a transition state; however, frequency calculations at the CCSD/6-311+G(3df,2pd) level
of theory show that the classical structure is a local minimum. CCSD(T), BD(T) and CBS-APNO energy calculations along the
MP2/6-311+G(3df,2pd) reaction path indicate that the classical structure is a shallow local minimum separated from the non-classical
structure by a very small barrier of 0.11–0.13 kcal/mol. Because the barrier for proton exchange between the non-classical
isomers via the classical structure is broad and nearly flat at the top, the tunneling splitting should be reduced, possibly
accounting for the 15% difference between the calculated and experimental barrier heights.
Contribution to the Fernando Bernardi Memorial Issue. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|