NOTES
382
stances such as p-terphenyl and anthracene which greatly increase the fluorescence of the irradiated solutions. A concentrated solution of m-terphenyl in benzene was shown to have a somewhat lower yield of hydrogen than pure benzene. The present work shows that a similar small decrease in the hydrogen yield is observed for concentrated iodine solutions in benzene. Experimental Ten-cc. samples of Phillips Research Grade (99.93%) benzene were degassed on a high vacuum l i e , sealed and irradiated for from one to four days inside a cylindrical Cow source3 having an intensity of 276,000 R./hr. The sample was then reattached to the vacuum line and the fractions volatile at liquid nitrogen tem erature and at -120” were pumped to a McLeod ga e &r measurement and subsequently to a Saunders-&ylor a paratus for analysis.‘ Based on the rate of oxidation of ~ r r o u sion in the Fricke dosimeter [G(Fe+++)= 15.451 energy was absorbed in the benzene at the rate of 2.38 X 10’7e.v. cc.+ r n h - 1 . It is amumed here that the absorption of energy is proportional to the electron density of material irradiated.
Results and Discussion The yields of hydrogen and CZgas observed for pure benzene and for three concentrated iodine solutions are given in Table I. The gas volatile a t liquid nitrogen temperature was found to be 98 to 99% hydrogen, little or no methane being formed. The radiation yield for hydrogen production from pure benzene observed in the present work using y-radiation is slightly higher than that found by Manion and Burton6 for electron bombardments a t much higher intensities. The Cz gas yield is somewhat lower than the values of 0.0226and 0.0206observed in the electron bombardment studies. TABLEI EFFECTOF IODINE ON THE RADIOLYSIS OF BENZENE Iodine concn., M
Irradiation period, mln.c
Hia produced, moles X 10s
UWdb
U(cr)b
0.0377d ... .037Sd O.OISid ,020 .0360 .0169 ... .037 ,0354 :u)6 .0306 ,0151 Molecules per 100 e.v. c En‘J From a 10-cc. sample. wgy is absorbed in the benzene at the rate of 2.38 X lo1’ Manion and Burton6 gave a yield of 1e.v. m.-l min.-l. (0.0357for Ht and 0.022for C1 for 2.0 MeV. electrons. 0 0
1390 4560 1690 1580 1355
2.07 6.81 2.40 2.21 1.80
It is seen that the dissolved iodine has little effect the hydrogen yield except a t very high concen%rations. A drop in yield of 23% is observed for a :solution 0.2 M in 1) which may be compared with a :25% drop found by Burton and Patrick2 for a (0.25 M m-terphenyl solution. The effect of iodine sappears to be the same in lowering the H2and C2 .yields. It has previously been shown in the case of cyclohexane that for dilute solutions (
