N, K. BRIDGE AND & S. !I RIATHESON .
1280
Vol. 64
THE FLASH PHOTOLYSIS OF HALATE AXD OTI-IER IONS IS SOLUTIOX’ BY N.K. BRIDGE AND M. S. MATHESON Argonne National Laboratory, Argmne, Illinois Received March 4, 1960
The photochemistry of aqueous bromate solutions has been examined by the technique of flash photolysis. Two transients were observed and tentatively identified; a short-lived transient (-10 psec.) absorbing a t 350-390 mp was assigned to BrOa. radical (disappearance probably first order), and a longer lived transient ( ~ msec.) 1 absorbing a t 460 r n M to BrO. radical (disappearance second order). Some experimental evidence in support of these assignments is presented. For example the “BrO.” transient is observed in BrO- solutions. The flash photolysis results are correlated with the steady-state photochemical B-ork of Farkas and Klein.
The spectra and photochemistry of simple ions in solution have been investigated in some detail,2-5 especially since Rabinowitch6 suggested that illumination of ion pair complexes in their electron transfer absorption bands might lead to photochemical reactivity. Farkas and Klein,’ using the well established techniques of conventional photochemistry, studied the ultraviolet decomposition of halate (XOS-) ions in air saturated aqueous solution and found that the main reaction was the formation of hypohalite (XO-) and oxygen. Furthermore, the irradiation of the XOcaused the formation of halide (X-) and halate ions and the evolution of oxygen. In all these cases it was assumed that the primary process of light absorption was the transfer of an electron to the hydration layer. For the halate ion, the detailed reactions postulated for neutral solutions are (X03-H20)
+ light
(XOs.Hz0.) -: electron transfer (1) (XOJ.HZO.)- --+ (XOa-HtO) * (2) --f
This excited complex, because of the known exothermicity of the thermal decomposition of the halates to O2 and hypohalite, (5 and 10 kcal., for C103- and BrOs-, re~pectively)~ is then presumed to decompose as (XOa-H10)*
+XO-
+ + H20 0 2
(3)
This explained the observed relatively high XOquantum yield of 0.19 (
