1402
COMMUNICATIONS TO THE EDITOR
Production of Nz(A3Z) and CO(a37r) by Hg('P1) Photosensitization ; Pressure Dependence
of 2537-A Emission'
Sir: The pressure dependence of emission at 2537 8 when NZ or CO undergo Hg('P1) photosensitization provides compelling evidence for the excitation of these species to their respective A32 and a37r states. Excitation of Hg to its 3P1state by energy transfer from Nz(A32) has been proposed2 to account for the observed 2537-8 emission when Hg vapor is exposed to active nitrogen; kinetic studies3 have confirmed this proposal. Emission at 2537 8 from the Hg(lP1) photosensitization of Nz or CO has been detected4 spectrographically, and the possibility of the generation of Nz(A3Z)and CO(a37r) by energy transfer from Hg(lP1) has been inferred from this observation. The observed chemistry of CO under Hg('P1) photosensitization has been interpreted5 in terms of CO(a37r). We have studied the pressure dependence of 2537-8 emission under the conditions of both Hg('P1) and Hg(3P1)photosensitization. A 2-in. diameter, flat-spiral, low-pressure mercury resonance lamp (Hanovia Corpb) fabricated of Suprasil quartz provided 2537- and 1849-A radiation. Isolation of X 1849 8 was effected by using an LiF window which was freshly irradiated with 2Mrad doses of 6oCoy rays. A Corning 7910 filter was used to isolate the 2537-8 line. Emission at 2537 8 was measured at right angles to the incident beam by means of a Jarrell-Ash 0.5-m Ebert monochromator, EM1 6255 B photomultiplier, and Tektronix 535 A oscil!dscope with photographic recording; The quenching by N2 or CO of X 2537-A fluorescence produced by irradiation at this wavelength obeyed the Stern-Volmer relationship over the pressure range to 700 torr, From the ratio of the slopes of these plots, the ratio of quenching rate constants, ~ Q ~ O / ~ Q= "23, was calculated, in excellent agreement with the ratio of the accepted values of >hese constants.6 The observed emission of 1 2537 A from incident 1849 8 in the presence of Nz7or CO, corrected for the measured quenching of X 2537 8 under identical conditions, is analyzed below. The analogous emission at 2537 8 in the presence of Ne or He was negligible. Equation A is readily derived from the mechanism8 Hg('S0) Hg(lPd
+ hv(1849 8) +Hg('P1)
+ Nz(XIZ)
--t
Hg('P1) -+- Hg('So) Nz(A3Z)
+ Hg('S0)
Hg(W
-+N2(X1Z)
Hg(3Pl) +Hg('S0)
(W
(kf1849)
+ Hg(W
+ hv(2537 8)
I
I
0.1
I
0.2
I
I 0.3
0.4
I / P , TORR-~
Figure 1. Plot of 2537-A emission data in the form of eq A: 0, Nz; a, CO.
An analogous set of equations can be written for CO. Agreement of the data for Nz and CO with eq A is demonstrated in Figure 1. The value of slope/intercept of these plots, kf'849/k1, is 27 for Nz and 13 for CO. Although the significance of kf1849is complicated by imprisonment of radiation, it can be concluded that the energy-transfer process represented by kl is of similar efficiency for Nzand CO. (1) Supported by the Air Force Office of Scientific Research under Contracts AF-AFOSR-765-65 and 765-67. (2) W. R . Brennen and G. B. Kistiakowsky, J . Chem. Phys., 44, 2695 (1966). (3) R. A. Young and G . A. St. John, ibid., in press. (4) T. A. Gover and H . G. Bryant, J. Phys. Chem., 70, 2070 (1966). (5) G. Liuti, S. Dondes, and P. Harteck, J. Chem. Phys., 44, 4051 (1966). (6) J. G. Calvert and J. N. Pitts, Jr., "Photochemistry," John Wiley and Sons, Inc., New York, N. Y., 1966, p 74. (7) We have also found that quenching of Hg(lP1) fluorescence by NZfollows the Stern-Volmer relationship. (8) Radiative and wall decay of Nz(A32) is assumed to be negligible over the range of conditions.
DEPARTMENT OF CHEMISTRY BOSTON UNIVERSITY BOSTON, MASSACHUSETTS 02215
A. GRANZOW M. 2.HOFFMAN N. N. LICHTIN 5.K. WASON
RECEIVED JANUARY 23, 1968
Reactions of Tetranitromethane with
+ Nz(A32)
+ hv(1849 A)
I/ 12637 , ARBITRARY UNITS
(kz)
(kt25a7)
Hydroxide Ion and Nitrite Ion
Sir: For some time we have been studying the reactions of tetranitromethane (TNM) with hydroxide ion and nitrite ion. The quantitative conversion of TNM to nitroform with nitrite ion has already been reported.' (1) D. J. Glover, J. C. Dacons, D . V. Sickman, M. E. Hill, and M. J. Kamlet, U. 8. Patent 3,125,606 (March 17, 1964).
