Temperature Dependent Absorption Spectra of Br⁻, Br₂^•−, and Br₃⁻ in Aqueous Solutions

Abstract

The absorption spectra of Br(2)(•-) and Br(3)(-) in aqueous solutions are investigated by pulse radiolysis techniques from room temperature to 380 and 350 °C, respectively. Br(2)(•-) can be observed even in supercritical conditions, showing that this species could be used as a probe in pulse radiolysis at high temperature and even under supercritical conditions. The weak temperature effect on the absorption spectra of Br(2)(•-) and Br(3)(-) is because, in these two systems, the transition occurs between two valence states; for example, for Br(2)(-) we have (2)Σ(u) → (2)Σ(g) transition. These valence transitions involve no diffuse final state. However, the absorption band of Br(-) undergoes an important red shift to longer wavelengths. We performed classical dynamics of hydrated Br(-) system at 20 and 300 °C under pressure of 25 MPa. The radial distribution functions (rdf's) show that the strong temperature increase (from 20 to 300 °C) does not change the radius of the solvent first shell. On the other hand, it shifts dramatically (by 1 Å) the second maximum of the Br-O rdf and introduces much disorder. This shows that the first water shell is strongly bound to the anion whatever the temperature. The first two water shells form a cavity of a roughly spherical shape around the anion. By TDDFT method, we calculated the absorption spectra of hydrated Br(-) at two temperatures and we compared the results with the experimental data.

Visible Light Driven Bromide Oxidation and Ligand Substitution Photochemistry of a Ru Diimine Complex

“…Pulsed laser excitation of 50 μM tribromide and 50 μM bromide in acetonitrile produced an intermediate consisting of two positive absorptions centered at 370 and 770 nm, along with a tribromide ground state bleach below 340 nm (Figure b). The positive absorption bands were consistent with previous reports of Br 2 •– in aqueous solutions . Representative kinetic data monitored at 770 nm (Figure b inset) revealed a biphasic feature, a growth that could not be time-resolved (>10 8 s –1 ), and a slower growth that reached maximum in several microseconds.…”

“…•− in aqueous solutions. 30 Representative kinetic data monitored at 770 nm (Figure 1b inset) revealed a biphasic feature, a growth that could not be time-resolved (>10 8 s −1 ), and a slower growth that reached maximum in several microseconds. The amplitudes of both features were equal.…”

Picosecond Pulse Radiolysis of Direct and Indirect Radiolytic Effects in Highly Concentrated Halide Aqueous Solutions

“…Recently, the rate constant of Br 2 À• decay was also reported at different temperatures. 40 In our case, the main difference is that the concentrations of the two studied solutions are very high and the measurements are performed on the picoseconds range. Considering the two kinetics of the solvated electron reported in Figure 2a, we did not observe any difference between them (except the amplitude) and we may conclude that there is no effect of Br À concentration on the chemical process induced by radiation.…”

Sequential radiation chemical reactions in aqueous bromide solutions: pulse radiolysis experiment and spur model simulation

“…Zehavi and Rabani pointed out the absorption observed in the UV domain in aqueous bromide solutions would be attributed to Br 3 À . 13 25 Thus, most discussions in past reports are based on yields of nal products aer irradiation.…”