Chem. Rev. I @ W 87, , 513-534
513
Electron Affinities and Electron-Transfer Reactions PAUL KEBARE’ and SWAPAN CHOWDHURY Chemkfry D # p ” n t ,
unlversl?. O f Alberte. Edmonton, Alba~ta.Cane&. T6G 2G2 R e c e M Jenuery 8. 1987 (Revised h4anuscript Received February 17. 1987)
Contents I. Introduction 11. Determination of Electron-Transfer Equilibria
513 515
and Electron Affinities
111. Kinetics of Electron-Transfer Reactions 1:
+
+
B=A BAIV. Electron Affinities: Structures and Stabilities of Radical Anions A. Substituted Aromatic Compounds B. Substituted Benzw. Naphtho-. and Anthraquinones C. Hexafluorobenzene. Substituted Perfluorobenzenes. SF,. and Perfiuorocycloalkanas D. Triatomic MoIecuIes, Tetracyanoethylene, and Miscellaneous Compounds V. Entropy Changes on Electron Attachment.
517 519 519 521 524
525 525
AS,O
VI. Solvation Energies of Anions A- and Binding Energies in A--B CMnplexes A. Soivatkm Energies of Anions from Polarographic Half-Wave Potentials. Relationship to Gas-Phase Solvation B. Binding Energies in A-.SI Complexes C. Binding Energies in A-43 Complexes VII. Thermal Stability of Anions: Electron Attachment and Detachment at Thermal Energies VIII. Relevance of Data to Analytical Mass Spectrometry
526 526
527 528 530
Paul Kebarie was b a n in Sofia, Bulgaria. He studied chemistry at EM h Zvich,S*erland, and took his Ph.D. in Physical Chemistry (reaction kinetics) at the University of British Columbia in Vanwwer. After 2 years postdoaaai wcik wim Fred Lossing at NRC Ottawa he joined the academic staff at the Chemistry Department of the University of Alberta in 1958. Studies of ions in gases near atmospheric pessues in his iabwatay in 1964 led to ttm discovery that ion-molecule equilibria occur Spontaneously at higher pressures and can be measured under these condiiions. His research since that time has been devoted to the study of ion-molecule reaction equilibria and the application of the data in various areas of chemistry.
531
I . Introduction T h e electron affiiities of molecules are o f interest not only in areas where gas-phase ions are encountered, e.g., negativeion analytical mass spectrometry,’” gas-phase
radiation chemistry! ionosphere: gaseous electronics,8 electron capture detector gas chromatography,”l’ and gas-phase i o n chemistry,’* but also in the m u c h wider field o f condensed-phase chemistry. Charge-transfer complexes a n d t h e i r role in organic, biological, a n d catalytic processes represent a n example o f a vast condensed-phase area for which knowledge of electron affinities i s of p r i m e importance.’618 E v e n m o r e important is the role o f electron transfer in biological redox p r o c e ~ s e s . ’ ~Rich,I3 C h r i s t o p h ~ r o u , ’ ~S ~ w a r c , ’ ~a n d BierglebI6have discussed the significance o f electron affinity to these areas. Eberson” has recently considered the possible relationships between dissociative electron transfer and t o x i c i t y o f t h e compounds involved in dissociative electron transfer. Single-electron-transfer reactions in solution belong to a major research area in inorganic chemistry.I8 Reductions through single-electron transfer f r o m alkali metals to unsaturatedorganic compounds, e.g., Bouveault-Blanc 000~2665/87/0767-0513$06.50/0
Swapan Chowdhuy was ban h Chitlagong. Bangladesh. He obtained his B. Sc. (Honors) and M. Sc. degrees in Chemistry from the University of Chiwagong. Very recently he received his Ph.D. degree from ttm Universky of Alberta. where he worked under the direction of Professor Paul Kebarie. Currently he is doing p s t doctoral research, involving tendem mass spectrometry. with Professor Alex. Harrison at the University of Taonto. His research interests are in ttm general area of mass spectrometry wim special emphasis on analytical techniques, such as chemical ionization (Ci). collision-induced dissochtion (CID). and fast-atom bombardment (FAB)
and B i r c h reductions, have been o f importance in synthetic organic chemistry for a number of years. Furthermore, some reactions t h a t were previously consid-
0 1987 Amerlcan Chemlcal Society
514 Chemical Reviews, 1987, Vol. 87, No. 3
Kebarle and Chowdhury
ered to be of the SN2type have now been reinterpreted The corresponding enthalpy can be obtained via van't on the basis of single-electron-transfermechanism^.'^ Hoff plots of Kl measured at different temperatures or In all these solution reactions, the stabilities of the from extrathermodynamic estimates of AS,', the entropy changes, which are generally quite small. A series anions are of prime importance, and these depend on the gas-phase electron affinity and on the solvation of interconnected equilibria is measured such that a energy of the anion. continuous AG1' and AHl' scale (ladder) is obtained. Since the electron affinity (EA) is such an important Absolute electron affinities (eq 4-6) are obtained by fundamental property, it is not surprising that many calibrating the scale to the known, literature, electron methods for EA determination have been used. Thus affinity of one or more of the participating compounds. in a 220-page recent review of electron affinities by These