J. Phys. Chem. 1980, 84, 1797-1801
TABLE V: Dipole-Moment Derivatives of Acetylene-d and v s-v4 Transition 'Moment of Acetylene-daa -derivative from 6 p from 6 p mean (azpil/aa2)), -2.16 -2.09 -2.12 D/rad2 -1.66 1.86
-1.7 3 1.813
( azpzl a a (aZpz/ap')e
(a ' p Z / a 01 a P )e v 5-v4
calcd
Transition Moment of C,D, 0.0388
0.0372
;Zind
0.0260
0.0244
;$I1
0.0405
0.0389
anh
obsd (apLl/aa), =
Reference 22.
-1.70 D/rad2 1.89 D/radz 0.10 D/radz 0.0380 D 0.0128 D 0.0252 D -0.0017 D 0.0397 D 0.0358 ( 2 0 ) Db
1.0549 ?: 0.0569 D/rad (ref 1 7 ) is assumed.
and 6pgII. As listed in Table V, two values thus obtained differ only by 0.07 U/rad2. As a test of our model, we have applied our results to the u5-u4 transition rnoment of C2D2which Lafferty et a1." determined from Stark effects of microwave transitions. The transition moment pvib is given by 2nd (39) &it, = &ibmh + Pvib where x /.bvibanh = -(l/8n)((w3 + w4 - 0 5 ) - l + (w3 - w4 +
The vibrational transition moment and its various components which were calculated by using our results on the CzHD molecule are listed in Table V. The agreement with the experimental value is satisfactory. It is also noted that &,iblI gives an overwhelmingly large contribution to p ~ in b comparison with Pvibl. Acknowledgment. The calculation made in the present work was carried out at the Computer Centers of the Institute for Molecular Science and Kyushu University.
References and Notes (1) (2) (3) (4) (5) (6) (7) (8)
(9) (10) (11) (12)
( h / ~ ~ 3 ) ~ ' ~ ( d ~ / d Q (40) 3 ) e ~ ~ ~(13) ~
(41) It may also be given as the sum of p v i t and / . ~ ~which ~2~, depend respectively upon the first and second derivatives with respect to curvilinear symmetry coordinates: (42) &ib = k i bI + c Lvib .II where PviJ = [-(1/8n){(% + w4 - w5) -l (w3 - w4 + wg)-1 ) x ( h / ~ ~ ~ ) ~ / ~ (h/87r2c) q 5 ~ ~( w ~ 4L0 :5 ~) - ~ 1 / z(dp/dS3), L~5] (43) &ibZnd
=
(14)
(h/8n2~)(~4~g)-1'2(d2~/dQ4xdQ5x)e
(15) (16) (17) (18) (19)
+
+
1797
(23)
Institute for Molecular Science Graduate Student for 1978-79. J. S. Muenter and V. W. Laurie, J. Am. Chem. Soc., 86, 3901 (1964). J. S. McKnight and W. Gordy, Bull. Am. Phys. Soc., 14, 621 (1969). E. Hirota and C. Matsumura, J. Chem. Phys., 55, 981 (1971). E. Hirota and C. Matsumura, J . Chem. Phys., 59, 3038 (1973). E. Hirota and M. Imachi, Can. J . Phys., 53, 2023 (1975). E. Hirota, K. Matsumura, M. Imachi, M. FuJIo, Y. Tsuno, and C. Matsumura, J . Chem. Phys., 66, 2660 (1977). S. C. Wofsy, J. S. Muenter, and W. Klemperer, J. Chem. Phys., 53, 4005 (1970); I. Ozier, W. Ho, and G. Birnbaum, J . Chem. Phys., 51, 4872 (1969). T. Tanaka, C. Yamada, and E. Hirota, J. Mol. Spectrosc., 63, 142 (1976). K. Tanaka and T. Tanaka, J . Mol. Spectrosc., 69, 335 (1978). K. Matsumura, K. Tanaka, C. Yamada, and T. Tanaka, J . Mol. Spectrosc., 80, 209 (1980). A. Baldacci, S. Ghersetti, S. C. Hurlock, and K. N. Rao, J. Mol. Spectrosc., 59, 116 (1976). R. Anttila, J. Hietanen, and J. Kaupplnen, Mol. Phys., 37, 925 (1979). Y. Endo, S. Saito, E. Hirota, and T. Chikaraishi, J . Mol. Spectrosc., 77, 222 (1979). A. G. Maki, J . Phys. Chem. Ref. Data, 3, 211 (1974). D. F. Eggers, Jr., I. C. Hisatsune, and L. Van Alten, J. Phys. Chem., 59, 1124 (1955). W. M. A. Smit, A. J. Van Straten, and T. Visser, J . Mol. Struct., 48, 177 (1978). G. A. Segal and M. L. Klein, J . Chem. Phys., 47, 4236 (1967). G. Strev and I. M. Miiis. J . Mol. Soectrosc., 59, 103 11976). A. R. Hby, I. M. Mills, and G. Strey, Mol. Phys., 24, 1265 (1972). T. Nakagawaand Y. Morino, Bull. Chem. SOC.Jpn., 42, 2212 (1969). W. J. Lafferty, R. D. Suenram, and D. R. Johnson, J. Mol. Spectrosc., 64, 147 (1977). Ya is a transliterationfrom the Cyrillic alphabet of a character which is not available.
