Investigating the Photodissociation Dynamics of CF2BrCF2I in CCl4 through Femtosecond Time-Resolved Infrared Spectroscopy

The photodissociation dynamics of CF2BrCF2I in CCl4 at 280 +/- 2 K were investigated by probing the C-F stretching mode from 300 fs to 10 mu s after excitation at 267 nm using time-resolved infrared spectroscopy. The excitation led to the dissociation of I or Br atoms within 300 fs, producing the CF2BrCF2 or CF2ICF2 radicals, respectively. All nascent CF2ICF2 underwent further dissociation of I, producing CF2CF2 with a time constant of 56 +/- 5 ns. All nascent g-CF2BrCF2 isomerized into the more stable a-CF2BrCF2 with a time constant of 47 +/- 5 ps. Furthermore, a-CF2BrCF2 underwent a bimolecular reaction with either itself (producing CF2BrCF2Br and CF2CF2) or Br in the CCl4 solution (producing CF2BrCF2Br) at a diffusion-limited rate. The secondary dissociation of Br from a-CF2BrCF2 was significantly slow to compete with the bimolecular reactions. Overall, approximately half of the excited CF2BrCF2I at 267 nm produced CF2BrCF2Br, whereas the other half produced CF2CF2. The excess energies in the nascent radicals were thermalized much faster than the secondary dissociation of I from CF2ICF2 and the observed bimolecular reactions, implying that the secondary reactions proceeded under thermal conditions. This study further demonstrates that structure-sensitive time-resolved infrared spectroscopy can be used to study various reaction dynamics in solution in real time.

Automated summary

The photodissociation dynamics of CF2BrCF2I in CCl4 solution at 280 ± 2 K were studied using time-resolved infrared spectroscopy. The dissociation of I or Br atoms occurred within 300 fs after excitation, forming CF2BrCF2 or CF2ICF2 radicals, respectively. CF2ICF2 further dissociated to CF2CF2 with a time constant of 56 ± 5 ns. g-CF2BrCF2 isomerized to a-CF2BrCF2 with a time constant of 47 ± 5 ps. a-CF2BrCF2 underwent bimolecular reactions with itself or Br in CCl4 solution at a diffusion-limited rate. The secondary dissociation of Br from a-CF2BrCF2 was slower than the bimolecular reactions. Approximately half of the excited CF2BrCF2I produced CF2BrCF2Br, while the other half produced CF2CF2. The excess energies in the nascent radicals thermalized faster than the secondary dissociation of I from CF2ICF2 and the observed bimolecular reactions, indicating that the secondary reactions occurred under thermal conditions. This study highlights the application of structure-sensitive time-resolved infrared spectroscopy in studying real-time reaction dynamics in solution.