compounds are the external standards or Christophorou,20some 31 different methods for electron "anchors" of the scale. The technique and procedures are described in more detail in section I1 of this article. affinity determinations are described. In spite of the availability of a large number of methods and the funFukuda and McIver,31-34using a pulsed ICR, were the damental importance of EA values, data are not first investigators to measure equilibria 1. The comavailable for many molecules of interest,20and when pounds A and B involved were mostly singlet molecules data are available, there can be very significant dissuch that electron capture led to doublet radical anions. agreement between different determinatiom2O Unfortunately, due to a faulty determination of the EA Two other recent reviews of electron affinities are by of SO2and nitroben~ene,~~ these authors anchored the Lineberger21and Brauman22(see also papers by these electron affinity scale i n ~ o r r e c t l y . Extensive ~ ~ , ~ ~ meaauthors in this issue). The electron photodetachment surements of equilibria l from the reviewers' laboratory studies described by these authors represent the most were initiated in 1983. The method proved to be very accurate methods for EA determination. For diatomic efficient and relatively straightforward. This allowed and small polyatomic molecules where the photodethe determination of the electron affinities of some 120 tachment spectrum can be resolved, i.e., where the incompounds up to the present time.36-47 itial and final states involved in the transitions can be All compounds involved were stable molecules with identified, one obtains not only EA but also vibrational positive electron affinities. The vast majority were spacings in the neutral molecule and the negative ion. singlet molecules which on electron capture became However, when polyatomic molecules are involved and radical anions. the geometry of the negative ion and the neutral are The measurement of the electron-transfer equilibria quite different, resolution of the spectra may be diffi(ETE) almost automatically leads also to a study of the cult. The problem may be further aggravated when kinetics of the electron-transfer reactions (eq 1). The internal excitation is present in the negative ion (hot rate constants of some 90 electron-transfer reactions bands). The photodetachment spectrum in such cases were determined.37-43,45,46 Exothermic ion-molecule may be so complicated that an electron affinity deterreactions in the gas phase often proceed at collision mination cannot be obtained. rates, and this was found also to be the case for electron Gas-phase ion-molecule equilibria measurements, transfer. Collision rate constants provide little inforfirst developed and demonstrated in this l a b ~ r a t o r y ~ ~ .mation ~~ on the details of the electron-transfer process. with a pulsed electron high ion source pressure mass More interesting are exothermic electron-transfer respectrometer (PHPMS) (see Figures 1 and 2) and later actions which proceed with rates that are lower than also executed in an ion cyclotron25and flowing afterglow collision rates. The slow rates generally reveal the appratuses,26 have proven to be an extraordinarily magnitude of the energy barrier for the electron-transfer prolific source of ion thermochemical data such as process. The kinetic results and discussion are given ion-ligand binding e n e r g i e ~ ,proton ~ ~ , ~ ~affinities of in section I11 of this paper. neutrals (gas-phase basicities) and negative ions (gasTypically, organic compounds with positive electron phase a c i d i t i e ~ ) and , ~ ~ hydride ? ~ ~ and chloride affinities affinities possess conjugated bonds, and this leads to of c a r b o c a t i ~ n s . ~ ~ a relatively low-lying lowest unoccupied molecular (T*) Relative electron affinities can also be determined orbital (LUMO), which accepts the extra electron and with the ion-molecule equilibrium technique. The becomes the singly occupied molecular orbital (SOMO). equilibria involved are given in eq 1. In addition to conjugation, the presence of electronegative atoms or electron-withdrawing groups (F, C1, A-+ B = A + B(1) CHO, CN, NO2) leads to lowering of the LUMO energy and thus to a higher electron affinity. The compounds whose EA'Swere determined were substituted benzenes, naphthalenes, anthracenes, substituted quinones, perAG1' = -RT In K1 = AH,' - TASlo fluorinated systems like C6F6and SF,, perfluorocyclo(3) alkanes, and some smaller molecules like SO,, NOz, and e+B=B(4) CH3N02. The results of the electron affinity determinations A H 4 ' = AHao(B) AG,' = AG,'(B) (5) and relationships between structure and stability of the AH,' = AHao(B)- AH,'(A) (6) anions are examined in section IV of this paper. The measured entropy changes on electron attach-EA(B) zz AHao(B) (7) ment AS,' can in certain cases provide useful information on the structural changes occurring on formaThe equilibrium constant K,, given in eq 2, is detion of the negative ion. These results are discussed in termined by the experimental measurement. One obsection V. tains the electron-transfer free energy AGIO from eq 3.
