Absorption in the far red by I2− and Br2−

Letters to the Editor

587

Int. J. Radiat. Phys. Chem. 1975, Vol. 7, pp. 587-588. Pergamon Press. Printed in Great Britain

Absorption in the far red by Is- and Br~J. H. BAXENDALE,P. SHARPE and M. D. WARD Chemistry Department, University of Manchester, Manchester M13 9PL, England (Received 12 December 1974; in revised form 28 February 1975)

Abstract--The species Br2- in aqueous solution shows absorption in the red with Amax = 730 nm and e = 340 dm3 mo1-1 cm -x compared with analogous I~- absorption Amax = 725 nm and e = 4"2 × 103 dm a tool -1 cm -x. No far red absorption by CI~- or (CNS)~- was observed.

The transient species I2- produced by flash photolysis o f I - or Ia- in water or alcohols tl,2) has absorption bands with maxima at ca. 375 n m and ca. 725 nm, the latter closely resembling the absorption Ofeaq-. We have f o u n d analogous absorption in the far red by Brz- with m a x i m u m at 700 n m in addition to the k n o w n peak at 360 nm. The spectra shown in Figs 1 and 2 were obtained by the pulse radiolysis o f neutral 10 -s m o l d m -a solutions o f I - and B r - saturated with nitrous oxide. In both cases the red and near-U.V, absorptions were found to have identical decay characteristics, indicating that they belonged to the same species as already shown for Is-.

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Fie. 1. Spectrum of I s- obtained by pulse radiolysis of 10-a mol dm -a I - saturated with nitrous oxide. Oscilloscope trace at 700 rim. Assuming t3~ for I s - that E(375) = 1.56x 104 d m a m o l - l c m - 1 , then Fig. 1 gives E(725) = 4-2 x 10 a d m a m o l - l c m -1, and for Br~-, if e(360) = 8300 d m a m o l - l c m -1 as reported t4~, then c(700) = 340 d m S m o l - l c m -1. We were not able to detect absorptions in the red for C12- p r o d u c e d from chloride ion in 0.1 mol d m -a HC104, or for (CNS)~- produced f r o m C N S - , although in both cases the well-known absorptions at 350 and 480 nm, respectively, were present.

588

Letters to the Editor

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FiG. 2. Spectrum of Br2- obtained as for Fig. I from B r - solution saturated with nitrous oxide. Oscilloscope trace at 800 nm. REFERENCES 1. G. DOBSON and L. I. GROSSWEINER, Radiat. Res. 1964, 23, 290. 2. P. FORNIER DE VIOLET, R. BONNEAU and J. JOUSSOT-DUBIEN, Mol. Photoehem. 1973, 5, 61; Chem. Phys. Lett. 1974, 28, 569. 3. L. I. GROSSWEINER and M. S. MATHESON, J. phys. Chem. 1957, 61, 1089. 4. B. ~ER~EK, Int. J. Radiat. Phys. Chem. 1972, 4, 25.

Int. J. Radiat. Phys. Chem. 1975, Vol. 7, p. 588. Pergamon Press. Printed in Great Britain

ERRATUM F. J. DE HEER: Superexcited states of molecules produced by electron impact. Int. J. Radiat. Phys. Chem. 1975, 7, 137-153. O n p. 144: M o r e r e c e n t m e a s u r e m e n t s o f B a c k x a n d V a n d e r W i e l (21) i n d i c a t e o n l y s u p e r e x c i t e d s t a t e s f r o m single, b u t n o t f r o m m u l t i p l e e l e c t r o n e x c i t a t i o n .