Sir:Since the first e.p.r. observation by Ingram? and his colleagues on the photolytic formation of free radicals in hydrogen peroxide a t liquid nitrogen temperature, a considerable amount of research has been done on the identification of paramagnetic species produced under these or similar conditions. Preparation of the samples for e.p.r. examination has been performed either by condensation a t liquid nitrogen temperature of the products of electric discharge in various gaseous mixtures containing H 2 0 2 or by direct photolysis of aqueous H20s solutions frozen in liquid nitrogen.2,5,6 I n all the cases reported, the e.p.r. spectrum seems to represent the same species, believed by most authors to be the H 0 2 radical. However, Kaitmazov and Prokhorov5 indicate !hat: (1) ultraviolet irradiation (with X >2fi00 A,) of Hz02 may result only in the breakage of the HO-OH bond, and (2) no secondary reactions occur during photolq sis, since the change of H202 concentration in the range from 3-987, does not affect the spectrum. Thus, according to Kaitmazov and Prokhorov, the e.p.r. spectrum obtained by H202 photolysis a t liquid nitrogen temperature must be derived from OH radicals. The present report summarizes the results of e.p.r. experiments carried out with H202 solutions irradiated by TP-particles and ultraviolet light a t liquid nitrogen temperature Irradiation by Tp-Particles.-6 -11 H 2 0 2 solution was tritiated with T20 to an activity of 0.3 c./'ml. and frozen in glass sample tubes in liquid nitrogen. Tritium has been chosen as an internal source of radiation since, as reported previously,' i t allows one to avoid the background of irradiated glass in the e.p.r. spectrum. The resulting e.p.r. spectrum (Varian V4500, X-band e.p.r. spectrometer) shown in Fig. 1 9 , is very similar to the spectra reportedj for H?OZ irradiated by ultraviolet light and consists essentially of a fairly broad band, poorly resolved into two peaks, with separation of about 12 gauss. This spectrum is, however, distinctly different from that usually attributed to OH radicals and obtained by irradiation with CoiiO ?-rayss or Ta-particles' of pure HzO ice.The e.p.r. spectrum produced by T,!j'-particle: in H20 ice at liquid nitrogen temperature is shown in Fig. 1B. Lipart from their spectral appearan :e, radicals , ?, (produced in H20s) and B (in H 2 0 ) di; 'er markedly in thermal stabilities. , I s shown in I ig.(1) Supported b y a grant from the Sational Research Counc of C m a d s .

No abstract

By using tritium as an internal source of radiation, electron spin resonance spectra may be obtained for samples contained in glass without the usual disturbing effects due to irradiated glass. The production of OH and OD radicals in tritiated H(2)O and D(2)O ice may be readily demonstrated with this technique.