Dissociation dynamics of CH3I in electric spark induced breakdown revealed by time-resolved laser induced breakdown spectroscopy

- Emission of electric spark dissociation of CH3I is similar to its fs LIBS.
- We use fs laser induced breakdown as a simulation for electric spark dissociation.
- The I2 molecule formation is directly observed in the time-resolved LIBS.
- Bimolecular collision of I∗ and CH3I is responsible for the formation of I2.

The electric discharge spark dissociation of gas CH3I is found to be similar to its femtosecond laser photodissociation. The almost identical spectra of the two processes show that their initial ionization conditions are very similar. The initial ionization followed by molecular fragmentation is proposed as the dissociation mechanism, in which the characteristic emissions of I+, CH3, CH2, CH, H, and I2 are identified as the dissociation products. The emission band of 505 nm I2 is clearly observed in the time-resolved laser induced breakdown spectroscopy (LIBS). The dynamic curve indicates that I2∗ molecules are formed after the delay time of ∼4.7 ns. The formation of I2∗ molecule results from the bimolecular collision of the highly excited iodine atom I∗(4P) and CH3I molecule. This dynamical information can help understand the process of electric discharge spark dissociation of CH3I.