J. Phys. Chem. 1994,98, 1482-1486
1482
Thermodynamic Functions of Element 105 in Neutral and Ionized States V. Pershina' and B. Fricke Theoretical Physics Department, University of Kassel, 3500 Kassel, Germany
G. V. Ionova Institute of Physical Chemistry, Russian Academy of Sciences, Moscow Leninski pr. 31, I I791 5 Moscow, Russia
E. Johnson Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6375 Received: September 16, 1993"
T h e basic thermodynamic functions, the entropy, free energy, and enthalpy, for element 105 (hahnium) in electronic configurations d3s2, d%p, and d4sl and for its +5 ionized state (5f14) have been calculated as a function of temperature. The data a r e based on the results of the calculations of the corresponding electronic states of element 105 using the multiconfiguration Dirac-Fock method.
I. Introduction During recent years there has been a considerably growing interest in the physics and chemistry of the transactinide elements. Elements 104 and 105 and their halides have been studied both experimentallyI4 and theoreti~ally.5-~An extensively used method for experimental investigations of the properties of these elements is thermal gas chromatography. With this technique, data on thevolatility of element 104in comparison with its analogs, Zr and Hf, have been obtained3 and the volatility of element 103 as a possible analog of TI has been investigated.8 The gas chromatography has been applied as well to the investigationI4 of the volatility of chlorides and bromides of elements 104 and 105 along with their analogs, ZrIHf and NbITa, respectively. An important aspect of the study was the investigation of the physicochemical properties of the heavy elements as a function of electronic configuration. A number of experiment^^,^ were carried out to study the volatility of the elements depending on their electronic configurations, and theoretical estimations of the sublimation enthalpy of element 104 as a function of electronic configuration have been done in ref 10 using some correlations. Estimations of the sublimation enthalpy for transactinide elements are of importance for the gas chromatography experiments. Besides, the more complete study of the physics and chemistry of the transactinide elements should include the knowledge of their thermodynamic functions, especially as a function of temperature. From the thermodynamic data it is possible to predict the chemical behavior. The calculation of thermodynamic data, when no experimental data exist, is possible using spectroscopic levels of the gaseous atoms. Provided the latter are not known from experiment, they can be calculated using relativistic atomic codes. Thus, in this work we present the basic thermodynamic functions, S , G, and H,for element 105, in different electronic configurations as a function of temperature, which were calculated using the energy levels obtained from the multiconfiguration Dirac-Fock (MCDF) calculations. These calculations were performed for the groundstate electronic configuration of element 105 d 3 ~ 2 ( ~ Fas) , well as for the excited-state electronic configurations, dSsp(6G) and d4s(6D). The sublimation enthalpy of the metallic hahnium has been estimated using the MCDF atomic data. 0
Abstract published in Advance ACS Absrracrs. January 1, 1994.
0022-365419412098- 1482%04.50/0
TABLE 1: Calculated Relative Energy Eigenvalues for the Lowest Energy State That Is Dominated by the dW('F) Configuration as a Function of Total Angular Momentum J for V, Nb, Ta, and Ha angular energy momentum exptll' energy" element and parity (eV) (cm-l) (cm-I) V
3/2+ 5/2+
7/2+ 9i2+
Nb
3i2+ 5/2+ 7/2+
Ta
9/2+ '/2+
5/2+ 7/2+ Ha
0.0 0.0161 0.0386 0.0665
0.0 0.0525 0.1204 0.1965
0.0
9/2+
0.2034 0.4255 0.6399
'/2+
0.0
5/2+
0.4571 0.8264 1.0966
7/2+
9i2+
0.0 129.85 3 11.3 1 536.32
0.0 423.41 971.03 1584.77
0.0 1640.42 3431.66 5160.79 0.0 3686.71 6665.28 8844.56
0.0 137.38 323.42 553.02 0.0 444.1 1 101 1.32 1662.57
