11. W. MATTHEWY, H. A. MAHLMAN, AND T. J. SWORSKI
2680
Elementary Processes in the Radiolysis of Aqueous Nitric Acid Solutions: Determination of Both GO, and
GNOalv2
by R. W. matt hew^,^ H. A. Mahlman, and T. J. Sworski* Chemastry Division, Oak Ridge Aiatwnal Laboratory, Oak Kidve, Tennessee
37830 (Receiaed Marcli 27. 1972)
Publication costs waisted b y the U . S. A t o m i c E n e r y y C o m m i x s w n
Kinetic evidence is presented for concurrent prodrictiori of two oxidizing radicals in the radiolysis of aqueous 4.0 11%nitric acid solutions: 01-1arid NO, radicals tliat are presumed to result from the direct interaction of iotiiziiig radiation with water and nitric acid species (NO,.- and HXO,), respectively. The eviderire was obtaiiied from the dependence of C(Ce”1) on cerium(I1J) and formic acid conccntrat,ions i r i the radiolysis of cc:riurn(lV)-cerium(II1)-formic acid mixtures in air-saturated 4.0 M nitric acid solutions with W o y radiwt,ion. Goa = 2.04 f 0.09 arid G N O=~ 1.56 0.12 were determined with the use of ti computer to fit espeririieiit:~l (lata by the method of least squares to a kinetic equation cotitaitiiiig 13 dependent variables. We assume that energy is partitioned between water arid nitric acid species in proportion to their electron fraction. I f t h i s be true, then there is 110 evidence for oxidation of iiitric acid species by precursors of OH radical such as H 2 0 + sirice C ~ O Hwas found to be proportioiial t o electron fraction water.
*
Introduction Thc import;zncv of the S O &radicsl as an intermediate i n thc rudiolj sis of : ~ q u c ~ nitric ~ s acid solutions has b w n t hr subjwt or num(’rout, invvstigations. Four dtffcrthnt procc~ssc’shavv bwn proposed for thv produrtioii of SOi r:dic:il. rcactioii of OH radic’al ith nitratt. ion in nitric acid solutions;* direct interaction uf ionizing radiatiori Lsith nitratc ion,5 rcaction of NO2 w i t t i 0 atom:b : ~ n d rcaction of riitr:ito ion with HsO + .* ?’ho proposal that OH radic;tl is a prcicursor of SO, radicd in rritric. iicui solutions has bwn subst a n t i a t d by pulsc radiolysis tcvhniqucs.” Thc cffcc.ts of pH on S O , radical pi‘otluction indicLatc that thc ratch of rwciion of O H r3dic:tl \ b i t t i nitrat(. ion is w r y small, if I t occurs :it ail, and that SO, radical ari rcac~tionof OII r:idicz;il u it h undissociated nitric. acid. Thcw dfccts 01 ptf tiitvc btwi contirmcd by flash photolysis tc~rhnlc~ucs ‘‘I Tht. proposal that S O , radival is produced by intcAraction of iorlizing radiation rcith riitratc, ion has bccn wbsf ttntiatcd by pdlsc radiolysis techniques. l 1 Tho dcpcmirnc~~ of KO,% rdicaal pic.lds on dosc itrid scavcmgcr cmwmtratioriS hou cw’r, r i as intc.rprctcd as c1vidcnc.c that SO,rdic.al IS tiot cmtircbly producd by & t i clrrncwtary prowss scch als ionization. It n rn suggested t h:xt disiociativc$ iorrizl-ltion yicxlds NO?, 0, and P- in :i “c.:igy.” SO, r:idic~il produvtion u a s assutwd to oc.