Single-Pulse CO, Laser-Induced Oxidation of Ammonia Phacrdon Avouris IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598 (Received October IS, 1979) Publication costs assisted by IBM
The single-pulse C 0 2 laser-induced oxidation of NH3by 02,N20,and NO is reported. Time and spatially resolved emission spectroscopy is used to study the concurrently emitted luminescence. The effect of the laser is in this way traced to the production and radiative heating of a plasma. The system NH3-N20 is studied in detail. The nature and time dependence of the concentration of the electronically excited radicals are investigated. Evidence is presented for the chemical excitation of the OH radical. The chemical mechanism of the explosive oxidation is discussed. Introduction In the past few years we have witnessed a great deal of activity in the area of multiphoton infrared laser &emistry.1 The early realization of isotopic selectivity has created hope for isot;opeseparation on an industrial scale. However, isotope separation is not the only advantage of inducing chemistry by lasers, The multiphoton infrared
chemistry itself is plagued by low conversion since chemistry usually takes place only in the focal volume of the beam. If, however, one is not interested in isotopic selectivity, significant chemical conversions can be initiated by the high density of free radicals produced at the focal volume. This can be accomplished either through radical chains or by the radicals acting as catalysts for other types
0022-3654/80/2084-1797$01.00/00 1980 American Chemical Society
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of Physical Chemistry, Vol. 84, No. 14, 1980
of reactiom2 An analogous situation was realized recently3 in the C02laser-initiated thermal isomerization of CH3NC. In this case the heat evolved by the laser-converted molecules initiates a thermal explosion. The COz laser-induced chemistry of NH3 has been the subject of several ~ t u d i e s . ~The - ~ conversion is_ very low and the products of the dissociation $re NH2(X,2B1),H(1%)and, to a very small extent, NH2(A1,2Al).5~6 Recently, Lin and Bertran7 reported the quantitative reaction of a mixture of 50 torr of NH3 and 50 torr of O2 after being subjected to a single CO, laser infrared pulse. The reaction was accompanied by the emission of a strong yellowish luminescence. However, no information was provided concerning the nature of the laser action, the mechanism of the reaction, or the origin of the luminescence. In this paper we attempt to answer the above questions through temporally and spatially resolved spectroscopic studies. Three different oxidizers, 02,N20, and NO, have been utilized with similar results. However, most of the presented results are from the NH,-N20 system. The advantages of pulsed laser initiation and time-resolved monitoring of the reaction are demonstrated.