Electron Aninlies and Electron-Transfer Reactions
The electron-transfer reactions in the gas phase may proceed via relatively long-lived adduct complexes A-.B. In some cases the adduct complexes can be stabilized by collisions with a third gas, and the equilibria (eq 8) can be measured. A- B = A-.B (8)
+
Such measurements lead to determinations of the binding energies AGE0 and enthalpies AHE. of the adduct A-.B. The binding energies may indicate characteristic binding between the anion and the molecule, i.e., hydrogen bonding or covalent bonding as in Meisenheimer complexes. Furthermore, the bonding in A-.B may be of importance to the kinetics of the electron-transfer reaction. These results and discussion are given in section VI. As mentioned above, radical anions are important species in solution. The available gas-phase electron affiiities can be compared with energy data in solution. Most useful in this respect are the polarographic halfwave reduction potentials E l / 2 Combination of the gas-phase data with the solutton reduction potentials leads to evaluations of the solvation energies of the radical anions. Additional insight into the nature of the solvation interactions can be obtained by measurement of the gas-phase ion-molecule equilibria 9, where B- is B- + SI = B-.SI B-(SI)n-l + SI =B-(Sl), (9) a given anion and SI is a molecule of a solvent vapor like methanol, acetonitrile, or dimethylformamide. These data and discussion are also presented in section VI of this paper. The formation of negative ions B- in the presence of B and thermal electrons depends on the temperature and pressure and the internal properties of B and B-. More directly, the observation of B- depends on the values of the electron thermal attachment and detachment rate constants. These relationships are discussed in section VII. Negative ions play an important part in analytical mass spectrometry. Particularly important areas are chemical ionization (NICI), fast atom bombardment (NIFAB), thermospray, and electrospray. The relevance of the PHPMS results to these fields is discussed in section VIII. The literature coverage in this article restricts itself to gas-phase electron-transfer reactions and equilibria and electron affinities derived therefrom. Most of this work is contained in ref 31-47. Other literature is covered only insofar as it relates to the data obtained from electron-transfer equilibria and the kinetics studies. The literature coverage extends to September 1986.
I I . Detennlnation of Electron-Transfer Equlllbria (ETE) and Electron Affinities(EAs) The electron-transfer equilibria (eq 1) were measured in the laboratory of the reviewers with the pulsed electron beam high ion source pressure masa spectrometer4' (PHPMS) used in earlier ~ o r k . 2The ~ pulsed electron, ion source (see Figure 1)contains typically 5 Torr of bath gas, most often methane, and millitorr pressures of compounds A and B. A short -10-ps pulse of electrons accelerated by 2000 Venters the ion source through a very narrow slit and leads to production of
Chemical Reviews, 1987, voi. 87, NO. 3 515
I vsmm
lo".
Io miss aluly.is
Figure 1. Ion source of pulsed electron high pressure mass spectrometer PHPMS. Relatively high bath gas pressure (5 Torr) traps ions since it slows diffusion of ions to walls. Also,high bath gas pressure lead8 to thermal reaction conditions.