The Journal of Physical Chemistry
COMMUNICATIONS TO THE EDITOR
1403
We have obtained kinetic data for the reaction of T N M with hydroxide ion and nitrite ion which will be reported in a later communication. During this study in dioxane-water mixtures (the solvent varied from water to dioxane-water mixtures), it became evident that with insufficiently purified dioxane, an immediate reaction was occurring which could be explained by reaction with peroxides present in the dioxane. By adding a known amount of hydrogen peroxide (1.5 X M final) an immediate reaction occurred producing equivalent quantities of nitroform ion (1.5 X M ) and nitrite ion (1.6 X M ) . The solution was initially 9.2 X M in T N M and 0.1 M in potassium bicarbonate. In a recent report in this journal,2 it was stated that T N M was found not to react with either nitrite or peroxide alone or with both together at pH 5 or above. The results with nitrite ion are contrary with the findings in this laboratory as reported in ref 1. It is not at all obvious why Bielski and Allen2 did not observe the reactions with peroxide. Their experiments involved hydrogen peroxide of the order of 10" M and M . As shown above, nitroT N M of the order of form would be produced equivalent to loF6M a t a pH corresponding to that with bicarbonate ion. The actual rate constant found by Hoffsommer3 for the reaction with hydroperoxide ion was 1.44 X 10* l./mole sec, in water. The results of the kinetic study of T N M with base in dioxane are illustrated by the data in Figure 1. That the autocatalytic reaction is due to nitrite ion is clearly shown. Nitrite ion was added initially and the slow reaction is absent. When nitrite ion was not added, the other products were nitrate ion equivalent to the nitroform produced and nitrite ion equivalent to four times the TNM not going to nitroform. That this latter reaction also gives rise to carbonate ion was shown by S ~ h m i d t . ~Carbonate ion and nitrate ion in the
present study were shown not to affect the reaction, The rate constant for the reaction of TNM with nitrite ion was found by interpolation to 0.46 l./molehr at 24" and explains why Bielski and Allen2 observed no reaction with nitrite ion. With nitrite ion 10-6 M and T N M lova M , a yield of nitroform of 5 x 10-9 M would be expected which could not be detected under their conditions. I n our study, when the base concentration was sufficiently low and the nitrite ion sufficiently high, only nitroform, nitrate ion, and nitrite ion were produced, confirming the catalytic nature of nitrite ion. The reactions studied in our kinetic investigation were
+ 6OH- + f 4NOz- + 3Hz0 C(NO2)4 + 20H- +C(NOz)3- + NO,- + HzO c(NOz)4
c03'-
C(NOz)4 Nz04
+ NOz-+
+ 20H-
c(N02)3-
+ NOz-
+ Nz04
+ NO3- + H2O
(1) (2)
(3)
(4) The product N204,although not identified, explains the results most satisfactorily. (2) B. H. J. Bielski and A. 0. Allen, J. Phgs. Chem., 71,4544 (1967). (3)A detailed kinetic study of the reaction of T N M with various peroxides has been reported by J. C . Hoffsommer, Doctoral Thesis, George Washington University, 1964. The results of this study are also planned for a future communication. (4) E. Schmidt, Ber., 52B, 400 (1919).
u. s. NAVALORDNANCE LABOR.4TORY
DONALD J. GLOVER CHEMISTRY RESEARCH DEPARTMENT ADVANCED CHEMISTRY DIVISION WHITEOAK, SILVER SPRING,MARYLAND RECEIVED FEBRUARY 5, 1968
Homogeneous Periodic Reactions
Sir: Two reactions are known which oscillate and which have been reported to take place in a homogeneous phase. One is the reaction between hydrogen peroxide and periodate in acid solution,' and the other is the series of cool flames observed in hydrocarbon oxidations.2 The reason for the oscillatory behavior of cool flames appears to be that one of the rate-determining reactions has a negative temperature coefficient,* and as the temperature rises, the reaction dies out, restarting again when the system cools. We have performed experiments4 at 60" on the reac-
0.04
0.03
M 0.02
0.01
0
4
8
12
16
20
24
28
32
36
40
TIME (MINUTES)
Figure 1. Formation of nitroform from TNM by reaction with hydroxide in dioxane-water.
44
(1) W. C. Bray, J. Amer. Chem. Soc., 43, 1262 (1921). (2) B. Lewis and G. von Elbe, "Combustion, Flames and Explosions of Gases," 2nd ed, Aoademio Press Inc., New York, N. Y . , 1961. (3) J. H. Knox in "Photochemistry and Reaction Kinetics," P. G. Ashmore, F. S. Dainton, and T. M. Sugden, Ed., Cambridge University Press, Cambridge, England, 1967. (4) We are indebted to Mr. R. I. McLean for assistance with these experiments and to Mr. V. A. LoDato for helpful discussions. Volume 72, Number 4
April 1968
