The rate constant kfwd for the dechelation, migration and β-hydrogen transfer steps of ITG decomposition are calculated from the reactions barriers for these reactions through Eq. ( ), with data available in Table . The transition state barrier for the dechelation step (R1a/R2a/R3a) is mostly unchanged after repeated decomposition. At 200 °C, for example, kfwd is equal to 9.63x10 -2 /3.36x10 0 /4.14x10 -3 for R1a/R2a/R3a steps, respectively. Thus, the rate constant exhibits little variation for these steps at constant temperature.