2458
Peterson et al.
The Journal of Physical Chemistry, Vol, 83, No. 19, 1979
position block hydrogen bonding with amines. Phenols with alkyl substituents at both the 2 and 6 positions were divided by Stillson et a1.16 into two groups: hindered phenols and cryptophenols. The hindered phenols were described as insoluble in water and aqueous alkali, as sparingly soluble in alcoholic alkali, as unreactive with either aqueous alcoholic Fe3+ or with sodium in anhydrous petroleum ether or diethyl ether, and an unable to esterify with acetic acid or benzoic acid by conventional ester forming reactions. These hindered phenols have large groups such as tert-butyl or tert-amyl in the ortho position. Partly hindered cryptophenols were described as being water insoluble and sparingly soluble in aqueous alkali, but as displaying phenol-type reactivity otherwise. Coggeshall17reported that, at high concentration, hindered phenols formed only very weak hydrogen bonds with one another, while crytophenols were intermediate in bond forming ability between hindered and unhindered phenols as evidenced by the shift in the hydroxyl infrared band a t 2.7 pm. It would appear that amines are more readily blocked in their approach to the phenol hydroxyl to form a hydrogen bond than are reactants in any of the above reactions. Even o-methyl groups prevent phenol-amine hydrogen bond formation. By contrast o-methyl groups have only a small effect on phenol-phenol hydrogen bond formation. In assessing the importance of a single ortho substitution, we find that comparison of the results, amine by amine, for the interaction of phenols of similar acid strength and no ortho substituent @-cresol), a small ortho substituent (0-cresol), and a more bulky ortho substituent (0-sec-butylphenol) reveals no significant difference in reactivity as measured by the equilibrium constant for hydrogen bond formation (Tables I and 11). Presumably,
the amine approaches the phenol at an angle that causes it to occupy the same position as would even a very small ortho substituent, but that this causes a problem only when both of the positions are substituted. Finally, these data provide repeated confirmation of the relative difficulty experienced by tertiary amines in hydrogen bonding to a phenol.
Summary The formation of hydrogen bonds between mono- and di-ortho-substituted phenols and aliphatic amines is studied. The results support the proposal that tertiary aliphatic amines are sterically hindered in this reaction. The presence of two ortho groups on the phenol prevents any hydrogen bond formation with amines, while a single ortho group has no effect on such a reaction. References and Notes (1) R. A. Morton and A. L. Stubbs, J . Chem. Soc., 1347 (1940). (2) A. Burawoy and I. Markowitsch-Burawoy,J. Chem. Soc., 36 (1936). (3) A. Burawoy and J. T. Chamberlain, J. Chem. Soc., 2310 (1952). (4) A. Burawoy and J. T. Chamberlain, J . Chem. Soc., 3734 (1952). (5) S.Nagakura and H. Bada, J . Am. Chem. Soc., 74, 5693 (1952). (6) S.Nagakura, J. Am. Chem. Soc., 76, 3070 (1954). (7) L. Bellon, C. R . Acad. Scl., 254, 3346 (1962).
(8) R. A. Hudson, R. M. Scott, and S. N. Vinogradov, Spectmhlm. Acta, Part A , 26, 337 (1970). (9) L. Bellon, Trav. Inst. Sci. Cherifien Ser. Sci. Phys., No. 6 (1960). (10) M. Bonnet and A. Julg, J . Chem. Phys., 59, 723 (1962). (11) N. S.Coggeshall and E. M. Lang, J . Am. Chem. Soc., 70, 3263
(1948). (12) S.Nagakura and M. Gouterman, J. Chem. Phys., 26, 881 (1957). (13) M. Lin and R. M. Scott, J . Phys. Chem., 76, 587 (1972). (14) N. J. Rose and R. S. Drago, J. Am. Chem. Soc., 81,6138 (1959). (15) M. D. Young, “Statistical Treatment of Experimental Data”, McGraw-Hill, New York, 1962. (16) G. M. Stillson, D. W. Sawyer, and C. K. Hunt, J . Am. Chem. Soc., 67, 303 (1945). (17) N. D. Coggeshall, J . Am. Chem. Soc., 69, 1620 (1947).
