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Chem. Phys., 82, 101 (1968); (c) R. A. Saunders, J. T. Larkins, and F. E. Saaifeld, Int. J. Mass Spectrom. Ion Phys., 3, 203 (1969); (d) F. J. Preston, M. Tsuchiya, and H. J. Svac, ibid., 3, 323 (1969). (6) (a) G. Mauclaire and R. Marx, J. Chim. Phys., 65, 213 (1968); (b) R. Marx and 0. Mauclaire, Adv. Chem. Phys., 82,212 (1968); (c) R. Marx, G. MauClaire, and M. Wallart, J. Chlm. Phys., 68, 1980 (1971). (7) (a) G. Glocker and L. B. Thomas, J. Am. Chem. SOC.,57, 2352 (1935); (b) J. E. Manton and A. W. Tickner, Can. J. Chem.,38, 858 (1960); (c) B. Gltton, Thesis, Paris, 1967; (d) J. Blais, B. Gitton, and M. Cottin, lnt. J. Radiat. Phys. Chem., 4, 369 (1972); (e) C. D. Flnney, Thesis, Kansas State University, 1970; (f) C. D. Finney and H. C. Moser, J. Phys. Chem., 75,2405 (1971); (9) J. Danon, R. Derai, and J. Mllhaud, Adv. Radiat. Res. Phys. Chem., 1, 159 (1973); (h) R. Derai, Thesis, Paris-Sud University, Orsay, 1975. (8)J. W. Raymonda and W. T. Simpson, J. Chem. Phys., 47,430 (1967). (9) R. Marx, G. Mauclaire, and M. Wallart, unpublished results. (IO) F. H. Fieid and F. W. Lampe, J. Am. Chem. SOC.,80, 5587 (1958). (1 1) F. W. Lampe and F. H. Field, J. Am. Chem. SOC.,81, 3238 (1959). (12) S.G. Lias and P. Ausioos, J. Chem. Phys., 43, 2748 (1965). (13) T. Miyazaki and S. Shida, Bull. Chem. SOC.Jpn., 39, 2344 (1966). (14) L. W. Sieck, S. K. Searles, and P. Ausloos, J. Res. Natl. Bur. Stand., Sect. A, 75, 147 (1971). (15) V. I. Ochkur, Sov. Phys. JETP, 18, 503 (1964). (16) J. H. Johnson, R. H. Knife, and A. S. Gordon, Can.,/.Chem.,48,3604(1970), (17) R. E. Rebbert, S.G. Lias, and P. Ausloos, J. Pbotochem., 4, 121 (1975).
(18) G. D. Flesh and H. J. Svec, J. Chem. SOC.,Faraday Trans. 2, 69, 1187 (1973). (19) R. Derai and J. Danon, to be submltted for pubilcatlon. (20) R. Deral and J. Danon, Chem. Phys., in press. (21) P. Nectoux, R. Deral, and J. Danon, to be submitted for publication. (22) R . E. Rebbert and P. Ausloos, J. Res. Natl. Bur. Stand., Sect. A, 76, 329 (1972). (23) M. S. B. Munson, J. Am. Chem. SOC.,90, 63 (1968). (24) P. Ausloos and S.G. Lias, J. Am. Chem. Soc., 92, 5037 (1970). (25) P. Ausloos, private communication. (26) S. G. Lias, R. E. Rebbert, and P. J. Ausloos, J. Am. Chem. SOC.,94, 2080 (1972). (27) G. J. Collin, Can. J. Chem., 52, 2341 (1974). (28) (a) R. P. Borkowski and P. Ausloos, J. Chem. Phys., 40, 1128 (1964); (b) S . G. Lias, R. E. Rebbert, and P. Ausloos, J. Am. Chem. Soc., 92, 6430 (1970). (29) M. J. Giblan and R. C. Corley, Chem. Rev., 73, 441 (1973). (30) P. D. Pacey, Can. J. Chem., 51, 2415 (1973). (31) W. E. Jones, S. D. MacKnight, and L. Teng, Chem. Rev., 73, 407 (1973). (32) P. Ausloos and E. W. R. Steacie, Can. J. Chem., 33, 47 (1955). (33) This decrease results from an increase in the absorption probability of parent molecules as the neopentane pressure increases. (34) F. W. Lampe, J. Phys. Chem., 61, 1015 (1957). (35) Subscripts refer to the reactlon by which the product Is formed.