0.0 2010.10 3963.92 5621.04
0.0 (4746.25) (8149.68) (1001 1.08)
For Ha the data are normalized and extrapolatedto the experimental values for V, Nb, and Ta. Results of the present MCDF computations and the thermodynamic data calculated from them are presented in the next sections. 11. Results of the MCDF Calculations The MCDF c a l c ~ l a t i o n shave ~ ~ shown the ground-state electronic configuration of H a to be dV(4F). The present calculations show that the next excited states are d 3 ~ p ( ~ Gand ) d%1(6D), lying at 1.9(f0.4) and 2.0(f0.4) eV higher in energy, respectively. The energies of the lowest energy states that are dominated by the dW(4F), d3sp(6G), and d4s1(6D)configurations as a function of the total angular momentum quantum number J for hahnium along with its group-5 analogs are presented in Tables 1-3. Since the MCDF method does not give the excitation energies as accurately as desired (mainly due to the influence of the core polarization, which cannot be taken into account by the program), the accuracy of the results has been increased by using an extrapolation procedure to obtain "experimental" energies. The extrapolation procedure used is based on ideas from the finite difference method in numerical analysis12 and is described in 0 1994 American Chemical Society
The Journal of Physical Chemistry, Vol. 98, No. 5, 1994 1483
Thermodynamic Functions of Element 105
TABLE 2 Calculated Relative Energy Eigenvalues for the Lowest Energy States That Is Dominated by the d49(6D) Configuration as a Function of Total Angular Momentum J for V, Nb, Ta, and Ha element V
angu Ia r momentum and Daritv 1/2+
'/2+ 5/2+
l/2+ 9/2+
Nb
1/2+
'/2+ 5/2+ 7/2+ 9/2+
Ta
1/2+
3/2+ 5/2+ 7/2+ 9/2+
Ha
'/2+
3/2+ 5/2+ 7/2+ 9/2+
energy (eV)
(cm-l)
exptlll energy" (cm-1)
0.0 0.0053 0.0140 0.0253 0.0369 0.0 0.0163 0.0423 0.0763 0.1148 0.0 0.031 1 0.1361 0.2301 0.3585 0.0 0.1480 0.3530 0.5510 0.7330
0.0 42.67 112.92 204.23 297.86 0.0 131.47 341.17 615.39 925.91 0.0 250.84 1097.7 1 1855.86 2891.46
0.0 40.88 107.81 199.24 312.57 0.0 154.19 391.99 695.25 1050.26 0.0 216.84 1484.66 2475.79 3592.48
0.0 1193.68 2847.10 4444.06 5911.97
0.0 (1022.64) (3851.03) (6060.04) (7656.90)
a The data for Ha are extrapolated and normalized to the experimental data for V, Nb, and Ta.
TABLE 3: Calculated Relative Energy Eigenvalues for the Lowest Energy State That Is Dominated by the djSp(6C) Configuration as a Function of Total Angular Momentum J for V, Nb, Ta, and Ha element V
angular momentum and parity 3/~-
5/r l/29 / ~ 111213/2-
Nb
'12SIT712-
9/2-
1112-
Ta
13/23/2512l/29 / ~ -
"/21312-
Ha
3/~-
'129/211/2-
l'l2-
energy (eV)
(cm-I)
0.0 0.0102 0.0245 0.0429 0.0654 0.0920 0.0 0.0353 0.0837 0.1448 0.2176 0.3015 0.0 0.1450 0.3396 0.5705 0.8378 1.1521 0.0 0.3730 0.7360 0.9440 1.4440 2.6540
0.0 82.26 197.93 345.99 527.45 741.98 0.0 284.69 675.04 1167.81 1754.94 2431.59 0.0 1169.43 2738.87 4601.08 6756.86 9291.69 0.0 3008.25 5935.84 7613.36 11645.86 21404.50
exptlll energy" (cm-1) 0.0 88.40 211.09 367.30 555.70 774.99 0.0
309.01 631.96 1265.26 1763.14 2204.46 0.0 1793.80 3175.61 5297.06 7624.18 0.0 (4814.81) (7386.7 3) (9429.60) (14250.86)
For Ha the data are normalized and extrapolated to the experimental values for V, Nb, and Ta. (1
application to elements 104 and 105 in refs 5a,b. The uncertainty in the ionization potentials presented there is less than 0 . 3 eV. These experimental values, shown in Tables 1-3 in the parentheses, can be used for calculations of the thermodynamic functions and predictions of chemical properties. A general trend in the group is an increase in energies (more negative) of the excited states in going from V to Ha. The first fine-structure level ( J = 5 / 2 ) for H a (d3s2) has an energy which is nearly enough to bring Ta to the next excited state (4P). Thus, much higher temperatures are needed to make the excited states of H a occupied in comparison with the analogs.
