Kinetics and energy transfer in the thermal decomposition of 2-methyloxetane and 3-methyloxetane

Abstract

The thermal decomposition of 2-methyloxetane and 3-methyloxetane has been studied between 660 and 760 K in the pressure range 0.01–3 kPa. In the pressure-independent range, rate coefficient expressions log(k^∞₁/s^–1)=(14.53 ± 0.12)–(249.2 ± 2.2 kJ mol^–1)/2.303RT and log(k^∞₂/s^–1)=(15.67 ± 0.17)–(269.8 ± 3.3 kJ mol^–1)/2.303RT were determined for 2-methyloxetane decomposition into C₃H₆+ HCHO (k₁) and C₂H₄+ CH₃CHO (k₂), respectively, while for 3-methyloxetane decomposition into C₃H₆+ HCHO (k₃) the following kinetic parameters were obtained: log(k^∞₃/s^–1)=(15.38 ± 0.27)–(258.7 ± 3.7 kJ mol^–1)/2.303RT. The pressure dependence of the homogeneous decomposition rate and the efficiency of the gas-phase collisional energy transfer have been studied at 743 K. A value of 〈ΔE〉_d= 1500 ± 300 cm^–1 was extracted from the investigation of the pressure dependence of the two-channel decomposition of 2-methyloxetane. Finally, the efficiency of the surface–gas energy transfer has been studied by the ‘variable encounter method’ in the range 750–1100 K. At 750 K the average energy transferred per collision with the wall was determined to be 2600 cm^–1 for both methyloxetanes; however, 〈ΔE′〉 decreased considerably with increasing temperature. The results on the collision efficiencies were discussed and compared with literature data for related molecules.