Experimental Section All the gases used were Matheson research grade products. The reaction cell was an aluminum cylinder, 15 cm long and 3 cm in diameter, equipped with NaCl entrance and exit windows and a Suprasil side window for the viewing of the luminescence. The cell was connected to a vacuum system, and the pressure of the reaction gases was measured by a Baratron capacitance manometer. The C 0 2 laser was a Tachisto TEA laser tuned to the 10.72-pm P(32) line. The infrared pulses were focused into the reaction cell by a 10-cm focal length BaF, lens. The luminescence was spectrally and temporally resolved by the combination of a 0.3-m Ebert monochromator and a gated optical multichannel analyzer (OMA-2 Princeton Applied Research). Results and Discussion Single COz laser pulse, explosive oxidation of NH3 was observed in 1:l mixtures of NH, with 02,NzO,or NO when the total pressure was about 100 torr or higher. Infrared spectra of the product mixture showed a total consumption of NH,. The main infrared active product in all mixtures is H20. In the case of the NH3-02 mixture, some NzO is found as a final product. This is in agreement with the findings of Lin and Bertran.7 The oxidation of NH, by all three oxidants is accompanied by a strong luminescence. Visually, this luminescence appears as a strong, uniform yellow glow encompassing the whole volume of the cell. However, detailed spectral studies show it to be spatially and temporally dependent. ( a ) The Mechanism of the Laser Initiation of Oxidation. An insight into the way in which the laser initiates the oxidation of NH3 is provided by the study of the light emission from the focal volume of the COz laser beam. In the following, we present results obtained on the NH,-N,O system. Time-integrated spectra show very strong H-atom Balmer lines (Ha, H,, H,) along with weaker lines from N+ ions. The emission spectra have a very informative time dependence. At small delays after the C02laser pulse the lines are very broad, becoming progressively narrower at longer delays. In Figure 1,we display such a time-resolved spectrum. A t early times, a broad line centered a t about 658 nm (H,) is seen overlapped by a shorter wavelength continuum. As the delay increases, the H, line narrows, and the continuum intensity decreases. After blanking out
Avouris
500
550
600
650
700
WAVELENGTH lnm)
Flgure 1. Luminescence emitted from the focal region of the laser beam in a mixture of 80 torr of NH, and 120 torr of N20: top, the emision spectrum obtained with a delay of 500 ns after the COP laser pulse, gate width 40 ns; middle, the spectrum after 4 ps, gate width 40 ns; bottom, the time-integrated spectrum showing various transitions of N'. The H lines have been blanked out.
the strong H, and H, emissions, the time-integrated spectra show the presence of a number of N+ ion emission lines in the same spectral range as the continuum. The above observations cannot be accounted for by the usual mechanisms of line broadening, specifically Doppler, collisional, and power broadening. The sum of the contributions of all these effecta to the line width is calculated to be negligible (- 1A). However, immediately after the COz laser pulse, the observed Balmer (Hp) line widths (fwhm) are -100 A. This extreme broadening can only be a result of strong internal Stark fields.8 These internal electric fields imply the formation of a laser-induced plasma at the focal region of the laser beam. The production of a plasma is also necessary in order to explain the presence of high-energy species, such as excited H and N+ species. Note again that the low-pressure infrared multiphoton dissociation of NH, gives ground;state NH2 and H and, to a very small extent, excited NHz(X2A1) radical^.^^^ The conclusion that the reaction is not photochemical, as claimed by Lin and Bertran,' is also supported by the fact that the laser can induce the reaction at frequencies that are not resonantly absorbed by NH3. Lin and Bertran7 observed that the reaction could be induced either by the 10.719-pmP(32) and 10.319-pmR(10) lines, which are absorbed by NH,, or by the 10.551-pm R(16) line, which is not absorbed. Unlike photochemistry, plasma formation does not require the absorption of the light by the molecule^.^-^^ Given the production of the laser-induced plasma, the time dependence of the spectra can be explained by the progressive dissipation of the plasma in time, and of the concurrent reduction of the Stark fields. The H, line is particularly sensitive to Stark fields and also far less sensitive to radiative transfer effects than Haas The H line width has, therefore, been used to obtain the laser-incfuced plasma density. The electron density ne is related to the full Stark width A& by ne = c(ne,T)Ah,3/2,where the coefficient c(ne,T)is only weakly dependent on electron density. After correcting for instrumental broadening using the lines of a low-pressure Hg discharge, analysis of the line widths according to Wiese et a1.I2 gives the required ne. Thus, in a mixture of 100 torr of NH3 and 100 ~. torr of N20, the initial ne is found to be -lo1' ~ m - From the time dependence of the line width we find that the plasma dissipates in -15 ps. It should be stressed that in our experiments the laser peak power was kept lower than the peak power (1 GW/cm2) utilized by Lin and Bertram7 Under these conditions, plasma formation was detected in all mixtures containing more than -30 torr of NH3, irrespective of the total mixture pressure and the
COP Laser-Induced Oxidation of NH,
The Journal of Physical Chemistry, Vo/. 84, No. 14, 1980
1799
II
500
550
600
650
700
WAVELENGTH inm)
Flgure 2. Visible luminescence observed at -2.5 cm from the focal volume in the direction of the beam propagation: mixture composition, 80 torr of NH:, plus 120 torr of N20; top, spectrum obtained after a delay of 1 ms, gate width 1 ms; bottom, spectrum obtained after a delay of 3 ms, gate width 1 ms.