111. Thermodynamic Functions and Sources of Data
A model of a monatomic ideal gas was used to calculate the entropy, enthalpy, and free energy of hahnium. The expression for the translational entropy of an ideal gas is
S = N0k[ In( Z ( 2 m nh3P kT)'/'kT)
+-:]
(1)
Here NO= 6.022 X mol-', k = 1.380 X 10-23 J X K-1, P = 1 atm = 1.013 25 X 106 dyne cm-1; m is the mass of Ha equal to 266/N0, and h = 6.626 X J s. The calculation of this function, as well as of the free energy, for an ideal gas requires a calculation of the specific form of the partition function Z , i.e.
Here gk is a statistical weight for electron states (or degree of degeneracy of a level) equal to 2 5 1, and ACJis the difference between energies of the fine-structure components for a given term of the element. The summation is taken over all possible values of the total angular momentum J for all L and S states. Considering the monatomic gas in a temperature interval between 273 and 4000 K, we make here the following comment. As the gas temperatures increase, the number of atoms in excited states also increases with some of them even being ionized. When the temperatures are not too high ( T > Zion.13 Thus, a nonionized gas can be considered at temperatures T > ACJ
189 206 224 259 293 346 519 695 1038 1390 1731 2085 2423 2780 T>>ACJ
4.000 4.000 4.000 4.000 4.000 4.000 4.003 4.006 4.065 4.200 4.460 4.856 5.288 5.788 28
1.386 1.386 1.386 1.386 1.386 1.386 1.387 1.387 1.402 1.435 1.495 1.580 1.666 1.756 3.332
188.05 189.90 191.56 194.54 197.17 200.63 209.08 215.05 223.61 229.86 234.99 239.49 243.40 246.93 >286.78
TABLE 5: Calculated Electron Partition Function 2 and the Entro y S for Element 105 in Electronic Configuration d3sp&) T
(K)
(cm-I)
Z
In Z
S (J mol-' K-I)
273 298 323 373 423 500 750 1000 1500 2000 2500 3000 3500 4000 T >> ACJ
189 206 224 259 293 346 519 695 1038 1390 1731 2085 2423 2780 T>> ACJ
4.000 4.000 4.000 4.000 4.000 4.000 4.003 4.006 4.065 4.239 4.530 4.949 5.441 6.039 30
1.386 1.386 1.386 1.386 1.386 1.386 1.387 1.387 1.402 1.444 1.511 1.599 1.694 1.798 3.401
188.05 189.90 191.56 194.54 197.17 200.63 209.08 215.05 223.61 229.91 235.14 239.66 243.65 247.30 >28 1.74
TABLE 6 Calculated Electron Partition Function 2 and the Entropy S for Element 105 in Electronic Configuration d4s1PD) T ~
273 298 323 373 423 500 750 1000 1500 2000 2500 3000 3500 4000 T >> ACJ
189 206 224 259 293 346 519 695 1038 1390 1731 2085 2423 2780 T>>ACJ
2.016 2.028 2.041 2.077 2.122 2.207 2.557 2.943 3.677 4.388 5.230 6.088 6.933 7.805 54
0.701 0.707 0.714 0.731 0.752 0.792 0.939 1.079 1.302 1.479 1.655 1.806 1.936 2.055 3.959
182.36 184.23 185.98 189.09 191.90 195.69 205.36 212.42 222.77 230.22 236.32 241.37 245.66 249.42 >310.82
The values obtained for Z and corresponding values of the entropy for P = 1 atm are presented in Tables 5 and 6. For the heavy-metal vapors, sometimes in practice a range of high temperatures is of importance, so that the temperature is large in comparison with the fine-structure intervals, T >> ACJ. In this case, onecan put e-A*JJT 1 in expression 2, and Z becomes simply the total number of the fine-structure components ( 2 s + 1)(2L + 1). In thiscase thevalueofspecific heat becomesconstant (C, = 3/2) (see ref 12). Thus, at T >> AQ, the values of 2 for Ha in electronic configurations dW, d%p, and d4s are 28,30, and