A Radioisotope Labeling Technique for Vapor Density Measurements of Volatile Inorganic Speciest E. J. Peterson,* J. A. Calrd,t Jan P. Hessler, H. R. Hoekstra, and C. W. Willlams Chemistry Division, Argonne National Laboratory, Argonne, flllnois 60439 (Received April 27, 1979) Publication costs assisted by Argonne National Laboratory
A new method for complexed metal ion vapor density measurement involving labeling the metal ions of interest with a radioactive isotope is described. The isotope chosen in the present work is unstable and leads to emission of a characteristic y ray. Thus the y-counting rate was related to the number density of complexed metal ions in the vapor phase. This technique is applicable to the study of any volatile inorganic species, but in the present study has been used to measure vapor densities of complex species in the TbCl3-A1Cl8system by using tracer 160Tb.
Introduction The study of high temperature vapors has practical application in a variety of metallurgical processes, in the understanding of unique properties of vapor deposited single crystals and in synthetic procedures which utilize vapor species as reactants.l Generation of volatile metal t Work done under the auspices of the Office of Basic Energy Sciences of the Department of Energy. Bechtel National, Inc., San Francisco, CA 94119.
*
0022-3654/79/2083-2458$01 .OO/O
containing compounds can be accomplished in an intermediate temperature regime by addition of a complexing agent (e.g., group IIIB metal halides) to a metal halide system thus forming volatile complex species.2 The recent suggestion of Krupke3 that LnC13(A1C13),vapor complexes (where Ln = lanthanide) be considered as possible energy storage media for high power optical gain systems has encouraged examination of the chemical and optical properties of these s y ~ t e m s . ~In - ~analyzing the optical properties it is necessary to understand the nature and 0 1979 American
Chemical Society
Vapor Density Measurements of Volatile Inorganic Species
thermodynamic stability of the complex vapor species. The reaction for complex formation in LnCI3(AlCl3), systems, which is responsible for increased vapor phase lanthanide ion concentration with respect to the partial pressures of the pure lanthanide halides, can be written LnCls(s,k) -I-nA1zCl6(g) -F! LnAlz,C&,+a(g) (1) From a knowledge of the temperature-dependent vapor densities of complexed lanthanide ions and the partial pressure of aluminum chloride dimer, which can be calculated from published datas if the molar concentration of A1C13(s) is known, the composition of the vapor phase can be inferred and the equilibrium concentrations of the vapor species may be c a l c ~ l a t e d . ~ J ~ Both direct and indirect methods of complexed metal ion density measurements have been used in the derivation of thermodynamic parameters in previous investigations of vapor complex systems.ll Of these methods, the spectrophotometric technique has been the only method used for measurement of lanthanide and actinide complexed metal ion den~ities.~ The information obtained by this method is actually the product of the vapor density of complexed metal ions and the oscillator strength as shown in the following equation?
where 1 is the optical path length, A(") is the observed optical absorbance, e and m are the charge and mass of the electron, respectively, c is the velocity of light, p_rt is the vapor density of the nth complexed species, and f n is the average oscillator strength of the nth complexed species for transitions between two J manifolds. Because the spectrophotometric technique measures the product of the complexed metal ion density and the oscillator strength, it is necessary to make two assumptions about the system in order to extract vapor density data. The oscillator strengths of the various species must be independent of temperature and the relative complexed metal ion densities for saturated and unsaturated systems (with respect to metal halide) must be identical. To test the validity of these assumptions implicit in the spectrophotometric experiment and to provide data when the optical method is not applicable, a radioactive tracer technique, which is sensitive only to the vapor density of complexed metal ions, was developed. The radioactive experiment monitors the y-ray count from a portion of the vapor, which is related to the complexed metal ion density through the specific activity of the tracer. No assumptions are necessary to relate the experimentally measured y count rate to the complexed metal ion density. It will be shown that the accuracy and precision of the data are superior to data obtained by optical experiments. The radioactive method is also applicable to systems which are not amenable to study by the spectrophotometric technique. In situations where both techniques can be used, complementary data will be available to aid in characterization of the vapor system. The tracer method was used to examine the TbCl,(AlCl,), system, where the characteristically weak (spin-forbidden f f) absorption bands of Tb3+limit the accuracy of the optical measurements.