type of the oxidant, 02,NzO, or NO. However, chemical explosion is observed only when the total pressure exceeds -100 torr, In the e.rrplosive mixtures the bluish plasma emission cannot be seen by the naked eye as it has been masked by the strong yellowish luminescence. The origin of the plasma can be traced to acceleration of a few free electrons in the sample by the laser through the inverseBremsstrahlung effect,9'11s12Le., through laser-induced free free transitions of electrons in the field of neutrals and ions. (Intrinsic ionizations, as a result of multiple-photon infrared absorption, analogous to the one recently reported,13 does not occur in The accelerated electrons can induce secondary electron-impact ionization and the cycle can be repeated. The rate of energy absorption by the free electron is given by deldt = (e2E2/mw2)v,ff,4-11 where E is the electric field of the light, w is its angular frequency, and veff is the effective collision frequency. It is thus seen that the effect is pronounced at higher pressures and at infrared frequencies. The laser-induced plasma is not strictly localized in the focal volume of the laser. It is formed as an elongated plasma along the direction of the laser beam. It extends 1.5 cm from the focal point in the direction opposite to the propagation of the beam and -0.5 cm in the other direction. This shaple of the laser-induced plasma can be understood in terms of the current hydrodynamic theories of radiative heating of plasmas and of plasma expansi0n.l' The radiative heating of the initially produced plasma results in a shock wave propagating opposite to the laser beam. The propagation velocity D is given approximatelyll where So is the peak power and p is the by D = (S,,/P)'/~, density. For a mixture of 100 torr of NH, and 100 torr of lo6 cm/s. N20, the shock wave is supersonic with D The temperatures produced by the shock wave are very high, as is evident by the extensive ionization produced. The high temperatures and large concentrations of free radicals and ions produced by the laser-induced shock wave initiate the explosion that leads to the quantitative oxidation of NH,. ( b ) The Free-Radical Luminescence. Outside the plasma region the emission has a completely different spectral and temporal distribution. A luminous wave is initiated near the folcal volume, and our studies show it to propagate outward with a velocity of ?lo3 cm/s. In the near-UV the most promjnent bands of the luminous wave are the OH* A2Z+ -* XzII and NH* A311 X3Z emiss i o n ~ In . ~the ~ visible, the strong ammonia a! bands listed by Fowle: and Badanii,16and now identified with the NH2* AzA1 X2B1transition,15are found on top of a continuum emission. From its spectral distribution, short wavelength spectral cutoff of -4000 A, and its analogy to the emission observed in the reaction of NH3 with atomic ~xygen,~' the continuum is assigned to the inverse predissociation NO
100
-
I
'
,
.
*
'
,
0
4)
-
.
0
t z 0
m
4
>
5
,
'
0
OH
(6'Z'-?
