Photodissociation dynamics of the triiodide anion (I3−)

Abstract

The spectroscopy and dissociation dynamics of I 3 Ϫ were investigated using fast beam photofragment translational spectroscopy. The photofragment yield of I 3Ϫ from 420 to 240 nm was measured, yielding two broadbands at the same energies as in the absorption spectrum of I 3 Ϫ in solution. Photodissociation dynamics measurements performed with two-particle time-and-position sensitive detection revealed two product mass channels having photofragment mass ratios of 1:2 and 1:1. Both channels were seen at all photolysis wavelengths. Translational energy distributions show that the 1:2 products are from a combination of I( 2 P 3/2 )ϩI 2 Ϫ and I*( 2 P 1/2 )ϩI 2 Ϫ . The 1:1 mass channel is from symmetric three-body dissociation to I Ϫ ϩ2I.

Two- and three-body photodissociation of gas phase I3−

“…The new results provide evidence for I Ϫ ϩI 2 (A 3 ⌸ 1u ) production following excitation of the lower band, which accounts for some of the discrepancies in the branching ratios between the two earlier photodissociation studies. 1,2 In addition, we find no evidence for production of I*ϩI 2 Ϫ (X 2 ⌺ u ϩ ) from excitation of the lower band, nor of IϩI 2 Ϫ (X 2 ⌺ u ϩ ) from the upper band, in contrast to our earlier work. Finally, we obtain considerably more information on the decay dynamics of the three-body channels.…”

“…33 The new design presents several advantages, described in more detail in the following section, over that used in the work of Choi et al 1 In particular, the new detector is not restricted to the detection of only two fragments per laser shot, and charged fragments can be detected directly. These features result in better characterization of both the two-and three-body dissociation channels of I 3 Ϫ .…”

“…While much of the original work on I 3 Ϫ was performed in condensed phases, several recent gas phase experiments have provided significant insight into the energetics, spectroscopy, and photodissociation dynamics of this linear, closed-shell anion. However, experiments performed in different laboratories 1,2 suggest that significant questions remain regarding the primary photochemistry of the tri-iodide anion, particularly concerning the branching ratios among available product channels. In this paper, the photodissociation dynamics of I 3 Ϫ are investigated with an upgraded instrument in order to resolve this and other issues.…”

“…Choi et al 1 carried out further investigations of the photodissociation spectroscopy and dynamics of gas phase I 3 Ϫ in the range of 240-420 nm. The photofragment yield ͑PFY͒ spectrum of I 3 Ϫ revealed two intense features with maxima at 290 and 360 nm, in accordance with solution phase work.…”

“…There are numerous decay pathways energetically accessible following excitation in the UV: →I Ϫ ͑ 1 S ͒ϩI͑ 2 P 3/2 ͒ϩI*͑ 2 P 1/2 ͒ D 0 ϭ3.80Ϯ0.06 eV ͑7͒ Time-and frequency-domain experiments on the photodissociation and photoelectron spectroscopy of I 3 Ϫ have been carried out in our laboratories. 1,30,31 The time-resolved photodissociation of gas phase I 3 Ϫ at 390 nm was studied by Zanni et al 30 using femtosecond photoelectron ͑FPE͒ spectroscopy. Excitation of I 3 Ϫ at this wavelength resulted in the production of I Ϫ and I 2 Ϫ with approximately equal yields.…”