6 Figure 2. PHPMS apparatus: (1) pulsed electron gun: (2) temperatureeontrolled ion source: (3) open cage d e f h g electrical field; (4) heating and cooling mantle; (5) accelerating electrodes; ( 6 ) to magnetic mass analysis tube; (7) slow in and out flow of reaction mixture through ion source; (8)6in. differential pumpinp; (9)4-in. differential pumping.
positive ions and secondary electrons by electron impact with the bath gas. The secondary electrons am brought to near thermal energies by collisions with the bath gas. Electron capture by A and B leads to excited (A-)* and (B-)*, which are subsequently thermalized by collisions with the bath gas. As A- and B- diffuse toward the walls they engage also in electron transfer with neutral B and A molecules, and the electron-transfer equilibrium (eq 1) is achieved under suitably selected conditions. The ions coming to the vicinity of the very narrow ion exit slit escape into the vacuum chamber where they are accelerated,mass analyzed, and detected (see Figure 2). The time between pulses is typically 10 ms. One given mass is observed over some 500010000 pulses, the accumulated signal leading to better signal-to-noise ratio. The ions arriving at the ion detector after the electron pulse are counted and the counts stored in a multiscaler as a function of time." Ion intensities obtained in typical experiments3' are shown in Figure 3. Electron capture by A and B leads
516 Chemical Reviews, 1987, Vol. 87, No. 3
z'
Kebarle and Chowdhury
I
,04
Compounds
A
2.3-CI2Np0 3.5-(N02)2eN 4-NOZNB BO NPQ W 2 ' '
AH:^
AH: kcrllmol
kcrl/mof02
4-CNNB 3-CNNB 37
MaAn
4-CINB
.
07
iol;
"
*
"
05
"
"
"
"
10
"
3G:, (423)o
4-CNNB 3-N02NB 2-CNNB
- SG;,so,
-3G: (423K)+O 1 (423Kj (kcal/molj
1111
t 126
38 7
so2 F5BN
'IF14 sF6
20
I
36 9
97
35 8
5.5
31 6
246
49 8
20 8 18 9
46 0 44 1
16 5
41 7
14 3
39 5
10 9
36 1
76
32 8
71
32 3
37
28 9
29
28 1
I
I
0
25.2
-0 3
24 9
-0.5
24 7
-1.6
23.6
5.2 1.8
1
23.0 -3.9
E
21.3
16.8
-13.2 d'4
12 0
F i g u r e 5. Partial AH1'' scale based on van't Hoff plots of equilibrium constants K , for electron-transfer reaction 1: A- + B = A B-. Also given are AHet(S02)values corresponding to AH for the reaction SOz- A = SO2 A-. Absolute AH, corresponding to e + A = A- are obtained by calibration to literature EA(S02). From C h ~ w d h u r y . ~ ~
+
+
+
3-FN
NB
22 s
-33
F i g u r e 4. Partial ladder (scale) giving values for AGIO = AGet for the electron-transfer equilibria A- B = A B-. These AGO values can be combined to provide AGeto(S02) for the reaction SOz- A = SOz A-. Known AG,"(S02) = -26.1 kcal/mol evaluated from literature data leads to AG,"(A) for all of the other compounds. AG,"(A) corresponds to the reaction A + e = A-. Scale illustrates connections to the standard SOz. NB stands for nitrobenzene. The subscript a in AG," stands for attachment process (eq 4).