A
NH
(x371
71
-? 'X*)
IO-
1
-
z
H5
Ii
*
A A
A 'I
i
i
i
S
i
i
i
s
-
-
-
-
-
+ 0 NOz -thv. We have observed the same emissions in the NH3-Oz system. Time-resolved spectra, obtained at -2.5 cm from the focal point in the direction of the beam propagation, are shown in Figures 2 and 3. In Figure 2,the NH2* bands and the NO + 0 continuum are shown. Within our time resolution (1ms), determined by signal-to-noise considerations, both emissions appear simultaneously. However, the NH2 emission is prominent at short delays while the continuum dominates at longer delays. The emission appears almost featureless after about 5 ms. However, no NO or NO2 could be detected in the final products. This is in agreement with the mass spectral analysis of the products of the NH3-02 reaction by Lin and Bertran.' The time-resolved emission spectra can be used to follow the time dependence of the OH* and NH* concentrations. Typical spectra, obtained about 2.5 cm from the focal point in the direction of beam propagation, are shown in Figure 3. In Figure 4 we show the variation of the peak intensity of OH* measured on the 0-0 band at about 3090 A (head of the Qz and other overlapping lines, particularly from the Q1branch) and of NH* peak intensity at 3360 A (Q branch of 0-0). As can be seen from Figure 4, the two time dependences are completely different. In a stoichiometric mixture, the OH* attains a maximum at -6 ms, while the NH* decreased monotonically. The si-
1800
The Journal of Physical Chemistry, Vol. 84, No. 14, 1980
Avouris
multaneous appearance of the two radicals and their different lifetimes occurs as a result of the various equilibria established after the explosion (see subsequent discussion). (c) Thermal us. Chemical Excitation. By comparing the I emission intensity from the 0-0 and the hot bands of OH* as a function of time, and provided that the molecular excitation is thermal, a measure of the time variation of the temperature of the system is obtained. Under this assumption, at -2.5 cm from the focal volume in the direction of the beam propagation, the temperature increases and attains a maximum at -6 ms after the laser pulse. However, although the observed excitations are certainly 260 300 320 340 to some degree thermal, it is also possible that chemical WAVELENGTH (nmj excitation contributes to the production of excited states. Most chemi-excitation mechanisms produce excited molFigure 5. The effect of mixture composition on the near-UV emission; ecules in specific vibronic levels. Thus, in a case of mixed time-integrated spectra obtained at -2.5 cm from the focal volume: top, 110 torr of NH3 plus 90 torr of N,O; bottom, 50 torr of NH3 plus thermal and chemical excitation, one does not expect that 150 torr of N,O. a common temperature can account for the populations in all vibronic levels. This fact can be used as a test for chemi-excitation.ls The OH excitation appears best suited for such investigation, since several vibronic bands can be seen in emission. Under the explosion conditions, the electronic quenching is very strong and therefore minimal -9 vibrational relaxation takes place. The ratio then of the > population (N) of a level with u’ = n to the population of the level u’ = 0 is given by r z N,/No = ( ~ n ~ - ~ ~ ~ / ~ o ~ ~ ~ ~ ) ((i&~~~/Fnf.+,,p) Ao/-of~/A,~-~,~) m (1) where I is the emission intensity, A is the Einstein coefficient, and 5 is the transition frequency. The superscripts 500 550 600 650 700 ’ and ” refer to the excited and ground state, respectively. WAVELENGTH Inml In the case of thermal equilibrium the population ratio is Flgure 6. The effect of mixture composition on the visible emission; related t o the temperature by time-integrated spectra obtained at -2.5 cm from the focal volume b-
-
N,/No
exp[-(E, - Eo)/kTI
-
(2)
where E,, and Eoare the excitation energies of the transitions n’ 0” and 0’ O”, respectively. Applications of eq 1 and 2 to the 0’-0”, 1’-0’’, 2’-1” and 3’-2” bands of OH (2Z+-211) as described by Kaskanls gives the following vibronic temperatures: T -1800 K(u’ = l), T -3200 K(u’ = 2 ) , and T -4000 K(u’= 3). These results are very similar to the results of Kaskan on the H2/02/N2 flame.18 They indicate that chemi-excitation does participate in the production of OH %+. There are several chemi-excitation mechanisms that could be involved in the explosion. Among the strong candidates is the well-studied direct bimolecular association of H(12S)and O(,P) atoms19>20
-
-
O(,P) + H(%) OH(‘%) OH(2X+)u’= 2 and 3 (3) Strongly exothermic trimolecular recombinations such as OH + OH + H OH(’X+)u’ > 0 + HzO (4)
-
+
H
+ H + OH
OH(’2’)d > 0
+ H2
(5)
0 + 0 + OH OH(2X+)~’ > 0 + 02 (6) may also contribute to chemi-excitation.1s~21~2z The presence of free 0 atoms in our system is indicated by the observation of the NO + 0 emission continuum. Free H atoms are also produced, mainly by the thermal dissociation of the various NH, species. ( d ) The Chemical Mechanism of the Explosion. Through plasma formation at the focal volume, radiative heating of this plasma, and formation of a shock wave, the infrared laser produces high temperatures and high concentrations of free radicals and charged species. These conditions initiate the explosion. +
in the dlrection of beam propagation: top, 110 torr of NH3 plus 90 torr of N,O; middle, 80 torr of NH, plus 120 torr of N20; bottom, 50 torr of NH, plus 150 torr of N,O. The peak at 589 nm Is due to Na from the NaCl windows.
