W. N. PATRICK AND MILTONBURTON
2626
Vol. 76
by S z w a r P as -2.6 e.v. in rather good agreement with a value of 2.9 e.v. estimated from the 4.65 They specifically note an inability to detect free e.v. value of the H-NHz bond. Neglecting considNH in the electric discharge through ammonia even erations of possible difference in cross-sections for a t low pressure. Unfortunately, there does not the electronic interactions and assuming, as before, appear to be any direct evidence of reaction or ab- that the average electron temperature is about 1.4 sence of reaction in the gas phase between N H radi- e.v., i t follows that the probability of production of NzH4* is a t the most about 5 times that of attaincals, i.e. ment of path I. Thus, preferential excitation of S H + S I 3 ----f h-2 + Hy (8) N2H4 would not appear to be the limitation responsor between NH radical and some other molecule ible for the relatively low concentration of hydrasuch as NH3or NzH4. Reaction 6 has a formal sim- zine (e.g., -0.04 mole per cent. in Table I, run 56) M(?) obtain in this work, so that reaction 4 rather than HZ --+ CHI, which appears to reaction 3 would appear to be the major restriction on ilarity to CH2 be rather well e s t a b l i ~ h e d . ~ ~ ~ ~ * yield and steady-state concentration of hydrazine. Reactions between NH and NH2 radicals are This conclusion is contrary to the view of O ~ c h i . ~ ~ ruled out by the fact that the yields of NPand N2H4 4.6 Reaction in the Negative Glow.-Whether (the products of the presumed reactions 2 and 5 or production of inappreciable quantities of hydrazine 8) are not interdependent (cf. section 4.1.7). in the negative glow is due to its rapid destruction or The catalytic effect of platinum walls on hydra- to its substantial lack of formation in thisregion is not zine formation suggests the importance of a reaction known. The average energy near the cathode edge which can interrupt the back reaction, 2 or 4, e.g., is probably higher, while that near the anode edge lower, than that existing in the positive column.6d 1\1 H + H -+HZ Evidence has been presented that at high flow rates or W some hydrazine does escape from this region. The effect of platinum walls is explained most simThe data in A.D.I. Tables 2 to 4 indicate a maxiply by increase in the rate of reaction 9 and conse- mum energy efficiency for nitrogen production in quent decrease in rate of reaction 4. the negative glow between 2 and 3 mm. pressure 4.5 Hydrazine Decomposition.-Hydrazine is with a value approximately equal to that in the posrapidly destroyed in the discharge and nitrogen is itive column a t high pressures. The paucity of not formed in this process (section 4.1.3). Steady- data available on the reaction and on the electron state concentrations were established a t values energy distribution in this r e g i ~ n ~ ~forbid s ~ s g discusless than 0.1 mole per cent. in the platinum-coated sion of mechanism. The situation is further comtube. The lowest excited state of hydrazine is plicated by the possibility that reactions occur in probably triplet and the lowest significant excited the Faraday dark space.4c state probably corresponds to the dissociation en(25) Cf.M.Szwarc, Chem. Reus., 47, 75 (1950). If a low NH bond ergy of the H~N-NHzbond. This figure is given dissociation energy is assumed for NHs (cf. footnote 14) the agreement IV
4NH
+ NHaN3
(7)
+
.r
(24) C. E. H. Bawn and J. Milstead, T r a n s . Faraday Soc., 3 6 , 889
is better.
NOTREDAME,INDIANA
(1939).
[CONTRIBUTION FROM THE
DEPARTMENT O F CHEMISTRY, UNIVERSITY
OF
NOTREDAME]
Polymer Production in Radiolysis of Benzene1v2 BY W. N. PATRICK AND -MILTONBURTON RECEIVED JANUARY 4, 1954 Irradiation of liquid benzene with 1.5 hlv. electrons gives polymer as a non-volatile product with a 100 e.v. yield G(CeH8 + polymer) = 0.75 independent of intensity and total energy input. Average molecular weight increases non-linearly with At the same time G(doub1e bond formation) decreases linearly energy input; the maximum value observed was -530. with input independent of intensity. I n explanation of the results it is suggested that a fixed fraction of the primarily excited benzene molecules are excited to a particular energy level and then react to give polymer formation.
1. Introduction Polymer is produced in electron-bombardment radiolysis of benzene with a 100 e.v. yield of benzene molecules converted to polymer, ;.e., G(CeH8 + polymer), previously given as 0.76.3 Little, however, has been published about its production or its (1) A contribution from the Radiation Project operated by the University of Notre Dame and supported in part by the Atomic Energy Commission under Contract AT(ll-1)-38. ( 2 ) Abstract from a thesis presented to the Department of Chemistry of the University of Notre Dame by W. N. Patrick in partial fulfillment of requirements for the degree of Doctor of Philosophy. (3) J. P. Manion and M. Burton, J. P h y s . Chcm., 66, 560 (1952).
nature. Such information, useful perhaps for elucidation of the mechanism of radiolysis of benzene and for clarification of some details of behavior of benzene mixtures, is presented in this report. 2.
Experimental
The benzene used in this work was a portion of an exceptionally high-purity sample' previously employed in synthesis of benzene-&. Techniques of irradiation by 1.5 Mv. electrons are largely those described in an earlier paper.' However, for determination of polymer, the irradiation cells were necessarily modified by extension of the (4)
W.N. Patrick and M. Burton, ibid., 68, 424 (1954).
POLYMER PRODUCTION IN RADIOLYSIS OF BENZENE
May20, 1954
-
reservoir with a length of 8 mm. tubing. Although the 4.8 ml., the irradiated volume total volume of liquid was was