Oxygen Radiolysis by Modulated Molecular Beam Mass Spectrometry Valerie R. Kruger and Donald R. Olander" Materials and Molecular Research Division of the Lawrence Berkeley Laboratory and the Department of Nuclear Engineering, University of California, Berkeley, California 94720 (Received August 1 1, 1975; Revised Manuscript Received February 17, 1976) Publication costs assisted by Lawrence Berkeley Laboratory
An experimental system for on-line mass spectrometric analysis of gas phase radiolysis systems was developed. Oxygen in a fast flow reaction tube was irradiated with 1MeV protons and subsequently sampled with a molecular beam source. Analysis of the modulated molecular beam with a quadrupole mass spectrometer provided the concentrations of 0,02, and O3 as functions of reaction time, dose rate, and system pressure. Observed ozone levels were anomalously high compared to the predictions of existing chemical models, with apparent g values considerably above theoretical maximum values. Agreement of theory with the data was improved by postulating an excited state of 0 2 as a direct precursor to ozone.
I. Introduction Ideally, a complete description of the interaction of highenergy radiation with a gas should identify all chemical species produced, determine the production efficiency for each, and consider the kinetics of all subsequent chemical reactions which ultimately lead to stable products. Oxygen radiolysis, in which the sole stable product is ozone, is interesting for several reasons. First, the action of high-energy protons on low pressure oxygen, which is the subject of the present study, simulates the effect of solar flare protons on the upper atmosphere. Second, the process has potential application in chemonuclear ozone production.lS2 Third, oxygen radiolysis is especially simple for experiments utilizing on-line mass spectrometry, since only three species, 0,02,and 0 3 , are observable in the mass spectrum. Finally, the rate constants of many of the homogeneous reactions involved in the overall process are well known, so that the unknown aspects of the radiolysis can be singled out for study. Although oxygen radiolysis has been studied previously, the experiment described here differs in several respects from The Journal of Physlcal Chemistry, Vol. 80, No. 15, 1976
earlier experiment^.^-^ In the present system, atomic oxygen is measured in addition to ozone. Both products are observed on-line simultaneous with irradiation. The chemical reactions take place concurrent with irradiation rather than afterwards, as in pulse radiolysis. 11. Experimental Description
The quantities measured are the concentrations of atomic oxygen and ozone, as functions of gas pressure, gas flow rate, and proton beam intensity. The apparatus shown in Figure 1 can be divided broadly into three systems: (A) equipment for production and measurement of the proton beam; (B) the reaction tube and the flow system; (C) mass spectrometer for identification and quantitative measurement of the radiolysis products. A. Production and Measurement of the Proton Beam. The primary proton beam is produced by a 1-MeV Van de Graaff accelerator. The protons are deflected into the reaction tube by a bending magnet, which produces a monoenergetic beam. One of the major problems in this work was to devise a
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Oxygen Radiolysis by Protons To Chopper Motor
m Two- Pen Sirip-Chart Recorder
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I
I on Pump
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Figure 1. Schematic of the radiolysis apparatus.
method of introducing the proton beam into the reaction tube, where the gas pressure is several Torr, from the accelerator tube where the pressure is Torr. Thin windows of aluminum, beryllium, carbon, and formvar were tested but these failed quickly because of localized heating by the proton beam and attack of the hot spot by the reactant gas. Eventually, the differential pumping system shown in the lower left-hand corner of Figure 1was developed. Two channels (or collimators) 2.5 mm in diameter and 10 cm long separate the reaction tube from the accelerator. Each collimator is followed by a vacuum pump. The basic idea was to sufficiently restrict the flow of the randomly moving reactant gas into the accelerator so as not t o exceed allowable pressures there yet at the same time not lose too much of the incident proton beam on the collimators. The collimator system which was devised satisfies the following criteria: (1)the pressure rise in the accelerator tube during the operation with 10 Torr gas pressure in the reaction tube is approximately Torr; (2) the fraction of the total gas flow in the reaction tube which is pumped off by the collimator system is small (