(>uiby r(wstioii 01 KO21~1th0 atom in ciithcr the c q y , thv spur, o r t1iv hull\ oi’ t h c iolution. Thc wtdciicc for dissociativc~ ionixu,t i o n 1 5 qu~stionablt~ siticc. the w n vliisiotis froin sravc~rigc’rrtudic’s w r c ~vonflicting: (1ssc.ntiaily noiw of 11-tcl 0 :Itoms (=xsap(’from thv spur for hut ut Imst half of thr 0 atoms c~scapc ifom thc spur foi piilw r : i d i o l y ~ s . ~
‘
The proposal that KO3 radic.;il is producwl by r ( w tion of nitratr ion with H 2 0 f has bwri rclfutcd by pulsc radiolysis tcchniques, at I w b t for rrt~utralsolutions.”,” Thc NOj radival yiclld 111 wutral wlutions u as fouiid to bt. 2% lincw function of thc c~ic~rgy absorbod by iiitratc. ion uith no (witribtition from crwrgj- absorbed by w t w . In avid solutions, iiowwu, t h(. SO, radical yiclld i w s found t o incrc;Ls(’ noiilincurly n ith iricrtlasc in nitrat(> ion concentration and a p p r a r d to be rcaching a limit.6 This dcpc.ndrncr oi SOI radical yield on nitratc. ion wiicmtration in : ~ c . i d mlutioiis has bcvn t o rcaction of nitratv ion with Hi()+, an c~xamplrof h o l ~trapping by anions that M as portulatrd in :L modcl for thci radiolysis o1 \v:itt.r b:~scd on primordial, isolated singic HrO+ -P - p a i ~ This p q w r roports thc rwults from ;L 1;inctir nn:alysis of t h(>depcmkncc. of G(Cc”’) on mice acid cwnct.ntrations in thc radio (3
(1) Itesesrdi sponsored by the U. S. Atomic Energy Commission under contract with Union Carbide Cork). (2) This paper w:is presented in part at the X S I I International Congress of Pure and Applied Chemistry, Sydney, Australin, August 20-27, 1969. (3) Guest Scientist from the Australisu Atolriic l h e r g y ( h i m i u s i o n , Research Establishnient, Lucm Heights, N e w South W;tles. (4) I T . ‘ h u b e and W.C . Briiy, -1.Amcw. C h ~ n r Soc., . 62, 3357 (1940). (5) 3. Bedriar and 8 . Lukac, Coll~ct.Czech. (?hem,. Commz~n.,29, 341 (1964). (6) M . I>ariicls, .I. Phys. Chem., 73, 3710 (19(i9). (7) M . l):tiiiels arid E. E. Wig#, ibid., 73, 3703 (1969). (8) J. Bednar, Collect. Czech. Chem. Cornmiin., 27, 2204 (1962). (9) I?, K. Brosskieuicz, Int. J . A p p l . IZadiat. Isotop., 18, 25 (1967). (10) I,, Dogliotti arid 15. Hsyon, J . I ’ h ~ / s(‘hrm., . 71, 380‘2 (1967). (11) bl. I);iniels, ibid., 70, 3022 (1966). (12) T. Suw:ri ;tiid W. €I. IIamill, J . (,’hem. f’hps., 52, 3443 (1970). (13) W. 11. Ha~nill,J . I’hyY. C’hern., 73, 1341 (1969).
