E.-G. NIEMANN AMI 3’1. KLENERT
3766
bcam, imaged on thc cxit slit of the monoclhromator, is directed back through thc monochromator and optical system to align the components beyond the samplc cell. Because of the high doses absorbed in the sample, a cooling water jacket surrounds the sample cell. In addition, buildup of interfering radiation products is rcduccd by a flow system which rapidly charigcs the solution in thc sample cell during the run.
Results Tests of this stroboscopic pulse-radiolysis system are currently in progrcss. Beam diameters less than 5 mm havc been measured with polyvinyl chloride and perspex HX sheets. A dosc of over 10 l. Densitometer tracks of the streak spectrum in Figure 4: a, t r a m at eonstant time as a function of wavelength; b, traces at canstant wavelength as a function of time after irradiation (zero position shifted). (3) Osrarn SI30 250 W. (4) Steinheil Universal Spectrograph. //3.5. (5) Ilford HI?% (G) H. W. S e i b l d and E&.
Niernnnn. to be published.
T. FELDMANN AND A. TREININ
3768 strong transient absorptions are observed in the range from 390 to 440 nm. The evaluation of this type of spectra is done by densitometer measurement,s along the X and the t axis as well. Some registration tracks of the hydroquinone photolysis spectrum are assembled in Figure 5 . I n part a, absorption maxima at 428 and 404 nm are clearly recognizable which are due to the p-hydroxyphenoxyl r a d i ~ a l . ~ The absorption curve E,(X) of the transient products can be calculated easily by forming the difference between the film density readings before and at time intervals i after irradiation (Xo(X) - &(A)) and dividing this by the gradation curve y(X) of the emulsion
Registrations over time at constant wavelengths are presented in Figure 5b. As is t o be expected, the tracks for 402 and 426 nm yield identical radical half-life
values of about 75 psec. The absorptions of the p-hydroxyphenoxyl radical are superimposed, however, by a long-lived absorption which is seen most clearly in the 381-nm curve. The origin of this absorption could not yet be clarified. For parallel investigations by flash photolytic and pulse radiolytic methods, the system described will be complemented by the addition of a flash X-ray tube. This device, which is still in the test stage, is operated with a 160-kV condenser bank and produces X-ray pulses of O.l-psec duration. The equipment is constructed to give 1 krad per pulse inside the irradiation cuvette. Together with the z-pinch light source and the method of kinetic absorption spectroscopy, it will form a simple and compact arrangement for the flash photolytic and pulse radiolytic investigation of biophysical problems. (7) H. I. Joschok and L. I. Grossweiner, J.Amer. Chem. Soc., 88, 3261 (1966).
I- Photosensitized Reactions in Metaphosphate Glass by T. Feldmann and A. Treininl Department of Physical Chemistry, Hebrew University, Jerusalem, Israel
(Received M a y 7, 1968)
The photooxidation of C1- and Br- in metaphosphate (MP) glass could be sensitized by I-. The reaction was investigated by optical and esr methods. The mechanism proposed involves energy transfer from excited I- to a phosphate polymer, which subsequently dissociates to form the MP color centers. The oxidation of X- is a dark reaction whereby MP holes are scavenged by halide ions, and X atoms are converted to XZradicals. The esr of Clz- in glass is analyzed. The primary processes involving excited I- are discussed and an exciton-type mechanism is proposed for the energy transfer.
The halide ions X- have no excited states in the gas phasej2 but as shown by spectroscopic and photochemical experiments, such states (so called CTTS states) do exist in solution.3 Their natural lifetimes, estimated from their integrated absorption bands,4aare about 10-6 sec, but the actual lifetimes are much shorter.4b Dissociation to X esol- and deactivation to ground state are the competing radiationless processes in liquid solutions. The activation energy of dissociation is higher (by ea. 5 kcal for I- and Br- in aqueous solution) and this by itself can explain their low dissociation yield in ices at 77OK.6 (In alkaline ices, trapped electrons could not be detected.6) The mechanisms of these processes are not clear. Dissociation of X-* may involve diffusion of X from excitation ~ i t e . ~ bI n this case dissociation should be hampered in
+
The Journal of Physical Chemistry
rigid matrices even at room temperature. Still, efficient photolysis of I- and Br- does occur in boric acid7 and metaphosphates glasses. In the first case this may (1) On leave of absence a t the Department of Chemistry, Brandeis University, Waltham, Mass. 02154. (2) R. S. Berry, C. W. Reimann, and G. N. Spokes, J . Chem. Phys., 37, 2278 (1962). (3) For a recent review, see C. K. Jdrgensen, “Halogen Chemistry,” Vol. 1, Academic Press, New York, N. Y., 1967, p 280. (4) (a) J. Jortner and A. Treinin, Trans. Faraday Soc., 58, 1503 (1962); (b) J. Jortner, M. Ottolenghi, and G. Stein, J. Phys. Chem., 6 8 , 247 (1964). (5) P. N. Moorthy and J. J. Weiss, J. Chem. Phys., 42, 3121 (1965). (6) P. B. Ayscough, R. G. Collins, and F. S. Dainton, Nature, 205, 965 (1965). (7) A. Zaliouk-Gitter and A. Treinin, J. Chem. Phys., 42, 2019 (1965). (8) T. Feldmann and A. Treinin, ibid., 47, 2754 (1967).
