Conformer-Specific Photodissociation Dynamics of CF₂ICF₂I in Solution Probed by Time-Resolved Infrared Spectroscopy

Abstract

The photodissociation dynamics of CF 2 ICF 2 I in solution was investigated from 0.3 ps to 100 μs, after the excitation of CF 2 ICF 2 I with a femtosecond UV pulse. Upon excitation, one I atom is eliminated within 0.3 ps, producing a haloethyl radical having a classical structure: anti-CF 2 ICF 2 and gauche-CF 2 ICF 2 . All the nascent gauche-CF 2 ICF 2 radicals reacted with the dissociated I atom within the solvent cage to produce a complex, I 2 ••C 2 F 4 , in <1 ps. The quasi-stable I 2 •• C 2 F 4 complex in CCl 4 (CH 3 CN or CD 3 OH) further dissociated into I 2 and C 2 F 4 with a time constant of 180 ± 5 (46 ± 3) ps. Some of the anti-CF 2 ICF 2 radicals also formed the I 2 ••C 2 F 4 complex with a time constant of 1.5 ± 0.3 ps, while the remaining radicals underwent secondary elimination of I atom in a few nanoseconds. The time constant for the secondary dissociation of I atom from the anti-CF 2 ICF 2 radical was independent of the excitation wavelength, indicating that the excess energy in the nascent radical is relaxed and that the secondary dissociation proceeds thermally. The formation of the I 2 ••C 2 F 4 complex and the thermal dissociation of the anti-CF 2 ICF 2 radical clearly demonstrate that even a weakly interacting solvent plays a significant role in the modification and creation of reaction.

Photodissociation Dynamics of Nitric Oxide from N-Acetylcysteine- or N-Acetylpenicillamine-bound Roussin’s Red Ester

“…Broader absorption bands for radical compounds were also observed in other reactions in the solution. 28,29 The amplitude of the basis spectrum, that is, the sum of the integrated area of the absorption bands in the basis spectrum, is proportional to the population of the corresponding species. 47 Consequently, the concentration of the corresponding compound can be determined using the extinction coefficients of the absorption bands for each compound.…”

“…The details of the TRIR spectrometer used have been described elsewhere. , Briefly, a commercial Ti:sapphire amplifier (Spitfire, Spectra Physics) pumped two home-built optical parametric amplifiers (OPAs). A tunable mid-IR pulse (100 fs, 160 cm –1 , 1 μJ) was generated by difference frequency mixing of the near-IR signal and idler pulses of one OPA.…”

“…Time-resolved (TR) spectroscopy, in particular, pump-probe spectroscopy, has been widely applied in the study of the dynamics of photoexcited molecules. − In femtosecond TR pump-probe spectroscopy, an equilibrium sample is excited by an intense femtosecond laser pulse (pump), and the subsequent reaction is monitored by collecting transient spectra sequentially with another femtosecond laser pulse (probe). TRIR spectroscopy uses an IR probe pulse to measure a series of transient vibrational spectra of the photoexcited sample. , The vibrational spectrum is sensitive to the structure of the compound, enabling the assignment of reaction intermediates, thereby helping determine the detailed dynamics of the photoexcited molecule.…”

Structural Dynamics of C2F4I2 in Cyclohexane Studied via Time-Resolved X-ray Liquidography

“…The photoexcitation of haloalkanes at ultraviolet wavelengths induces an electronic transition corresponding to the n → σ* transition of a carbon–halogen bond, leading to the dissociation of halogen atoms [ 1 , 2 ]. This photoinduced dissociation has served as an excellent model system to study reaction dynamics due to their simple molecular structures [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ]. The structures of reaction intermediates of haloalkane photodissociation are relevant to the stereochemical control of the products of the halogen elimination reaction of haloalkanes.…”

“…In solution-phase reactions, the solvent influences the energetics and the dynamics of solute molecules through solute-solvent interactions [2][3][4][5][6][7][8]72,73]. Therefore, to understand the mechanism of a chemical reaction in solution, it is essential to consider the effect of solutesolvent interactions on the reaction mechanism [12][13][14][26][27][28][29][30]. According to a previous TRXL study of C 2 H 4 I 2 in cyclohexane, the C 2 H 4 I• radical has a bridged structure as for the same reaction in methanol, but its dynamics and mechanism vary substantially depending on the type of solvent [10][11][12].…”