eeriuni(IIlj-formic, :wid mixtures in air-suturatc.d 4.0 LW nitric :wid solutions v, ith Wo y radiation. As rrpxtcd ~onirnunication,~~ evidmcc is prc111'1 cwt production of tx o oxidizing r:dwals that prcsumrd to he OH arid NOa Our r1~sti1ib cwniirni thc pruporai* that] OH rstdical rcwts 111 nitric. :wid soint lone; to produw t,hv KOa radical. They rr.fut t' t h r a strgfysticm" that nitrate ion reacts with €I,O 1 111 acidic solution,. sinw (;,)I3 is proportional to cl1cc.tron fract ion w n i c ~ u
Experimental Section Nnt/.r i d s . dT Ihdcrick Smith Chcmical Co. cerous nitratv hydratpd and Baker Analyzed ceric ammonium nitrutr formi(*acid, and nitric wid wcrc used without furtlicr purifi~atiori. All solutions were prepared with w t c r from s 13anis;md still that was further purificti ivr distillations from an acid dichromat(. solution, from :in sl kaline permanganate solution, and 5 finally from :til all-silica system into silica storage ves0.001 0.0 1 0 .' ) 9.0 scls All solu Iions wprc :~llourd to stand overnight [HCOOH], M b(.for(.bciog it.r:Ldi:Lt c ~ t 1-1 7 udicttio,,,. Pjoiui ions in 2-ern vylindrical absorpFigure 1. Ilependence of G(Ce"') on [Cei"] and ~ l - I C O O ~in I] the radiolysis of ceri~~m(IV)-ceriurn(II) -formic acid mixtures tion rclls v,cr(i irnidiatcd in @ C osourccs of the Crhormin air-sat,urated 4.0 M n h i c acid solulioiis with COCO y ~ ~ r:ttcs in solution w r c 1 ( ~ ~ - 1 ~ o ( ~ h it~l n( a~ dg~1~1!.Ilose radiation: initial [Ce"'] = 0, 5.0 x io-" M; 0 , 1.0 x dt+mniricd 11 i t h tlic, ferrous sulfato dosimctcr using M ; 1-1, 2.0 x tO-$ M ; V, 5 . 0 x 10-$ M ; I-, 1.0 x 10-2 M ; C(Fv7*') = 1 ,5.t;16 and L: molar extinction rocflicicnt M ; A, 4.0 x 10-8 M ; 0 ,.i.O X 1 0 - 2 M . X, 2.0 X of 2210 for iron(111) :it 303 rim and 25" in 0.4 AB sulCurves are theoretical and represent letast8-sqriaresfit of the data to eq I. furic acid solut~ons* 7 The rnrrgy absorbed in 4.0 ild nitric' :wid ~po!utioiib rniativr to thc ferrous sulfate dosimc t w ~ + s msumcd s t o be i n the ratio of c h k x i denchanges in crrium(1V) c.onc~cntration n.cw approxisitiw. mately :I linear function of dosc, c w q t for thc boiiiAnahyses. i h n g r s in cerium(1V) concentration tioris with Ihe lo^ (1st ccriuin(lI1) c,oncc.ntrations of R 11h incwasc in :\bsorbcd dosc wcr(' detrrmincd spw1.0 X lo-? and ~ncrt~mcnt s. Thc irradiation ~ ~ ~ (Pyrocell 11s reduction d(wwiscti only slightly with incrcmcl in tiosc, Manulttcturinq (h) had S18-260 silica a indows that t h r initial vi~liicsfor G'(C(J1') w r c rst iinstcd from plots did not hecmnc colorrd enough during irradiation to of t hr (8ti:~ngcsi n ccriurn(IV) conwntmf ion for P : L C ~ i n i c d ' c w nit 11 tlic analyses. A molar c.xtinc.tion codow increment :a5 a funcbtion of daw. c.fhcicnt f o t w i i u n ~ ( ~ l 'in ) 4.0 M nitric8 acid solutions of 3670 at 345 nirr \I :IS drtcrminrd rclativc to jX30 at Discussion 320 iiin In 0 4 , I f sulfuric acid solutions.1fi T h r dfrct of formic acid on thr ratiioivsis of aqueous inorganic solutions has bccri well c\stablishcd T h o OH radical, which can oxidizcb both ironfll)Ix and cvr i ~ r n ( 1 1 1 )ions, ~ ~ roacts with formic. acid to yirld thc COOH (or HCOO) radicd,20 u hich w n rcductb both (14) It. W. Xstthews, H.A. Mahlrnitn, mid 1'. J. Sworuki, J . P A g s . ChPrn., 74, 3x35 (1970). (15) J. A. Ghorinley sild ( z . .J. Hoch:tn:tdel, &I;. S c i . ~ 7 ~ s t r r r m22, ..
473 (1951). (16)
(:. 5 . Hochatiadel and J . A. Ghonnlcy, J . ( ' h e m . I'hys., 21, 880
( 1 9.53).