-
Technique Description This method of complexed metal ion density measurement is based upon the utilization of relatively short half-life radioactive tracers which lead to the emission of y radiation. For experimental simplicity it is desirable that the y ray energy be greater than 0.4 MeV. To explicitly
The Journal of Physical Chemistry, Vol. 83, No. 19, 1979 2459
state the important parameters of the technique, the probability per unit time for the detection of a y ray of energy E, P(E),is written
The complexed metal ion density in the vapor a t position 7 is p(?), the fraction of the radioactive tracer at the time of the measurement is f ( t ) ,the detector efficiency is €(E), and I,,(E) is the probability per unit time for the emission d E = (In 2)/TIl2. The of a y ray of energy E. SOmZy(E) time dependence of the fraction of radioactive metal ions is given by f ( t ) = foe-('" Z)t/Tl/z
(4) where fo is the initial fraction of the radioactive tracer, t is the time after production of the radioactive tracer, and Tl/zis the half-life of the radioactive tracer. The solid angle integration is over the angles defined by the detector and lead shielding, which is a function of 7. If the sample dimensions are small with respect to the distance to the detector, the integration over the solid angle can be approximated by
A* is the effective area of the detector and R is the distance between the detector and the sample. If the temperature is constant over the volume "seen" by the detector, the vapor density is assumed to be uniform over this volume. Performing the volume integration gives
VD is the volume of the sample "seen" by the detector and is the average complexed metal ion density. To improve the signal-to-noise ratio it is convenient to integrate over the energy of the y-ray spectrum. This integration gives p
in which P is the total y-ray count rate, z is the effective detector efficiency, and I , is the probability per unit time for the decay of the radioterbium tracer. I, = (In 2)/Tljz. The energies El and E , are chosen to maximize the Bignal-to-noise ratio and to discriminate against different radioactive species. The fundamental equation for the complexed metal ion density is therefore
In order to obtain absolute complexed metal ion densities, the experimental geometric parameters must be measured, the effective detector efficiency calibrated, and the initial fraction of the radioactive tracer determined. In practice all of these factors are determined simultaneously by loading all sample cells from the same source of radioactive material and calibrating the system. To calibrate the system several sample cells are filled such that all of the metal ions will be in the vapor phase above some critical temperature, T,. These cells are said to be unsaturated with respect to the metal halide. From the known mas5 of the metal halide and the cell volume, the complexed metal ion density is known for a41 temperatures greater than T,. From the measured count rate we have
2460
The Journal of Physical Chemistry, Vol. 83. No. 19, 1979
Peterson et al.
TABLE I: Cell Parameters for Radioactive Exoerimenta cell no.