The explosion is of both thermal and free-radical chain nature. The fact that the thermal dissociation of NH3 and NzO is extensive can be demonstrated in experiments with nonstoichiometric mixtures. The infrared spectra show no significant amounts of NH, or N 2 0 remaining after nonstoichiometric mixtures have been exploded by a C02 laser pulse. Evidence of the thermal dissociation is also seen in the emission spectra. Figure 5 shows the timeintegrated emission in the UV from two nonstoichiometric NH3-N20 mixtures. Compared to a stoichiometric mixture, the NH3-rich mixture is characterized by a low temperature and a low OH*/”* ratio. The low OH*/”* ratio can be explained by the thermal decomposition of the excess NH3 to NH2,which is further degraded to NH thermally or through H-abstraction reactions with H and NH2. The opposite behavior is seen in the “,-poor mixture. An analogous picture is seen in the visible (Figure 6). “,-rich mixtures show strong NH2* emission, while “,-poor mixtures show essentially only the NO + 0 continuum. The free-radical reactions involve monoradicds (€3, OH, NH2) and biradicals (0,NH). The atomic oxygen resulting from the dissociation of N 2 0 probably does not play a significant role in the degradation of NH,. This is suggested by early studies of the interaction of NH, with 0 at room temperature.17 Oxygen atoms, however, react with NH, and NH, + 0 NH + 0
+
+
OH NO + H
(7) (8)
J. Phys. Chem. 1980, 8 4 , 1801-1805
The NO reacts with NH2 and NH and becomes consumed as follow^^^-^^
+ N O + N z + OH + H NH 1- NO 2" + OH
NH2
(9)
(10)
Reaction 10 is very exothermic (96 kcal/mol) and can produce excited OH("P). This reaction should contribute to the observed behavior seen in Figure 4.
Conclusions We have shown that the mechanism by which the C02 laser induces the single-pulse oxidation of NH3 involves the production and radiative heating of a plasma. Time and spatially resolved emission spectroscopy was used to characterize the nature of the emitting radicals, their time dependence, and the nature of the excitation mechanism. Chemi-excitation was5 shown to be an important electronic excitation mechanism for the OH radical. The initiation of a free-radical or thermal chain reaction by a laser through a laser-induced plasma may be quite generally applicable. The fast initiation by the short-duration laser pulse makes the chemistry more amenable to time-resolved mechanistic studies. Another advantage refers to the spatial properties of the laser initiation which can be utilized to avoid heterogeneous chemistry on the wall surfaces and surface quenching. Acknowledgment. I thank Mr. Y. Thefaine for his expert technical assistance.
References and Naites (1) P. A. Schultz, Aa. S. Sudbo, D. J. Kralonovich, H. S. Kwok, Y. R. Shen, and Y. T. Lee, Ann. Rev. Phys. Chem. (1979);R. V. Ambartzumian and V. S. Letokhov in "Chemical and Biochemical Applications of Lasers", Vol. 111, C. B. Moore, Ed., Academic Press,
1801
New York, 1977;N. Bloembergen and E. Yablonovkch, fhys. TCday (May 1978). (2)J. H. Clark, K. M. Leary, T. R. Loree, and L. B. Harding, Sprhger Ser. Chem. Phys., 4, (1978). (3) D. S.Bethune, J. R. Lankard, M. M. T. Loy, J. Ors, and P. P. Sorokin, Chem. Phys. Lett, 57,479 (1978). (4) V. S.Letokhov, E. A. Ryabov, and 0. A. Tumanov, JETP, 36, 1069
(1973). (5) J. D. Campbell, G. Hancock, J. B. Halpern, and K. H. Welge, Opt. Common., 17,38 (1976);Chem. Phys. Lett. 44, 404 (1976). (6)P. Avouris, M. M. T. Loy, and I. Y. Chan, Chem. Phys. Lett., 63,