(17) 'r. .J. Sworski, Radiat. Res.. 4, 483 (1956). (18) 1". f1:tber and .J. Wciss, .Vaturwis.sen,scchn/ten,20, 948 (1932). (19) ,J. Wciss and 1). Porret, Nnt7~7.e(Londo/i). 139, 1019 (1937). ( 2 0 ) 11. T:iuJN?.J . Am,er. ('hrm,. Soc., 63, 2453 [1941).
R. W. MATTHEWS, H. A. MAHLMAN, AND T. J. SWORSKI
2682 iron(III)21 and c c r i ~ m ( I V ions. ) ~ ~ ~In ~ ~sulfuric acid solutions, the OH radical also reacts with sulfuric acid ,~ can either oxanions to yield the $301-r a d i ~ a lwhich idize cwium(II1) ionz4 or react with formic acid t o yield the COOH (or HCOO) radical.26 The dependence of G(CcIrlj on ccrium(II1) and formic acid concentrations in the radiolysis of cerium(1V)-cerium(II1)formic acid mixtures in 4.0 M sulfuric acid solutions yielded kinetic evidence for concurrcnt production of OH and Sod- radicals in the radiolysis of aqueous sulfuric acid solutions.26 Determinations of Both GOH and G N O ~ .T o explain the dependrntc of G(CeIT') on cerium(II1) and formic acid concrntrations in the radiolysis of cerium(1V)ccrium(III)-formic wid mixtures in 4.0 M nitric acid solutioas, 1% e have considered the following reactions of O H and KC; radicais.
-+
+
OIi -C H + KO3H20 NO3 01%1-CelI1 --e+OHCeIV
+ SO8 + Ce"1 +NOa- + Ce'V OH + HCOOH +H,O + COOH KO3 + HCOOH + Hf + COOH COOH + CeIv --+COz + H+ + CelI1 --j r\To3-
(1) (2)
(3)
(5) (6)
+
2Gh-0~ (1) k3 [Cerl'] 1 + __._____ ks [HCOOH] a function of ccrium(II1) concentration, denotes the value of G(CrlI1) a t any particular crrium(111)conrentration in the absence of formic acid. The experimental data were fit to eq I by the method of Irast squarcs using thc computrr program of Lietzkcn Thirteen dcpendrnt variables were determined: the values for GO*, (;NO,, three rate constant ratios listed in Table I, and eight valurs for G(Cexlr)oshown in Figure 2 . Thc exptrimcmtal data adhcre well to cq I as indicated by the theoretical curves in Figure 1 that illustratc the least-squares fit, of the data t o c y I. No better fit of theory to the data could be obtained for any positive value of k-1 [H~O]/(k~[Cc"'I). The Journal
of
Phyaical Chemistry, Vol. 76, N o . 19, 1072
1
0
0.2
0.4
Figure 2. Dependence of G(Ce1'I)0 on [Ce"'] 'I8. Theoretical values obtained by use of eq I to evaluate 13 dependent variables. Line is theoretical and represents least-squares fit of the data to eq I with the assumption that G(CeT")O varies linearly with [Ce"'] 'la.
