ISSN:
0020-7608
Keywords:
Computational Chemistry and Molecular Modeling
;
Atomic, Molecular and Optical Physics
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Hydrogen addition to acetylene has been studied by molecular orbital methods with the unrestricted Hartree-Fock (HF)approach and with Møller-Plesset (MP) perturbation theory up to fourth order using the 6-31G*, 6-31G**, and 6-311G** basis sets. For each basis set a number of points along an approximate reaction path were calculated by fixing the attacking H—C distance and optimizing all of the remaining parameters. At these geometries, single point MP4 calculations with and without spin projection were carried out, yielding the position, height, and shape of the addition barrier at the various levels of calculation with each of the three basis sets. The results of this approach were confirmed by a grid search of the region near the transition state using the 6-31G* basis set. The unprojected MP2, MP3, and MP4 barriers are too narrow and are 10-20 kcal/mol too high. With spin projection, the barriers are much lower and broader. At the PMP4SDTQ/6-311G** level, with zero point energy calculated at UHF/6-31G*, the vibrationally adiabatic barrier at 0 K is 4.0 kcal/mol, and the attacking H—C distance is 2.0 Å.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/qua.560320729