[TbCl,], mg
[AICI,], mg
cellvol, mL
1 2 GP-1
27.4 3.5 8
2000 1810 1000
88.3 64.9 41.0
puis the known unsaturated complexed metal ion density and P. is the unsaturated count rate. With the geometry of the experimental system unchanged, sample cells with an excess of metal halide (saturated cells) are then utilized to study the temperature and A12C16dimer pressure dependence of the vapor density of the complexed metal ions. The complexed metal ion density is then given by eq 8. Experimental Section Compound Preparation. Terbium chloride was prepared in gram quantities from the corresponding sesquioxide, Tb407 (99.999%). The oxide was dissolved in 6 M HC1,6 mol of NH4CI per mol of TbCI, was added, and the solution was taken to dryness. Anhydrous TbCI, was obtained by slow heating the hydrated salt-NH4C1 mixture under vacuum to 773 K for 8 h.I3 The products were further purified by dynamic vacnum sublimation at 1200 K prior to use. Irradiation of TbCI, for 24 h with a neutron flux of 2 X 10l2cm-2s-' resulted in a fractional conversion of IwTb for ls9Tb of 5 X 10". The 160Tbdecays with a half-life of 72.4 days to an excited state of 'Wy, which then decays instantaneously to the ground state with y-ray emission. Two strong y energies, 0.9 and 1.2 MeV, were used for counting, thus discriminating against decay from radioactive chlorine which was also produced in the irradiation. AICI, samples were prepared by reacting 99.999% AI disks both with HCI gas14 generated in a H2S04-NaCI reactor and high purity HCI (Matheson) which was passed through a cold trap at 193 K prior to contact with the metal reactant. No difference in the quality of product from the two preparative schemes was noted. Experimental Design. In a typical experiment, a cylindrical quartz tube (0.041 L) was loaded with 0.008 g of irradiated TbCI, (0.03 mmol) and 1.0 g of AICI, (3.75 mmol). The vessel was placed in a furnace surrounded, except for a detection slot, by a shield of lead bricks as shown in Figure 1. The end of the tube opposite to that monitored by the detector was kept at a lower temperature by -20 K. The nonvolatilized portion of TbCl,(s) thus remained out of the detection volume. Reported temperatures are those of the cool end of the cell, because vapor equilibrium is established over the condensed phase. A NaI crystal was used to monitor the y activity in the hot end of the sample vessel. The signals were fed through an ampliier/discriminator to a pulse height analyzer. The measured count rate per unit time was proportional to the density of T b atoms in the vapor plus any background rate (noise). Lead attenuates 1-MeV y rays by -80% for a thickness of 2.5 cm. At least 15 cm of lead separated the NaI detection crystal from the cool end of the sample vessel. Background counts from the nonvolatilized portion of the ThCI, were therefore reduced by a factor >lo4. In order to determine the conditions necessary to maintain vapor equilibrium, two types of experiments were performed. The first type of experiment involved measurement of the count rate at a given temperature after equilibrium conditions were established. In order to ensure both thermal and chemical equilibrium, the voltage input to the furnace was set and then the temperature and count rate of the system were monitored as the latter approached equilibrium. The range of measurements varied from
-
P , / T x 10' (atm/K) 3.48 8.58 7.50
T., K 621 521 595
10-'7n, (ionslcm') 7.03 1.22 4.42 THERMOCOUPLES TI
>
Tz
FUlNACE
FURNEE
ANALYSER
COUNTER
Figure 1. Schematic diagram of the experlmtal setup faradioactive
measurements.
temperatures where the observed count rate reached a maximum until temperatures where the background level count rate was reached. In the second type of experiment, the sample temperature was raised beyond the point where the observed count rate reached a maximum, indicating that all of the TbCl,(s) had volatilized. The temperature was then slowly lowered in order to attempt to maintain equilibrium in the vapor phase. It was found that descent rates of 50.13 K/min maintained thermal and chemical equilibrium. Repeated temperature excursions, as described above, for each sample cell resulted in the same maximum count rate and the same background count. While AI& vapors are known to be corrosive at high temperatures? the above fact indicates that no appreciable reaction of A12Ck(g)with the sample vessel occurred below 700 K. Discussion The data for the three cell fillings which were studied in this investigation are given in Table I. Repeated experiments with these samples demonstrated the reproducible and consistent nature of the data. Comparison of the temperature dependence of the vapor density of complexed metal ions for the TbCl8(AlCl3),system with other LnC13(AlC1,), systems is informative. A plot of the natural logarithm of complexed metal ion density, n., vs. the reciprocal of temperature is shown in Figure 2. It has been pointed out recently2 that a steeply rising slope for this type