Changmai Rabu Ranjan, Daimari Samsung Raja, Yadav Anand Kumar, Sarma Manabendra
Department of Chemistry, Indian Institute of Technology, Guwahati, Assam - 781039, India.
Phys Chem Chem Phys. 2024 Sep 11;26(35):23363-23371. doi: 10.1039/d4cp01643b.
The atmospheric oxidation of 1,1-dichloro-1,3,3,3-tetrafluoropropane, HCFC-234fb (DTP), leads to the formation of harmful radicals, contributing to stratospheric ozone depletion. Thus, a detailed study of the gas-phase oxidation of the first-generation chlorofluorocarbon alternative HCFC-234fb by a reaction with hydroxyl radicals and chlorine atoms is important to understand its harmful effects on the environment. In this work, we have performed quantum chemical calculations to investigate the thermodynamic and kinetic aspects of the titled reaction. The potential energy profile calculated at the CCSD(T)/aug-cc-pVTZ//MP2/cc-pVTZ level of theory shows that the major reaction pathway involves the abstraction of the H-atom from the central carbon atom, C, giving rise to the product radical CFC˙HCClF. The calculated rate-coefficients for the reaction with ˙OH and Cl-atoms are 3.89 × 10 and 2.54 × 10 cm molecule s, respectively, at 298 K and are in accordance with the experimental rate coefficients. The results suggest that the rate-coefficient for the reaction of DTP with ˙OH is two orders of magnitude higher than that with Cl-atoms, indicating greater significance of the former reaction in the atmosphere. With the rate-coefficient values, the lifetime and the radiative efficiency were calculated to be 8.2 years and 0.246 W m ppb, respectively. A 100-year global warming potential (GWP) of 712 was also estimated using the lifetime corrected radiative efficiency value.
1,1 - 二氯 - 1,3,3,3 - 四氟丙烷（HCFC - 234fb，简称DTP）的大气氧化会导致有害自由基的形成，从而加剧平流层臭氧消耗。因此，详细研究第一代氯氟烃替代品HCFC - 234fb与羟基自由基和氯原子反应的气相氧化过程，对于理解其对环境的有害影响具有重要意义。在这项工作中，我们进行了量子化学计算，以研究上述反应的热力学和动力学方面。在CCSD(T)/aug - cc - pVTZ//MP2/cc - pVTZ理论水平下计算得到的势能面表明，主要反应途径涉及从中心碳原子C上夺取氢原子，生成产物自由基CFC˙HCClF。在298 K时，计算得到的与˙OH和Cl原子反应的速率系数分别为3.89×10和2.54×10 cm³ molecule⁻¹ s⁻¹，与实验速率系数相符。结果表明，DTP与˙OH反应的速率系数比与Cl原子反应的速率系数高两个数量级，这表明前者在大气中的反应更为重要。根据速率系数值，计算得到的寿命和辐射效率分别为8.2年和0.246 W m⁻² ppb⁻¹。还使用经寿命校正的辐射效率值估算了100年全球变暖潜能值（GWP）为712。