(4)
We assume that there are primary yields of both OH and SO3 radicals, that>(:OH and G N O are ~ independent of both ccriurn(IX1) and formic acid concentrations, and that reaction 1 is sensibly irreversible. These assumptions togerhcr with the stationary-state hypothesis for OH arid NOs radical concentrations yield eq T. (;(CeJ") = G(Ce'1')"
5.5
Table I: Kinetic Parameters from LeastrSquares Fit of Experimental Data to Eq I Gon GNO3
kdki kdk6
ki[H I' [NO,-I lk4
2 . 0 4 f 0.09 1 56 i 0.12 4 . 1 f 0.9 143 f 11 0 21 I 0 . 0 3 M
Figure 2 shows that G(Cc1IJj0decrcases linrarly with increase in the cube root of thc crriurn(II1) conccntration, to a good approximation, just as previously rcported for sulfuric acid solutions." 2 4 * 2 ( i The expcrimental data were fit by the mcthod of least squarcs t o eq I with the assumption that G(Crl'l)o is zt liricar function of [Ce"']'". G(Cc*ll)o was found to be cqual to (6.40 f 0.04) - (1.4 -f 0.2)[Ce"']''' with thc other kinetic parameters cqual within standard errors to those listed in Table I. We reported in our preliminary c . o m r n ~ n i r a t i o n ~ ~ that GOH is proportional to clrctron fraction watcr in the radiolysis of aqueous nitric acid solutions. This conclusion is based on thrte assumptions. rnt'rgy absorption by water is proportional to rlcctron fraction water; OH radicals result only from rnergy absorption (21) E. J. Hart, J . Amer. Chem. Soc., 74, 4174 (195%). (22) T. J. Sworski, ibid., 77, 1074 (1955). (23) H . E. Spencer and G. K . Rollefson, ibid., 77, 1938 (1055). (24) T. J. Sworski. ibid., 78, 1768 (1956); Radiat. Res., 6, 645 (1957). (25) E. J. Hart, J . Amer. Chem. Soc., 83, 567 (1961). (26) R. W. Matthews, H. A. Mahlman, and T. J. Sworski, J . Phvs. C h a . , 76, 1265 (1972). 9, Ridge Xational Laboratory, (27) M . H. Lietzke, 0 ~ ~ 1 . - 3 2 5 Oak March 21, 1962.
by VF titer; and the fraction of OH radicals that escape by 0.2) X lo2n1-I sec-l for 6.0 M nitric acid solutions with 10 M w&ic acid added.3s cMLtsion from thc spur into the bulk of the solution is Reacttons of NOaRadical in the Spur. T h r formation iailrpendmt of riitr id concentration. LPt ltw dcnotcx ( on fraction water and COHOdeof "molecular" pcroxosulfuric acid arid pc roxodisulfuric acid in the spur was proposed by BoyhiGas cvinote the G valuc f o r OH radical production based upon dence for concurrcnt production of OH and SO4- rad(Anergy absorption hy water. Then G O H O is equal to icals in the radiolysis of aqueous sulfiiric acid solutions. C:olI/li:~. Our v:tluc of GIOH = 2.04 f 0.09 together Vce' substantiated Boylc's proposal b> dctcrminatiorir26 v\Ith EW = 0 '79 yields G ~ =H 2.38 ~ f 0.12 for 4.0 J l nitric acid solutions. 'Phis valuc. of GotIO is equal within of both GOHand (;Isor . By analogy with tht in aqueous sulfuric acid solutions, our tlctc~inination srmidart-l ~ r r o r st o (?o:If = 2.59 f 0.09) the most rerent of both and (:NO, in aqueous 4.0 M nitric acid soluv;ilut* of i : o ~fur~ i.ure water that has been determined tions suggests that reactions of NO, 2 a$ic:il 111 spur 111 our !ahorutory.38 Ii,is also equal within standard should bc of import:mcc 111 aqupoub nitric* n c ~ dsoltierrors to the valuvs for G ' O Jof~ ~2.51 f 0.05 and 2.70 f 0.04 that b ; ~ ~h j l( ~l dcterrmned for 4.0 alld 0.4 M ~ l - tions We previously focuwd attentionJ7J8 on the marked furic wid solutions, r t q ~ t increase in G(ce1Ix)Owith increase in nitrattx ion ronTiic proportionality betsvecn GOEX and EW refutes the centration in 0.4 M