of curve is indicative of a region of liquid-vapor equilibrium. The break in the In n, vs. 103/T(K)curve from the steeply rising curve to the less sloping curve indicates the physical change of the condensed phase from liquid to solid? It is apparent, from comparison of systems in Figure 2, that the cell filling parameters used in this study afforded liquid-vapor equilibrium throughout most of the temperature region. The exact nature of the condensed phase in the vicinity of T,is not well understood, although by comparison with other systems the T, values for these cell fillings are in the region of the liquid to solid condensed phase change. A qualitative comparison of the complex volatilities over liquid chloroaluminate melts across the lanthanide series &e., for Nd3+,Th3+,and Ho3+)shows that they increase
Vapor Density Measurements of Volatile Inorganic Species 1200 I000800 I
TEMPERATURE,K 600 500
"
I
400
The Journal of Physical Chemistry, Vol. 83,No. 19, 1979 2481
333
I
I
160TbClj-AlC13 EXPERIMENT
05-
00-
-0 5
100mm
li~
3
w v)
a
lOmm
t
103
E Temperature Decrease = 0.13 k/mh
'o'l.5
L 1.6
1.7
o 0
2
1.8 119 103/T(K)
2.0
2.:
i1.2
Figure 4. Temperature-dependent count rate data for constant temperature descent experiments. Vapor densities deduced as mentioned for Figure 3 and complex pressures calculated assuming ideal behavior. Imm
10
06
14
22
I8
26
0
IO~/T(K)
Figure 2. Pressure vs. tkmperature plots for characterized lanthaniddactinide chloride-aluminum chloride vapor systems. Vapor pressures of pure terbium chloride and aluminum chloride are included for reference.
160TbC!j-AIC1s EXPERIMENT THERMAL EQUILIBRIUM DATA
g W
'-
1 :
A E
w
B o-Approach from lower temperature
,O ,
A - A o ~ r o o c h from higher temperature
1021.5
1.6
1.7
1.8 1.9 103/T (I()
2.0 2.1
2.2
Figure 3. Temperature-dependent count rate data for equilibrium experiment. Vapor densities were calculated fram initial cell filling factor assuming vapor saturation at 1.2 x i o 5 counts/5 min.
from the lighter to the heavier lanthanides. This observation indicates that results from the radioactive and the optical methods correlate reasonably well. Figures 3 and 4 graphically represent data obtained from the two types of radioactive experiments. The data represented in Figure 3 was obtained after thermal equilibrium was established. If the count rate per unit time at any temperature is P and the background count is S, then F - S is proportional to the vapor density of complexed Tb3+ ions. The measured values of F - S for any experiment are plotted according to values marked on the left abscissa. The uncertainty in the value F - S was
taken to be ( P f S)li2,but it only becomes a significant fraction of the reported value (>2%) below 500 K, which is in the vicinity of the solid to liquid phase change of AlCl,(s). The temperature values used in these plots are from the cooler portion of the vessel, since equilibrium is established there. All cells in this investigation saturated a t an accessible temperature and thus the maximum complexed metal ion density was calculated from the molar amount of TbC13 originally added. The maximum count rate was assigned to the maximum density and lower densities assigned to lower rates proportionally. This discussion also applies to the plot in Figure 4, which is an example of data obtained from experiments where a constant temperature descent rate was employed. Examination of Figures 3 and 4 reveals several interesting features of the TbC13(A1C13),system. It has already been indicated that the steeply sloping nature of the data (due to a highly endothermic process) shows that vapor densities of complexed Tb3+ ions were measured over a condensed liquid phase for most of the temperature region. Both Figures 3 and 4 show anomalous behavior in the vicinity of 475 K which is close to the temperature of the solid-liquid phase change of AlC&. This suggests a change in activity of TbC13, which would be expected as the interaction of TbC13 with the environment changes. It appears that a8 the TbC13-A1C13liquid mixture solidifies the vapor pressure of Tb3+containing species is enhanced. The slopes of both curves (Figures 3 and 4) are nearly identical in every region indicating that chemical equilibrium is maintained at a descent rate of 0.13 K/min. This was not true for experiments run with a descent rate of 0.18 K/min. Points for the plot in Figure 3 were obtained by approaching the desired temperature from both higher and lower temperature indicating that matrix effects were not a problem throughout the temperature region if sufficient time for equilibrium was allowed. Conclusions The use of radioactive tracers to follow the vapor density of that complexed metal ion as a function of temperature and the vapor pressure of a complexing agent h a s been shown to be a viable technique. Inspection of any compilation of nuclides will reveal that the technique could have wide application. Studies of lanthanides, actinides,
No. 19, 1979
Peterson at al.