624 (1979). (7) C. T. Lin and C. A. Bertran, J . Phys. Chem., 82, 2299 (1978). (8) H. R. Giem, "Spectral Line Broadening by Plasmas", Academic Press, New York, 1974. (9)C. DeMichellis, IEEE J. Quant. Nectron., QE-5, 188 (1969). (IO) C. G. Morgan, Sci. Prog. (Oxford), 65, 31 (1978). (11) Yu. P. Raker, "Laser-Induced Discharge Phenomena", Consultant Bureau, New York, 1977. (12) W. L. Wlese, D. E. Kelleher, and D. R. Paquette, Phys. Rev. A , 6, 1132 (1972). (131 . . P. Avouris. I. Y. Chan, and M. M. T. LOY,J . Chem. Phys., 70,5315 (1979). (14) P. Avouris, 1. Y. Chan, and M. M. T. Loy, J. Chem. Phys., 72,3522 (1980). (15) R. W. B. Pearse and A. G. Gaydon, "The Identification of Molecular Spectra", Chapman and Hall, London, 1976. (16)A. Fowler and J. S. Badami, Proc. R. SOC.London, Ser. A , 133, 325 (1931). (17)G. E. Moore, K. E. Shuler, S. Silverman, and R. Herman, J. Phys. Chem., 60,813 (1956). (18) W. E. Kaskan, J . Chem. Phys., 31, 944 (1959). (19) S.Ticktin, G. Spindler, and H. I. Schiff, Discuss. Faraday Soc., 44, 218 (1967). (20) M. Charton and A. G. Gaydon, Proc. R. SOC.London, Ser. A , 245, 84 (1958). (21)C. Bernand and P. J. Van Tiggelen, Deuxi6me Symposium Europgen sur la Combustion. The Combustion Instltute. OrlQans. 1975. (22)M. G. Davis, W. K.'McGregor, and A. A. Mason, J. Chem. Phys., 61, 1352 (1974). (23) M. P. Nadler, V. K. Wang, and W. E. Kaskan, J. Phys. Chem., 74, 917 (1970). (24) J. N.'Mulvlhill and L. F. Phillips, Chem. Phys. Lett., 35, 327 (1975). (25) S.Gordon, W. Mulac, and P. Nangia, J. phys. Chem., 75,2087(1971). (26) G. Hancock, W. Lange, M. Lenzi, and K. H. Welge, Chem. Phys. Lett., 33, 168 (1975).
Radlation-Induced Reactions of Antimony and Tellurium Compounds in Sulfuric Acid Solutions Hlrotake Morlyama,"' Ichiro Fujlwara, and Tomota Nishi Institute of Atomic Energy, Kyoto Un/versity, Uji, Kyoto 6 11, Japan (Received August 20, 1979) Publication costs assisted by Kyoto University
-
In deaerated 0.4 M HzS04solutions containing both Sb(II1)and Sb(V),Sb(II1)was oxidized to Sb(V)and Sb(V) was reduced to Sb(II1) by y rays. The initial yield of reduction Gi(Sb(V) Sb(II1)) increased linearly with the ratio [Sb(V)lO/[Sb(III)],,, that of oxidation Gi(Sb(III) Sb(V))increased with increasing Gi(Sb(V) Sb(III)), and the overall yield of oxidation Gi(Sb(V))= Gi(Sb(III) Sb(V))- Gi(Sb(V) Sb(II1)) was constant and equivalent to the primary yield of hydrogen g H , = l/Z(goH - g H ) + gHzOz. A possible mechanism of y-ray-induced reactions in deaerated solutions was proposed in which Sb(II1) was reduced by H and oxidized by OH, Sb(I1) was oridized by HzOz,and Sb(IV), and the disproportionation of Sb(1V) to Sb(II1) and Sb(V) followed. In the presence of Sb(V),reduction of Sb(V)by H gives the same stoichiometry. The results on Te(1V) and Te(V1) in 0.012 M HzSO4 solutions support a similar sequence to that of the antimony system, in which the unstable valence states Te(II1) avd Te(V) play an important part.
--
Introduction The yields of radiolysis of several redox systems including Sb(III)-Sb(V)2-4and Te(IV)-Te(VI)5 have been investigated by the use of y rays from a COCO source. Matsuura et a1.2have reported that Sb(II1) in aerated 0.4 M HzS04and 0.8 M HC1 solutions is oxidized to Sb(V) by OH and HOz radicals with G(Sb(V)) of -3. They have 0022-3654/80/2084-1801$01 .OO/O
-
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also found that the yield of oxidation in deaerated solutions is quite lower than that in aerated solutions. The latter fact suggests that reduction by H atoms takes place in deaerated solutions and competes with oxidation by OH radicals. A similar finding on the tellurium system was reported by Haissinsky et al.5 They attributed the decrease of the yield of oxidation to the occurrence of re-
0 1980 American Chemical Society
