The unimolecular dissociation of H{sub 2}CO on the lowest triplet potential-energy surface
- Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia30602 (United States)
The unimolecular dissociation reaction of H{sub 2}CO on the triplet potential-energy surface has been studied via {ital ab initio} electronic structure theory. The stationary point geometries for the equilibrium and transition state are determined employing the configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with large basis sets up to the correlation consistent (cc)-pVQZ basis. With the best method, cc-pVQZ CCSD(T), the first excited triplet ({tilde a}{sup 3}A{sup {double_prime}}) state lies 72.2kcal/mol (25260cm{sup {minus}1}) above the ground ({tilde X}{sup 1}A{sub 1}) state of H{sub 2}CO, which is in excellent agreement with the experimental observation of 72.03kcal/mol (25194cm{sup {minus}1}). The dissociation limit (H{center_dot}+HCO{center_dot}) is located at 86.3kcal/mol (30170cm{sup {minus}1}) above the ground state of H{sub 2}CO, which is again in good agreement with the two experimentally determined values of 86.57kcal/mol (30280cm{sup {minus}1}) and 86.71kcal/mol (30328.5cm{sup {minus}1}). With the same method the triplet dissociation transition state lies 92.4kcal/mol (32300cm{sup {minus}1}) above the ground state. Consequently, the activation energy for the dissociation reaction of H{sub 2}CO on the triplet surface is determined {ital ab initio} to be 18.9{endash}20.1kcal/mol (6620{endash}7040cm{sup {minus}1}) (including an estimated error bar of 1.2kcal/mol or 420cm{sup {minus}1}). The zero-point vibrationally corrected exit barrier height is predicted to be 4.9{endash}6.1kcal/mol (1710{endash}2130cm{sup {minus}1}). These newly predicted energies are consistent with the recent experimental observations by the Moore group at University of California-Berkeley (1987) and by the Wittig group at University of Southern California (1997). {copyright} {ital 1998 American Institute of Physics.}
- OSTI ID:
- 615391
- Journal Information:
- Journal of Chemical Physics, Vol. 108, Issue 13; Other Information: PBD: Apr 1998
- Country of Publication:
- United States
- Language:
- English
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