Publications
The addition of hydrogen atoms to diacetylene and the heats of formation of i-C4H3 and n-C4H3
In this article, we discuss in detail the addition of hydrogen atoms to diacetylene and the reverse dissociation reactions, H + C{sub 4}H{sub 2} {leftrightarrow} i-C{sub 4}H{sub 3} (R1) and H + C{sub 4}H{sub 2} n-C{sub 4}H{sub 3} (R2). The theory utilizes high-level electronic structure methodology to characterize the potential energy surface, Rice-Ramsperger-Kassel-Marcus (RRKM) theory to calculate microcanonical/J-resolved rate coefficients, and a two-dimensional master-equation approach to extract phenomenological (thermal) rate coefficients. Comparison is made with experimental results where they are available. The rate coefficients k{sub 1}(T, p) and k{sub 2}(T, p) are cast in forms that can be used in chemical kinetic modeling. In addition, we predict values of the heats of formation of i-C{sub 4}H{sub 3} and n-C{sub 4}H{sub 3} and discuss their importance in flame chemistry. Our basis-set extrapolated, quadratic-configuration-interaction with single and double excitations (and triple excitations added perturbatively), QCISD(T), predictions of these heats of formation at 298 K are 130.8 kcal/mol for n-C{sub 4}H{sub 3} and 119.3 kcal/mol for the i-isomer; multireference CI calculations with a nine-electron, nine-orbital, complete-active-space (CAS) reference wavefunction give just slightly larger values for these parameters. Our results are in good agreement with the recent focal-point analysis of Wheeler et al. (J. Chem. Phys. 2004, 121, 8800-8813), but they differ substantially for {Delta} H{sub f 298}{sup 0}(n-C{sub 4}H{sub 3}) with the earlier diffusion Monte Carlo predictions of Krokidis et al.