Theoretical Investigation of the Mechanisms and Kinetics of the Bimolecular and Unimolecular Reactions Involving in the C4H6 Species

A theoretical study of the mechanisms and kinetics for the C4H6 system was carried out using ab initio molecular orbital theory based on the CCSD(T)/CBS// B3LYP/6-311++G(3df,2p) method in conjunction with statistical theoretical variable reaction coordinate transition-state theory and RRKIVI/ME calculations. The calculated results indicate that buta-1,3-diene, but-1-yne, and C4H5 + H can be the major products of the C-3 + C-1 reaction, while CCH2 + C(2)H(4 )and C4H5 + H play an important role in the C-2 + C-2 reaction. In contrast, the C4H6 fragmentation giving rise to C-3 + C-1 and C4H5 + H becomes the key reaction paths under any temperature and pressure. The rate constants for the system have been calculated in the 300-2000 K temperature range at various pressures for which the C-2 + C-2 -> C(4)H(6 )high-P limit rate constant, 10.24 X 10(14)T(-0.51 )cm(3)/mol/s, agrees well with the measured value of Hidaka et al., 9.64 X 10(14 )T(-0.5)cm(3)/mol/s. Also, the high-P limit rate constants of the channels but-2-yne -> 2-C4H5 + H and C-3 + C-1 -> C4H6, being 1.7 X 10(14) exp(-351.5 kJ.mol(-1)/RT) s(-1) and 5.07 X 10(13) exp(0.694 kj.mol(-1)/RT) cm(3)/mol/s, are in good agreement with the available literature data 5 X 10(14 )exp(-365.3 kJ.mol(-1)/RT) s(-1) and 4.09 X 10(13 )exp(1.08 kJ.mol(-1)/RT) cm(3)/mol/s reported by Hidaka et al. and Knyazev and Slagle, respectively. Moreover, the 298 K/50 Torr branching ratios for the formation of buta-1,2-diene (0.43) and but-1-yne (0.57) as well as the total rate constant 5.18 x 10(13) cm(3)/mol/s of the channels C-3 + C-1 -> buta-1,2-diene and C-3 + C-1 -> but-1-yne are in excellent accord with the laboratory values given by Fahr and Nayak, being 0.4, 0.6, and (9.03 +/- 1.8) x 10(13 )cm(3)/mol/s, respectively. Last but not least, the rate constants and branching ratios for the C4H6 dissociation processes in the present study also agree closely with the theoretically and experimentally reported data.

Automated summary

Theoretical study on the mechanisms and kinetics of the C4H6 system shows the major products and key reaction paths in different reactions. The calculated results are in excellent agreement with experimental data.