The ozone layer which absorbs harmful solar UV radiation is an essential umbrella for human. However, a large number of exhausts of Freon released by human activity into the atmosphere pose a great threat to the ozone layer. The UV sunlight radiation induced Freon dissociation produces chlorine radicals, which are found to be the main culprit for destroying the atmospheric ozone. In this paper, multiphoton ionization and dissociation dynamics of Freon-113 (CF2ClCFCl2) induced by femtosecond laser pulse are studied by time-of-flight mass spectrometry coupled with velocity map imaging technique. Fragment mass spectra of Freon-113 are measured by time-of-flight mass spectrometry. No parent ions are discovered in the time-of-flight mass spectra, and all the detected ions are from the fragmentation induced by the laser pulse. Daughter ions CFCl2+, CF2Cl+, C2F3Cl2+ are found to be the three major fragmentation ions in the multi-photon ionization and dissociation. Several photodissociation channels are discussed and concluded by further analysis and calibration (via the ratio of mass to charge) of the measured time-of-flight mass spectra. Three main photodissociation mechanisms are found as follows: 1) C2F3Cl3+→C2F3Cl2++Cl with breaking C--Cl bond and directly producing the Cl radical; 2) C2F3Cl3+ →CFCl2++CF2Cl with breaking the C--C; 3) C2F3Cl3+ →CF2Cl++CFCl2 with breaking the C--C bond. Ion images of the three main fragments C2F3Cl2+, CFCl2+ and CF2Cl+ are measured by the velocity map imaging setup. The speed distributions of these three fragment ions are obtained from the velocity map imaging. The speed distribution of C2F3Cl2+ with breaking C--Cl bond can be fitted by two Gaussian distributions while the speed distributions of both CFCl2+ and CF2Cl+ with breaking the C--C bond can be well fitted by one Gaussian distribution. The different fittings reflect different production channels. The detailed photodissociation dynamics is obtained by analyzing the kinetic energy distribution and angular distribution of the fragment ions. Additionally, density functional theory calculations on high-precision level are also performed on photodissociation dynamics for further analysis and discussion. An in-depth understanding of dissociation dynamics of freon can provide theoretical reference and experimental basis for further controlling the dissociation process that can do destruction to the ozone layer.
Depletion of atmospheric ozone layers is more and more serious. Alkyl halides dissociate under the solar UV radiation with the product of free halogen atoms, which greatly damages the ozone layer and is the main culprit for the depletion of ozone layers. In this paper, methyl iodide is chosen as a calibration system of velocity map imaging. Velocity map images of iodine atom I (2P3/2) at different focus voltages are obtained in the dissociation of methyl iodine under an UV radiation of ~266 nm by techniques of velocity map imaging and REMPI (Resonance Enhanced Multiphoton Ionization). The magnification factor N of velocity map imaging system is measured to be 1.13. Photodissociation dynamics of 1, 4-C4H8BrCl under an UV radiation of ~234 nm is investigated on this velocity map imaging system. The speed and angular distributions of the fragments Br(2P3/2) and Br* (2P1/2) atoms in the dissociation are obtained and analyzed. Experimental results suggest that the dissociation of 1, 4-C4H8BrCl to both Br(2P3/2) and Br* (2P1/2) atoms under an UV radiation of ~234 nm happens promptly along the C-Br bond via repulsive surfaces after excitation. The anisotropy coefficient values are obtained from angular distributions of imaging of the fragments Br (2P3/2) and Br* (2P1/2) atoms, by which the ratio between perpendicular transition and parallel transition for those two dissociation channels are calculated. In addition, photodissociation mechanisms of CH2BrCl, 1, 2-C2H4BrCl, 1, 3-C3H6BrCl and 1, 4-C4H8BrCl at an UV radiation of ~234 nm are compared, and the dependences of dissociation mechanisms of dihalogen alkyl compounds on size of the alkyl radical are obtained.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.