TABLE I1 : Radioactive Properties of Candidate Isotopes
path length, assuming a molar absorptivity of 25 L/mol. cm. Examination of Figures 3 and 4 shows that the radioactive method in this case detected complexed metal ion densities of 6 X lo1*complexed ions/cm3 and lower depending on the care taken to minimize the background count rate.16 This increase of two orders of magnitude in sensitivity makes it possible to probe lower temperature and pressure regions not accessible to the spectrophotometric technique. In addition, the radioactive technique does not have an upper limit of the vapor density of complexed metal ions which can be measured and thus any magnitude of complexed metal ion density changes can be determined from one experiment. Only a IO2complexed ions/cm3 change in vapor density can be measured spectrophotometrically (assuming a 10-cm optical cell and an E of 25 L/mol cm). The precision of the data obtained from the radioactive experiment is also superior to that which can be obtained from the spectrophotometric method. The precision of the complexed metal ion density derived from optical data is limited by the absorbance measurement made by the spectrophotometer. A reasonable lower limit estimate of this uncertainty for a recording spectrophotometer is 3%. The precision of the complexed metal ion density from the counting experiment is dependent upon the experimental design, which can be optimized. Depending upon the geometry of the experiment and the counting period we determined the precision of vapor density to be 51% The increase of precision of the vapor density from radioactive experiments can be an important factor when temperatureand pressure-dependent complexed metal ion density changes are used to derive apparent formation thermodynamics for vapor complexes. This type of thermodynamic characterization of a vapor system is currently underway in our laboratory for TbCl3(AlCl3),, using data obtained in a manner described here.
2462
SOtope
The Journal of Physical Chernistw, Vol. 83,
atomica mass, A
lifetime
50.9448 27.8 days 53.9404 291 days 59Ft 589309 45days "CO 59,9338 5.27 years 65Zn 64.9292 245 days 91Y 90.9069 57.5 days "Zr 94.9079 6 5 d a y s Io3Ru 102.9063 40 days " ' C e 140.9080 32.5 days '"Nd 146.9158 11.1days ' 5 4 E ~153.9228 16 years '"Tb 159 9268 73 days lS1Hf 180.9491. 44.6 days 237U 237.0486 6.75 dags 239Np 239.0529 2.35 days 237Pu 237.0483 45.3 days 240Am 50.8 h 243Cm243.0614 28.5 years "'Bk 250.0785 3.222 h 249Cf 249.0747 351 years "'Es 251.0799 33 h "Cr
54Mn
E,, M e V 0.324 0.835 1.102 1.332 1.114 1.21 0.723 0.497 0.144 0.53 0.72-1.28 0.875-1.18 0.482 0.208 0.278 O.10lc 1.000 0.278 1.032 0.388 0.115c
specific activityb
2.047 X 10" 1.847 X 10'" 1.093 X 10" 2.515 X l o 9 1.822 X 10" 5.546 x 1 O ' O 4.699 x 10" 7.043 X 10" 6.330 X 10'' 1.778 X lo'* 3.225 X 10' 2.483 X 1 0 L o 3.592 X 10" 1.812 X 10" 5.169 X 10" 2.700 X 10" 5.71 x lo1' 1.146 X l o 8 8.635 X 10" 9.08 X l o 6 8.40 X 10"
a From r e f 17. T h e specific activities are given in u n i t s of disintegrations p e r minute m i c r o g r a m . SA = 4.17449 X 101'/(Tl,2A). K X rays.
