1337
Communicaticm to the Editor
r
e,
B. Smaller, E. C. Avery, and ,I. R. Remko, J. Chem. Phys., 55, 2414 (1971). See for review, L. Kevan in "Radiation Chemistry of Aqueous Systems," G . Stein, Ed., Weizman Science Press of israei, Jerusalem, 1968, p21. Far the experimental setup see, H. Shiraishi, H. Kadoi, K. Hasegawa, Y . Tabata, and K. Oshima, Bull. Chem. Soc. Jap., 47, 1400 (1974). K. Kume, J. Phys. SOC.Jap., 15, 1493 (1960). ATthe hi her temperature, OH and SO4- radicals which accumulate at -196 decay so rapidly that they give hardly any spectra. There remain some unknown species whose G value is very small. The situation is similar for HCI solution. In fact, the intensity of H atom signal changed very little during the course of irradiation P. W. Atkins, R. C. Gurd, K. A. Mclauchlan, and A. F . Simpson, Chem. Phys. Lett., 8, 55 (1971). Department of Polymer Technology, The Royal Institute of Technology, Stockholm, Sweden, an leave from the University of Tokyo. Address correspondence to the Nuclear Research Laboratory, Faculty of Engineering, University of Tokyo 7-3-!, Hongo, Bunkyo-ku, Tokyo, Japan,
>
"!-
Dose Rate, Mradlmin
.(i
9
-= 8
4
12
16
20
Dose'Rate, Mradlmln
0
-"-, \\
I-
m-
Department of Nuclear Engineering University of Tokyo Tokyo, Japan
Hirotsugu Shiraishig Hajime Kadoi Vosuke Katsumura Yoneho Tabata* io Keichi Oshima Received October 29, 1973; Revised Manuscript Received Apnl29, 1974
' '\
\ '\
\
', A\
r a t e dependence of H atom signals in
(a) 0.5 M
H2S04solution at --77', (b) 1 M HCI solution at -78': field line; 0, low-field line.
0 , high-
Figure
I. Dose
perature regiton (Figure 1). Neither the H F line, nor t,he L F line is proportional to the dose rate in contrast to the observation by :Fessenden, et aL2 Still more important is the difference in dependence of the LF and HF line intensity upon the change of dose rate. In liquid-phase experiments, both iincs are reported always to appear in about the same intensjty."3 Increasing the dose rate results in a decrease of the life time of H atoms due to the increase of their concentration.. Tlnus, the weakness of the LF line relative to the :HF line at low dose rates is attributable to the relaxation process that effects significantly when the life time is long. On the other hand, the difference a t the higher dose rate., or, more explicitly, the fact that the LF h e far exceeds .the HF line in the case of 1 M hydrochloric acid solution a t igh dose rates (Figure l b ) has an important implication to the theory of the phenomenon. This cannot be ascribed to a difference between the reaction schemes in the d i d and liquid state, and must be due to the polarization process itself. Interpreted from the standpoint of the radical pair theory,l this phenomenon cannot be explained only by the mixing of singlet S and triplet To, since -1; predicts equal polarization for both lines. As was proposed by Atkins, et U L . , ~ in the quite different case with radicals that have excited triplet precursors, the mechanism of mixing of triplet T-1 with S must be contributing :it least to a comparable order, though it is difficult to explain at the present stage why the latter mechanism sh.ould be emphasized in the present experiment. :Further experiinents and analysis are necessary to clarify the polarization mechanism, and we think this system is a good example for such study. References and PlJoltes (1) See for review, P. W. Atkins and K. A. Mciauchlan in "Chemically Induced Magnetic Po!arization," A . R. Lepley and G. L. Cioss, Ed., Wilsy, New York, N. Y . , 1973, p 42. (2) (a) P. Neta, R . \N. Fessenden, and R. H. Schuler, J. Phys. Chem., 75, 1654 (1971) (b) N. 12, Verma and R. W, Fessenden, J. Chem. Phys., 58, 2501 11973).
Reaction of the Nitrate Radical with Acetaldehyde and Propylene Publication costs assisted by the f o r d Motor Company
Sir: Acetaldehyde is known to react rapidly1 with a mixture of 0 s and NO2 but rather slowly2 with O3 or NO2 alone. NzO5 and NO3 are produced in the 03-NO2 system by the reaction^^,^ 0,
+ NO,
NO3
+ NO,
-
NO,
+ 0,
k , = 4.4 x IO-''
cm3 molecule-' sec-'
(1)
N,O, K = k-.Jh2 = 0.80
X
10" molecule/cm3
(2)
It has also been reported5 that a mixture of N205 and CH3CHO gives a high yield of peroxyacetylnitrate (PAN). Thus either Nz05 or NO3 is reacting with acetaldehyde. Stephens1 has observed that the PAN yield in the O3 NOz -t- CH3CHO system falls off sharply when [ N 0 ~ ] / [ 0 3 ] 9 2. Since reactions 1 and 2 require a stoichiometry of two molecules NOpper molecule of 0 3 , excess NO2 reduces the NO3 concentration by shifting reaction 2 toward Nz05. Hanst6 has analyzed these data and calculated the NO3 concentration using reactions 1 and 2 . From the linear relation between PAN yields and NO3 concentrations, he concludes NO3 is involved in PAN formation. As suggested by various author^,^ a plausible mechanism for PAN formation is given by NO, + CH,CHO --+HNO, + CW,CO~ (3)
+
CH,CO.
+ 0, CH,COOO, + NO, PAN
CH,C000*
+
-
(4) (5)
In view of the potential role of these reactions in photochemical smog formation, the kinetics and mechanism of the Nz05 + CH3CHO system have been studied in some detail. Since the reaction of propylene with N02-03 mixtures also yields PAN as a product, the N20&3& system has also been investigated. The concentrations of reactants and products were determined using a 40-m path length infrared cell. A deThe Journal of Physical Chemistry, Vol. 78, No. 73, ?974
Communicationsto the Editor
133
._-
CI
5
IO 15 TIME [ M I N U T E S ]
20
Figure
1. Tirne/concentration plot of N 2 0 5 as a function of CH3CHO and NOn. Solid lines are calculated, points are experimental data [ N 2 0 ~ ] 0 = 3.1 mTorr: curve A , N 2 0 5 alone; curve 5, [CH&HO]o = 28 mTorr, [NO210 = 4.6 mTorr; curve C, [CH:jCHO]o = 28 rnTorr, [NO210 = 2.3 mTorr; curve D, [CH:iCHQ]o = 14 mTorr, [NO& = 0.57 mTorr (calculated, see
text).
tailed description of this apparatus has been given previously.8 PAN was analyzed both by infrared absorption and by electrm capture gas chromatography. Most experiments were carried out using 400 Torr of 0 2 and 350 Torr of argon as diluent, at 300°K. Kinetic data were obtained by measuring the rate of N2Q5 decay in the presence of various concentrations of CH:,CHO and NQZ. The results are shown in Figure 1. The points are experimental data, while the lines are calculated basad on reactions 2-6 as explained later. Curve D in this figure shows that the decay of N205 increases significantiy over the background rate (curve A) when acetaldehyde is added. The first-order decay of N2O5 was found to be proportional to CH3CHO concentration. The addition of NO2 reduces the rate of reaction as shown by curves I3 and 6. The addition of ozone (not shown) increases the decay rate of NzO5. This is consistent with the occurrence of reaction 3 since the addition of 0 3 increases the NO3 concentration. Several experiments carried out a t a low partial pressure of oxygen (
