Julissa Velasquez


Photo of Julissa Velasquez with a green background
Dr. Paul Marshall
Research Topic: 
Relative Rate Kinetics Of CH3F With Atomic Chlorine
Frequent human contributions to the earth’s atmospheric composition require understanding of kinetics that define atmospheric reactions. Fluoromethane (CH3F (HFC-41)) is an example of halogen compounds that enter the atmosphere because of their industrial use in refrigerants, aerosol, and electronic products. These halogen compounds are degraded by their reactions with radicals, including chlorine atoms (Cl). CH3F and similar industrial compounds are prevalent in the atmosphere, making it essential to understand their reactivity quantitatively. Chlorine (Cl2) and CH3F were used as reactants, with varying quantities of oxygen (O2), to develop the relative rate kinetics of Cl + CH3F chemistry. Using a mercury lamp for UV photolysis of Cl2, an initiation step leads to an intermediate product, the CH2F· radical. This intermediate then continues to the products CH2FCl, an ozone depleting compound by reacting with Cl2, and CHOF by reacting with O2. Fourier-transform infrared (FT-IR) spectroscopy identified initial reactants and tracked products over time at a resolution of 1.0 cm-1. An experimental setup with a total pressure of 750 Torr at 298 K was designed to study competition between the reactions of initially formed CH2F· with Cl2 and O2. Rate constants, a mathematical number that defines the rates of competing reactions, can be quantified for the products CHOF (1) and CH2FCl (2) as the CH3F is consumed. Rate constants for the reactions leading to products (1) and (2) are determined. The data from these experiments using FT-IR spectroscopy will define the ratio between desired versus undesired products being produced in the atmosphere. This work could encourage advances in industrial sustainability and improve our comprehension of species that contribute to ozone depletion and climate change.