+
+
I
Z-CHjNB
10 8
C6F6
I
1
50 7
NB
AZ
3-CF3NB
*
I 2.2
53
1
I
25 5
70
20
I5
Time (milliseconds) F i g u r e 3. Observed37ion intensities after 1 0 - k ~electron pulse. In B, a kinetic stage precedes achievement of electron-transfer equilibrium, while in A the equilibrium is established rapidly. kcal/mol
37
3-FNB
"
kcrllmol
6.8
33
3-CFSNB I
-AH;- EA
+
+
to formation of A- and B- (Figure 3B). However, due to the higher electron affinity of the dichloronaphthoquinone (B),the intensity of B- is seen to increase with time while that of A- decreases. After some 0.7 ms, the intensity ratio B- to A- becomes constant with time, which for the logarithmic intensity plot used corresponds to a constant vertical distance between B- and A-. The constant ratio is assumed to be due to achievement of equilibrium 1. In Figure 3A conditions are such that the equilibrium is established much faster. In both A and B the linear decrease of the log ion intensities after equilibrium has been reached is due to first-order diffusion and destruction of the ions at the
wall of the ion source. The ion intensity ratio after equilibrium is achieved is substituted into the equilibrium constant equation (eq 2). The concentrations of the neutrals A and B are known from the original composition of the mixture. Ion formation is a minor process, so that [A] and [B] remain virtually unchanged. A ladder (scale) constructed from AG," values obtained from some of the electron-transfer equilibria is shown in Figure 4. Determinations of K , at different temperatures lead to the evaluation of AH,"and AS,' via van't Hoff plots (see eq 2 and 3). Thus, one can also construct AH,"and AS," ladder^.^^-^^ Partial AH," and AS," ladders are given in Figures 5 and 6 . The electron affinities of the compounds in the AH,' ladder are evaluated4, from the electron affinity of SO2 determined with the electron photodetachment method by Hall.49 Furthermore, there are other electron affinity values for SO2, within f O . l eV of Hall's value: 1.097 f 0.036 eV. SO2 is a good standard also because the geometries and vibrational frequencies of SO2 and SO2- are available from the literature (see Table I, ref 41). The photodetachment electron affinity49corresponds to the negative energy change for the electron attachment process (eq 10) where SOz and SO2-are in their SO2 + e = SO,-
AH,(S02)
(10)
ground electronic, vibrational, and rotational states. By use of the stationary convention for the
Electron Affinities and Electron-Transfer Reactions
Chemical Reviews, 1987, Vol. 87, No. 3 517
of the electron-transfer cross s e ~ t i o n This . ~ ~ work ~~~ established that the conversion of translational energy int~ internal (electronic) energy is a relatively inefficient process. The largest cross sections are occurring for resonant processes, i.e., for cases where the recombination energy of A’ matched the ionization energy of 15 7 B, at near zero relative velocities. For brief reviews see 15 0 10.0 FutrelP and L i n d h ~ l m . ~ ~ Early qualitative extensions of the theory based on experimental findings for diatomic systems and thermal rate constants were published by B ~ h m and e ~ Bow~ e r ~ These . ~ ~ and earlier authors emphasized the importance of “accidental” resonance for molecular systems. Accidental resonance is achieved by transitions to electronically and vibrationally excited states whose density might be quite high for molecules. Since the transition from A+.B to A.B+ involves a fast electron jump, the transitions are vertical, i.e., the internuclear distances in the molecules A and molecules B are, from I I I I I I I I I --SO2 00 a classical view point, preserved, or, quantum meT I T T I4 7 I I I I I I I I ,&o chanically, the transition probability is governed by the Franck-Condon factors. Implicit in these treatments is also the assumption of weak electronic overlap be-2 5 tween A+ and B in A+.B and A and B+ in A.B+, where 40 -3 2 A+-Band A.B+ are the complexes just before and after -3 6 -3 7 the electron jump. -40 -45 A systematic experimental and theoretical develop-47 -5 2 ment concerning the rate constants of electron-transfer -5 61 reactions involving polyatomic molecules does not seem -61 to have occurred. For a brief discussion and leading 4 5 references see the Introduction in McEwen.60 It has been recognized