COMMUNICATIONS TO THE EDITOR
4161
of the justification of the assumptions inherent in eq 1 and eq 2. Acknowledgment. It is a pleasure to acknowledge the valuable correspondence with Professor H. S. Johnston of the University of California, Berkeley, Calif. LABORATORIES DIVISION AEROSPACECORPORATION EL SEGUNDO, CaLIFoRNIA 90245
S. W. MAYER
RECEIVED AUGUST25, 1967
t i L
!
235
I
I
26 0
255
I - & 310
WAVELENGTH IN MILLIMICRONS
Radiolytic Products of Liquid Ammonia'
Sir: Radiolysis of liquid ammonia results in the A recent publicaformation of Hz, N2, and N2H4.'-' tion reports that HN3 is also a radiolytic product.' In this communication, we present the results of experiments8 showing that a t least two other products, one of which is "3, are formed in the radiolysis of liquid ammonia. Samples of liquid ammonia that had been purified by storage over sodium, followed by trap-to-trap distillation, were irradiated at 10" with Co60 y-rays for total doses of 1 X lo4 to 1.5 X 108 rads. The yields of H2, Nz, and N2H4 were measured. The amount of excess hydrogen, calculated from the material balance equation H2,excess
=
Hz,obsd - NZH4,obsd - 3N2,obsd
was plotted as a function of dose. Two distinct dose regions, (1) I 3 0 X lo3 rads, where G(H2,excess) = 0.51 f 0.03, and (2) >50 X lo3 rads, where G(H2,excess) = 0.14 0.03, were found where there was a lack of material balance. Thus either additional products with a N2:HZ ratio > 1:2 were present or impurities were an important influence in the radiolysis. No evidence for any impurity was found. When alkaline aqueous solutions of ammonia, which had been irradiated to doses 5 3 0 X lo3 rads, were examined spectroscopically, two broad absorption bands centered at 285 and 243 mp were observed (Figure 1, curve 111). On acidifying, these bands disappeared and a more intense band at 230 mp was observed (Figure 1, curve IV). These absorption spectra were similar to that of a control solution of tetramethyl tetrazene (curves I and 11) and to that previously observed for alkyl tetra~enes.9~'~These results, together with the observation that on increasing the dose these bands disappear with the formation of nitrogen, suggest that the unknown species contains a K=N group. Possible compounds which may be present are , (N3H3), or tetrazene (X4H4). diazene (SzHz)triazene
Figure 1. Typical ultraviolet spectra of aqueous solution of liquid ammonia irradiated to doses 5 3 0 X 103 rads: I, solution of tetramethyl tetrazene, p H 2.8; 11, solution of tetramethyl tetrazene, p H 11.8; 111, aqueous solution of irradiated ammonia, p H 11.8; and IV, aqueous solution of irradiated ammonia, p H 2.8.
Typical ultraviolet absorption spectra of aqueous solutions of ammonia, which had been irradiated to doses >50 X lo3 rads, are shown in Figure 2. In basic and neutral solution (curve 111), absorption spectra show little structure, while in acid solution (curve IV), there is a broad absorption band a t 260 mp. This behavior is similar to that of control samples of NaN3 (Figure 2, curves I and 11). The presence of N3- was confirmed by measuring the infrared spectra of (1) an acidified aqueous solution of irradiated NHs and (2) of a KBr pellet prepared from t.his solution (Table I). Absorption bands characteristic of azide were observed. A further experiment was carried out in which helium was bubbled through an acidified aqueous solution of irradiated liquid ammonia and passed through a liquid nitrogen trap. The trap was allowed to warm up and the resulting vapor expanded (1) This work was performed under the auspices of the U. S. Atomic Energy Commission. (2) D. Cleaver, E. Collinson, and F. S. Dainton, Trans. Faraday SOC.,56, 1640 (1960). (3) L. Kolditz and U. Prosch, Z . Physik. Chem., 208, 108 (1962). (4) J. R. Puig and E. Sehwars. "Industrial Uses of Large Radiation Sources," Vol. I, International Atomic Energy Agency, Vienna, 1963. (5) F. S. Dainton, T. Skarski, D. Smithies, and E. Wemamowski, Trans. Faraday SOC.,60, 1068 (1964). (6) D. Schischkoff and D. Schulte-Frohlinde, 2. Phgsik. Chem., 44, 112 (1965). (7) J. Belloni, J . Chim. Phys., 9, 1281 (1966). (8) J. W. Sutherland and H. Kramer, Annual Reports, Nuclear Engineering Department, Brookhaven National Laboratory, Upton, Long Island, N. Y.: BNL 900 (5-67). p 83, 1964; BNL 954 (5-681, p 88, 1965; BNL 994 (AS-20), p 61, 1966. (9) T. M.Bins and N. R. McBride, Anal. Chem., 31, 1382 (1959). (10) N. R. McBride and €1. W. Kruse, J . Am. Chem. SOC.,79, 572 (1957).
Volume 71,Number 19 November 1967
COMMUNICATIONS TO THE EDITOR
4162
~
~~~
Table I : Infrared Data on Unknown “Species” Found at High Doses“
:I w z 0
KB r pellet of sample, cm-1
NaNa control, cm-1
Lit. assignmen+
I-
3490 2107 1600 1267 730 655 637
3490 2130 1600 1262 740 658 64 1
3455 2128,2189 1567 1267 718 644 628
k-
Acidified aqueous solution, cm-1
Control sample of HNs, om-’
Lit. assignment,brc cm-1
3333 3333 3310d 2105 2105 2105 1600 1600 ... a Perkin-Elmer Model 221 spectrophotometer. b H. A. Papazian, J. Chem. Phys., 34, 1614 (1961). c P. Gray and T. C. Waddington, Trans. Faraday SOC.,53,901 (1957). A. M. Buswell, et al., J. Am. Chem. SOC.,61, 2809 (1939).
into a 1-m infrared gas cell. Absorption bands characteristic of HN3 were observed. From these experiments, it is concluded that HNa
The J O U T of ~ Physical Chemiatly
a !z
5z a
235
I
1
I
260
285
310
,-I 335
WAVELENGTH IN MILLIMICRONS
Figure 2. Typical ultraviolet spectra of aqueous solution of liquid ammonia irradiated to doses 2 5 0 X 10a rads: I, solution of KNa, p H 2.8; 11, solution of KN,, p H 11.8; 111, aqueous solution of irradiated ammonia, p H 2.8; IV, aqueous solution of irradiated ammonia, p H 11.8.
is a product in the radiolysis of liquid ammonia at doses >40 X lo3 rads, and a t doses
