Multiphoton ionization and dissociation dynamics of Freon-113 induced by femtosecond laser pulse

Abstract

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.

Photodissociation and formation of an ion‐pair in CH2FCl (HCFC‐31)

“…The rate constants for this reaction have been given by Atkinson et al in the temperature range 240-300 K. 14 Despite the scarcity of photochemical studies concerning HCFC-31, photodissociation have been employed to detect some halogenated hydrocarbons and freons. [15][16][17] The laser induced breakdown spectroscopy (LIBS), combined with the single particle aerosol mass spectrometry (SPAMS) have been used for the online detection of halogen lines due to the photodissociation of Halon 2402, Freon R11, iodomethane 15 and C 2 H 4 BrF 16 in the atmosphere. The time-of-flight mass spectrometry coupled with velocity map imaging technique has been used to study the multiphoton ionization and photodissociation dynamics of Freon-113 induced by femtosecond laser pulse.…”

“…The time-of-flight mass spectrometry coupled with velocity map imaging technique has been used to study the multiphoton ionization and photodissociation dynamics of Freon-113 induced by femtosecond laser pulse. 17 18 Despite its low ozone depletion potential (ODP) of 0.019, 19 the following four reasons make HCFC-31 a substance of great atmospheric importance 3,4 : (i) its 20-year cumulative emission (from 1978 to 2019) of 10.6 Gg; (ii) its unknown purposeful end-use; (iii) an emission which amounts to 0.8 Gg in 2020 and (iv) an atmospheric lifetime of 1.4 years.…”

Photodissociation of IBr molecule in the wavelength range 440–680 nm

“…Experimenters and theoreticians have been occupied for decades in a series of studies of the dissociation of IBr molecules. Employing a state-of-the-art ion imaging spectrometer operated under the best conditions for velocity mapping [16][17][18][19][20], Wrede [21] studied the dissociation of jet-cooled IBr molecules at excited state wavelengths in the range 440-685 nm. The photodissociation dynamics of IBr has been theoretically researched by Zhang [22] at excited state wavelengths in the range 450-540 nm by a precise one-dimensional (1D) timedependent dynamical simulation technique [23][24][25][26][27][28][29][30].…”