that for electron-transfer reactions the 0 2 e N 0 2 classical spiralling collision rate constant (LangevinAD0)61p62need not be the upper limit. In cases where Figure 6. Partial A s l o scale based on van’t Hoff plots of equilibrium constantsKl for the reactions A- + B = A + B-.From energy resonance is present and the Franck-Condon these, hseto(S02) corresponding to the reaction SO, + A = SO2 factors are very favorable, the electron jump may occur + A- is derived. ASa0 corresponding to the reaction A + e = Ain the “fly by” at distances larger than those correis derived from literature data for AS,(SO,). From Chowdhury.4l sponding to the classical orbiting limit, although firm Subscript a stands for attachment process (eq 4). experimental evidence for the occurrences of such large EA(S02)corresponds to the -AHa(S02)at 0 K. AHarate constants does not seem to be availablee60 The (SOz) at 298 K can be evaluated41 from the available majority of thermal exothermic electron-transfer reacvibrational frequencies of SO2and SO2-and EA(S0z).49 tions involving polyatomic reactants occur at near Due to the similarities of SOz and SOz-, AHa’ at 298 and collision limit rates. 0 K are found to differ by only 0.1 kcal/mol, a differRelatively few determinations of thermal rate conence that is smaller than the expected error of the AHl’ stants for the electron-transfer reactions (eq 1)involving measurements. negative ions have been reported.'^^^-^^-^^+^ Most of these s t ~ d i e were s ~performed ~ ~ ~ ~primarily ~ ~ ~for~ the AHa(SOZ),, = -EA(SOZ) + 0.1 kcal/mol determination of electron affinities via (l),where, inElectron attachment entropies for SO,, ASao(SOz),can stead of measuring the equilibrium (eq l),one measures also be evaluated from the available frequencies and rates (bracketing method). The assumption is made g e ~ m e t r i e s .Thus ~ ~ SO2serves also as an anchor in the that if the reaction is exothermic it will proceed at near entropy as well as free energy ladder (see Figures 4-6). collision rates.65 Systematic determinations of thermal rate constants I I I . Klnetlcs of Electron- Transfer Reactions 1: kl were undertaken in the reviewers’ laboratory from A - 4- B = A B1984 onward.37*36*40~4z-G A description of the method of measurement is given in G r i m ~ r u d .Some ~ ~ 90 rate Electron transfer (1) involving negative ions in its constants were determined. Part of these are summaessential features is analogous to electron transfer inrized in Table I. volving positive ions (eq 11). Reactions 1 or 11 are Exothermic electron transfer between NOz, SOz, A+ + B = A + B+ (11) substituted benzenes, perfluoroaromatics, quinones, naphthalenes, anthracenes, and azulene was found to often referred to as charge-transfer reactions by workers proceed at near collision rates. In most cases (see Table in the gas phase. Electron-transfer reactions have been much studied both in the gas phase and in s o l u t i ~ n . ~ ~ J IA), ~ the rate constants predicted by ADO theorf2 were found to be in good agreement with the experimental Early theoretical work involving gaseous atomic ions determinations. and neutral atoms dealt with the velocity dependence
F
I 16301“1I I I I I I I I IGT?
+
518 Chemical Reviews, 1987, Vol. 87, No. 3
Kebarle and Chowdhury
TABLE I (A). Rate Constants for Exothermic Electron-Transfer Reactions 1: A- + B = A A"
B" p-NOzNB m-NOZNB P-NO~NB m-NOZNB m-CFSNB m-Cf,NB NO2 NO2 NO2 NO2
NB NB m-CF3NB p-FNB NB p-MeNB NB p-CHBNB p-ClNB n-NO2NB
1 2 3 4 5 6 7
8 9 10
kl(exptl)b 1.3 2.1 1.3 1.9 1.8 1.9 0.4 0.5 0.5 0.5
kl(ADO)C 1.1 1.8 1.0 1.8 1.8 1.7 0.6 0.6 0.6 0.6
11 12 13 14 15 16 17 18 l9 2o
(B). Exothermic Electron Transfer Rate Constants k for AA B -AH0 SF6 3-CF3C6H,NO2 8.9 SF, 3-NOzC6H4NOz 14.5 SF6 4-CNCsH4NOz 15.5 SF6 4-NOzC6HdNO2 22.5 SF6 FlCBOZ 38.6 CF3C6F11 3-CF&H4NOz 7.7 CF3C6F11 3-NO2CsH4NOz 13.3 CF3C6F11 4-CNCeH4NO2 14.6 CF3C6F11 4-NOzC6H4NO2 21.3 CF3C6F11 2,6-C12C6H202 32.3 CF3C6F11 F4C602 37.4
A" P-NO~NB BQ azulene p-FNB P-NOZNB p-NOZNB 2,3-ClZNpQ 2,6-C12BQ C7F14
-
C7F14
+B
B" NO2 NO2 m-CF3NB BQ 2,6-C12BQ 2,3-C1zNpQ 2,6-ClzBQ Cl4BQ 2,6-ClzBQ NO2
+ Bkl(exptl)b 0.4 0.3 1.0 1.4 1.0 0.4 1.5 0.5 0.8 0.08
kl(ADO)C 0.6 0.5
A + B- Involving SF6 and C7Fl4at 423 K k(obsd)'vf EVE llPh 5 x 10-18 6.9 7.4 6 X lo-" 6.0 5.4 1.0 x 10-10 4.3 4.8 1.0 x 10% 3.0 2.9 1.4 X 10% 0.0 0.3
