Resonance enhanced multiphoton ionization time-of-flight (REMPI-TOF) study of tetrachloroethylene photodissociation at 235 nm: Role of bound π-σC-Cl∗ state

Cl‐Radical Formation in UV Photodissociation of Tetrachlorocyclopropene: A REMPI Study

“…Vertical excitation energies were calculated by TD‐DFT method using mpw1pw91 correlation and aug‐cc‐pVTZ basis sets. Though the calculated results at this level do not always match with experimental results, the nature of the transitions and the orbitals involved could be accurately predicted for similar compounds …”

“…It has been observed for photodissociation of saturated or unsaturated chlorinated hydrocarbons at different wavelengths, i. e., 193, 248 and 266 nm, multiple channels may be operative, their contribution depending on the structural features of the parent molecule. Tetrachlorocyclopropene (TCCP) is a very unique molecule, mainly because of the presence of the very small and highly strained cyclopropene ring.…”

“…As discussed in the previous section, the formation of Cl/Cl* in the photodissociation of TCCP near 235 nm seems to be a combination of multiple channels operative from the ground state and the excited states. From the reported literature, it has been observed for photodissociation of saturated or unsaturated chlorinated hydrocarbons at different wavelengths, i. e., 193, 248 and 266 nm, majorly three different channels may be operative. The molecule may dissociate directly from the optically excited repulsive state, as in case of the mono‐unsaturated completely chlorinated straight chain compounds like tetrachlorethylene, trichloroethylene or vinyl chloride.…”

“…Most of these studies report that absorption at 193 nm, leads to excitation to the bound π—π* state, which crosses over to a directly dissociative π—σ* C‐Cl state, resulting in direct C—Cl bond breaking with a large translational energy release. A lower kinetic energy channel was also found to take place from the ground state which gets populated by internal conversion from the π—σ* state. For trichloroethylene and tetrachloroethylene, absorption at 235 nm, however, led to π—σ* C‐Cl transition, and impulsive dissociation from there to release Cl atom with high translation energy.…”

“…These halogenated compounds also play a significant role in the contamination of surface and ground water. In this context, the UV absorption and photodissociation of vinyl chloride, trichloroethylene and tetrachloroethylene have been extensively studied by different research groups and a comprehensive and comparative understanding of the dissociation dynamics of these compounds has been well established . Most of these studies report that absorption at 193 nm, leads to excitation to the bound π—π* state, which crosses over to a directly dissociative π—σ* C‐Cl state, resulting in direct C—Cl bond breaking with a large translational energy release.…”