State-selective photofragment imaging of iodine atoms via photodissociation of CF3I at 277 nm

Abstract

The multiplet state distribution of O(3 P J ) produced in the 193 nm photodissociation of SO2The photodissociation of CF 3 I cooled in a supersonic molecular beam has been investigated at 277 nm by state-selective photofragment imaging. Fragmented iodine atoms of two spin-orbit states are state-selectively ionized and projected onto a two-dimensional position-sensitive detector, to obtain their speed and angular distribution. The anisotropy parameter for an excited iodine atom I*( 2 P 1/2 ), ␤(I*), is found to be 1.83 and is consistent with a dissociation lifetime in the order of 150-350 fs from rotational correlation function. Contrary to earlier reports, the parallel-like distribution for the ground state iodine atom I( 2 P 3/2 ) at this wavelength, shows a more favorable curve-crossing dissociation path ͑68%͒ from 3 Q 0 to 1 Q 1 and a less favorable direct dissociation path ͑32%͒ from 3 Q 1 . The recoil energy distribution of I is found to be broader than that of I* and is correlated with a variety of energy disposal channels by an e symmetry vibration at the crossing point. The results are compared with previous works, and the strong photon energy dependence of the energy partitioning in CF 3 ϩI* channel and curve crossing are interpreted in terms of the final state interaction and curve crossing probability, respectively.

Time-resolved high-harmonic spectroscopy of the photodissociation of CH3I and CF3I

“…The time constants measured by high-harmonic spectroscopy fall within the 150-350 fs interval for the photodissociation time inferred from fragment anisotropies in Ref. [30]. In the near future, the temporal resolution of the experiment will be improved using temporally compressed 267 nm pulses to study the dynamics at the conical intersection that is expected to be reached ∼20 fs after photoexcitation.…”

“…In the case of CF 3 I, the time scale of dissociation following excitation to the A band has not been reported but a time span of 150-350 fs has been estimated from the anisotropy factor of the photofragments [30]. In addition several simultaneously occurring multiphoton processes related to the A-band photodissociation have been observed [31].…”

Resolved (v1, v2 = 1) Combination Vibrational States of CF3 Fragments in the Photofragment Translational Spectra of CF3I

“…In the I* channel, the distribution was peaking around v 1 = 6, higher than their theoretical result of peaking at v 1 = 4 or 5. Many groups have performed on the CF 3 I photodissociation at different wavelengths. − ,− For the high resolution experiments with vibrational peaks resolved, Felder and Wang et al studied the photodissociation of CF 3 I at 248 nm, and got the 701 cm –1 (ν 1 ) states resolved TOF spectrum in the I* channel with the highest peak at v 1 = 4 and 5, respectively. With the velocity map ion imaging technique, Pratt’s group got 701 cm –1 (ν 1 ) state resolved images on the CF 3 I photodissociation between 304 and 277 nm and also at 266 nm .…”

UV photodissociation dynamics of iodobenzene: Effects of fluorination

“…The UV photophysics of other alkyl iodides (e.g., C 2 H 5 I, 6-8 C 3 H 7 I, 7,9 and fluorinated analogues such as CF 3 I (Refs. 8, [10][11][12] have been studied less thoroughly, but the available data suggest broadly similar dissociation dynamics.…”