and transition metals are examples. Table I1 lists pertinent information for a representative sample of elements whose vapor chemistry could be studied by using this radioactive technique. The determination of vapor densities of complexed metal ions by this technique can be utilized in the investigation of systems which cannot be measured by the spectrophotometric method. For example, in the TbCl,(AIU,), system the spectrophotometric experiments are of only marginal utility due to the weak nature of the Tb3' absorption bands. Not only is the radioactive method a more versatile technique, but it is a more convenient method for taking the quantity of data necessary for precise thermodynamic and chemical characterization. Perhaps the greatest strength of the technique is that it is a direct measure of the complexed metal ion density and is not dependent upon the chemistry of the system. Accurate measurements of multispecies vapor systems can be readily accomplished, because the measured count rate is related to the vapor density only through the accurately determined specific activity of the radioactive isotope being used. Of course the geometry is an extremely important consideration in this method, but a well-characterized counting geometry is not difficult to maintain. The direct relationship of the measured count rate and vapor density in the radioactive experiment does not apply to the measured absorbance and vapor density of the spectrophotometric experiment. The assumptions necessary to derive vapor density information f,om optical absorption data were mentioned previously and were recently critically reviewed.12 In light of these comments, the direct relationship which exists with radioactive experiments is a significant advantage when studying temperature- and pressure-deperident effects in complex vapor systems. Two other important advantages of the radioactive experiments for vapor density measurements are the sensitivity and precision of the technique. A carefully executed optical experiment will detect approximately 5 x complexed ions/cm3 in a sample vessel with a 10-cm
a
References and Notes (I) J. W. Hastie, "High Temperature Vapors", Academic Press, New York, 1975. (2) F. P. Emmenegger, Inorg. Chem., 16, 343 (1977). (3) W. F. Krupke, Lawrence Livermore Laboratory Report UCID-16620, 1974. (4) J. P. Hessler, F. Wagner, Jr., C.W. Williarns, and W. T. Carnail, J . Appl. Phys., 48, 3260 (1977). (5) R. R. Jacobs, W. F. Krupke, J. P. Hessler, and W. T. Carnall, Opt. Comrnun., 21, 395 (1977). (6) W. T. Carnall. J. P. Hessler, H. R. Hoekstra, and C. W. Williams, J . Chern. Phys., 68,4304 (1978). (7) W. T. Carnall, J. P. Hessler, C. W. Williams, and H. R. Hoekstra, J. Mol. Structure, 46, 269 (1970) (8) G.E. Vrieland and D. R. Stull, J. Chem. Eng. Data, 12,532 (1967). (9) H. A. Oye and D. M. Gruen, J . A m . Chcrn. Soc., 91, 2229 (1969). (10) E. J. Peterson, J. P. Hessler, and J. A. Caird, to be submltted for publication.
(11) H. A. Oye and D. M. Gruen, "Metal Halide-Group 111 Halide Gas Complexes with Emphasis on Aluminum Chloride", 10th Materials Research Symposium, Gaithersburg, Md., Sept 1978,in press. (12) J. P. Hessler, J . Phys. Chem., in press. (13) M. P. Taylor and C. P. Carter, J . Inorg. Nucl. Chem., 24, 387 (1962). (14) G.Brauer, "Handbook of Preparative Inorganic Chemistry", Vol. I, 2nd ed, Academic Press, New York, 1963. (15) E. J. Peterson et al., lo be submitted for publication. (16) The fact that 6 X 1014complexed metal ions/cm3 were detected in these ex eriments was dependent on the conversion factor = 5 X lo-'. By doubling or tripling the irradiation N("?b)/N('?b) time, greater sensitivity due to increases in the specific activity would be realized. In actinide systems, for example 243Cm,no "activity dilution factor" would exist. (17)C. M. Lederer and V. S. Shirley, "Table of Isotopes", 7th ed,Wiley, New York, 1978.
