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The structure and energetics of the HCN → HNC transition state

✍ Scribed by Timothy J. Lee; Alistair P. Rendell

Publisher
Elsevier Science
Year
1991
Tongue
English
Weight
644 KB
Volume
177
Category
Article
ISSN
0009-2614

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✦ Synopsis

The optimum geometries and quadratic force constants of HCN, HNC and the transition state connecting them have been determined at the single and double excitation coupled<luster (CCSD) and CCSD(T) levels of theory. Energy differences were evaluated using the CCSD and CCSD(T) methods in conjunction with large atomic natural orbital basis sets containing g-type basis functions on the heavy atoms and f-type functions on hydrogen. The most reliable structure obtained for the transition state hasbond distances of 1.194, 1.188 and 1.389 A for r,, rCH and rPtH, respectively. Including a correction for zero-point vibrational energies, the transition state is predicted to be 44.6 + 1 .O kcal/mol above the HCN isomer, while HNC is predicted to be 14.4 + 1.0 kcal/mol above HCN. The latter value is in excellent agreement with the most recent experimental determination (14.8 +2.0 kcal/mol).

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