sulfuric acid solutions. Thc valuc suggrstionsb that nitrate ion a t high concentrations of (6.40 f 0.05) - (1.4 f O . ~ ) [ C ~ C ~ for ~ ~ JG' '( ~C C " ' ) ~ r ~ a c ~with s P i 2 0f, it cormionly assumed prccursor of in air-saturated 4.0 M nitric acid d u t i o n s is much 3 H radical, tr, yroduc:e thr: BO3 radical with concomilarger than the value2Bof (2.40 0.02) -- (0 74 f 0.06)taut rr Aibltrcxi of OH radical production Our deter[CerI1]"' in air-saturated 0.4 &/r sulfuric acid solutions. m:nat ion of Gzonconfirms t he proposals5,6t11that dircct We have establishedjO that this increase 111 G'(Celll)o intcr:~ction af ratliatrori 'il ith riitratc ion produces the is due to spur reactions that result in iritrous :~,cidproYO, m d suprmcdtbs the previous p r o p 0 s a 1 s ~ ~from J~ duction. There is a concomiinnt Invrcusc in (;('&) our 1ahorstc;ry T h A t dircct interaction of radiation with with this increase in G ( C C ~ I ' ) ~and isotopic. studies nitric acid prorluccs OH and YO2 radicals. have i n d i ~ a t e d two ' ~ sources for this additional o x y g ~:~ i The total ~ i c l t lof oxidizing radicais in nitric acid (I) joint participation of w a t m anti nitratv ion and solutions htts bemi evaiuated prcviously from the en( 3 ) nitrate ion alone. Reactioris of 5 0 3 mdlc:ii 111 thc hanccment iri k;:,CilI") by thallium(X).23~3' In 4.0 spur may be a sourcc: of both nitrous acid and oxygrn 194 nitntt ~olutions,our determination of GOH Combination reactions of ON and SO, radicals jn GPlf)a= 3.6 * 0 2 i;;iii. much better agreement, with the spur may yield three peroxy caoniuouiids. _\lahlmztn's vaiuc of 3 92y than with an interpolated vnluc. of 2.7 from ihc data of Bugaenlco and RoshOH OH --+ H$& (7) c~helctaev."l 'The generztion and reaction kinetics of the NO3 OH KO3 --j- "0, (8, radicni in aqueous solutions were first studied by the flash photolysis of aqueous nitric acid solutions of KO3 so, +K20fl (9) wric nmrnonir;rn nitratc.37sdJ Since further s t ~ c l i e s ' ~ * ~ ~ Hydrogen peroxide is the source of oxygen in the have led to conflicting viewpoints concerning both the radiolysis of cerium(1V) solutions in 0.4 Jf sulfuric gcmmtion arid rcaction kinetics of the YO3 radical, acid solutions. In nitric acid solutions, oxygen may t h e w is 110 firm basis for establishing the validitly of also result from oxidation of both H904 i i r i d I Y 2 0 6 by our value for k Z / , k ) . Our value of 143 f 11 for k 3 / k j cerium(1V). 111 4.0 A I nitric acid boiutioris is not in agreement with reported values'" for k , of (3.7 + 0.1) X lo5 M--l scc-l :tiid k , of (2.06 ir O I ) X IO6 M - ' secw-' in 0.1 J l (28) C. J. Hochanadel and R. Casey, R u d d . Res., 2 5 , 198 (1965). ;YLnCC(NOJ3 solrrliuns. (29) H . A. Mahlman, J. Chem. Phys., 35, 936 (1961). (30) T. J. Sworski, 11. W. Mntthews, and H. A . MahImtm, Advan. This disagreernrnt may only reflect the difference in Chem. Ser., No. 81, 164 (1968). reatction media. 'There is a marked dependence of k3 (31) L. T. Bugaenko and B. M.Roshchektaov, tihiin. V y s . Energ., on nitric acid conwntration with ICs increasing from 5, 472 (1971). (32) T. W. Martin, A. Henshall, and I?. C. Cross, J . Amer. C h m . (3 5.5 -*0.13) >( IO5 1C.l - l scc-l in dilute nitric acid soluSac., 85, 113 (1963). tionb l o about 1.2 X IOG M-' sec-' in 4.0 dl nitric (33) T. W. Martin, R. E. Rummel, and R . (:. Gross. ihid., 86, 2595 (1964). wid solutions. J6 'rhe dcpcndcnct of k5 on nitric acid (34) It. W. Glass nnd T. W-.Martin, ibid., 9 2 , 5084 (1970). cwncrntrat ion hiLb not been detcrmined, but it may (35) T. W. Martin and It. W. Glass, ibid., 9 2 , 5075 (1970). dccrwse ~ v r t h incrcaw in nitric acid concentration (36) J. W. Boyle, Radint. Res., 17, 427 (1962). sinccl the absolute r;atc. eonstant for reaction of NO3 (37) T. J. Swonki, J . Amer. Chem. Soc., 77, 4689 (1955). radicd with act%ic :tcid decreases from (4.6 f 0.4) X (38) H. A. Mahlman, J . Phya. C h m . , 61, 1598 (1960). IO4 14-1sec-1 in 0. L IiP KsCe(NOs), solutions10to (2.3 f (39) H. A. Mahlrnan. ibid., 67, 1466 (1963). t h c b
*
+
+ + +
The Journal of Ph,y&al Chemistry, Val. 76, 1Vo. 19, 1972
R. W. MATTHEWS, H. A. MAHLMAN, AND T. J. SWORSKI
2684 CeIV &IV
+ HNO, +CelI1 + H+ + 0, + NOz
4- N2O6 -* '2e"' 4- NO2+
0 2
(10)
NO7 (11)
Glass and Martina4 have proposed the sequence of reactions 9 and 11 for the net reduction of cerium(1V) in the photolysis of ceric ammonium nitrate in nitric acid solutions. We have no evidence that either HNOa or N2Oe arc sufficiently long lived for reactions 10 and 11 to be significant. Both HXOd and N208 may well be unstable intermediates that decompose rapidly t o yield nitrous acid and oxygen.
+ HNOz +02 + 2N02
HNO, +0 K206
2
(12) (13)
Reaction 12 ha8 been suggested to occur in the photolysis of alkaline nitrate solutions.@ The oxygen resulting from intermediate formation of NzOawould have nitrate ion alone as the source. The oxygen resulting from intermediate formation of "0, would have joint participation of nitrate ion and watcr as the source. Since NOz does not react with either cwium(1V) or cerium(II1) ions,3o nitrous acid would result, from production of NO? by reactions 10 and 11. We cannot, determine the importance of "0, and N206production in the spur since further contributions to nitrous w i d and oxygen production may result from excited states of nitrate ion. Although the
The Journal of Physical Chemistry, Vol. 76,N o . 19, 1978
photolysis of aqueous nitric acid solutions does not produce the NO3 radical,34nitrite ion and molecular oxygen do result from excitation of nitrate ion both in tho lowintensity band a t 3 0 0 nmro and in t'he intense band a t 201 nm.41,42 Excited stat,es of nitrate ion r~lsoyield NOz and OH radical pairs, most, of which undergo geminate recombination when produced photochemically. These radical pairs in the spur? however, may result in increased yields of hydrogen peroxide containing oxygen from nitrate ion.! originally attrib~ t e tod reactions ~ ~ of NOI radical witth watcr. I n the radiolysis of concentrated nitrate solutions, excited states of nitrate ion most, certainly would result from direct interaction of radiation with nitrate species in solution and may also result from int,oractjion of nitrate ion with excited states of n-:iter.37'44Although it has long been established that chemical reactions can be induced by photoactivut,ion of 1vatcr,45,46 the role of excited s t a h in the radiolysis of aqueous solutions has not yet been established. (40) M. Daniels, li. V. Meyen, and E. V. Belardo, J . P h y s . Chrna., 72,389 (1968). (41) U. Shuali, M. Ottolenghi, J. Itsbani, and 2. Yelin, ihid., 73, 3445 (1969). (42) F. Barat, L. Gales, B. Hickel, and J . Sutton, J~ Chem. Soc. A , 1982 (19iO). (43) M. Faraggi, D. Zehavi, and M. Anbar, Yrana. Faraday L%c., 67, 701 (1971). (44) T.J. Swomki, Advan. C h m . Ser., No. 50, 263 (1965). (45) H.Fricke and E. J. Hart, J . Chem. Phys., 4, 418 (1936). (46) J. Barrett and J. H. Baxendale, T r a m . Faraday Soc., 56, 37 (1960).