TABLE 7: Calculated Values of the Free Energy, C, and the Enthalpy, H,for Element 105 in Electronic Configuration d Y ( 'F) T (K) TS (kJ mol-') 4 (kJ mol-') H (kJ mol-') 273 298 323 373 423 500 750 1000 1500 2000 2500 3000 3500 4000
51.338 56.582 61.873 72.564 83.402 100.315 156.810 215.053 33 5.408 459.713 587.475 718.464 85 1.913 987.725
45.664 50.388 55.159 64.8 11 74.610 89.922 141.220 194.267 304.229 418.140 535.510 656.106 779.161 904.581
5.673 6.194 6.714 7.753 8.792 10.393 15.590 20.786 31.179 41.572 51.965 62.358 72.751 83.144
TABLE 8 Calculated Values of the Free Energy, C, and the Enthalpy, H, for Element 105 in Electronic Configuration d3SP(W T (K) TS (kJ mol-I) -G (kJ mol-') H (kJ mol-I) 273 298 323 373 423 500 750 1000 1500 2000 2500 3000 3500 4000
51.338 56.582 61.873 72.564 83.402 100.3 15 156.810 215.053 335.408 459.820 587.850 718.980 852.775 989.200
45.664 50.388 55.159 64.8 11 74.610 89.922 141.220 194.267 304.229 418.320 535.8 85 656.6 34 780.052 906.048
5.673 6.194 6.7 14 7.753 8.792 10.393 15.590 20.786 31.179 41.500 51.965 62.346 72.723 83.152
TABLE 9 Calculated Values of the Free Energy, C, and the Enthalpy, H, for Element 105 in Electronic Configuration d4s1(6D) T (K) TS (kJ mol-') -G (kJ mol-') H (kJ mol-I) 273 298 323 373 423 500 7 50 1000 1500 2000 2500 3000 3500 4000
49.781 54.898 60.071 70.529 81.542 97.843 154.020 212.488 334.15 1 460.441 590.8 02 724.112 859.808 997.666
44.107 48.706 53.357 62.776 72.749 87.449 138.430 191.703 302.972 418.868 538.836 661.754 787.056 9 14.52 1
5.673 6.194 6.714 7.753 8.792 10.393 15.590 20.786 31.179 41.572 5 1.965 62.358 72.751 83.144
54, respectively. The corresponding values of the entropy are presented in Tables 4-6. The free energy for element 105 has been calculated using the formula
G=-N,kT
[In( Z ( l a m k T ) ' / * k T ) ] h3P
(6)
The calculated G's for H a ( d V ) , Ha(d3sp), and Ha(d4s1)as a function of temperature are given in Tables 7-9. The enthalpy, H,can be calculated from the general expression
G=H-TS (7) The values obtained for H for the Ha states under discussion are also presented in Tables 7-9. A Ha5+ ionized state was also included in the present consideration. For the 5P4 electronic configuration the value of
The Journal of Physical Chemistry, Vol. 98, No. 5, 1994 1485
Thermodynamic Functions of Element 105
TABLE 1 0 Calculated Values of the Entro S, the Free Enerw, C. and the EnthalDv. H.for H a V 5 )
,pr:
(K)
T (cm-I)
273 298 323 373 423 500 750 1000 1500 2000 2500 3000 3500 4000
189 206 224 259 293 346 519 695 1038 1390 1731 2085 2423 2780
a
5 -
10
-
H
S TS (J mol-' K-') (kJ mol-')
-G (kJ mol-')
(kJ mol-')
48.191 53.182 58.153 62.266 78.529 94.562 148.162 203.535 317.942 435.889 556.451 679.113 803.445 929.316
42.517 46.982 51.439 60.513 69.736 84.169 132.586 182.748 286.759 394.275 504.485 616.725 730.689 846.172
5.673 6.205 6.7 14 5.523 8.793 10.393 15.576 20.781 31.179 41.618 51.965 62.387 72.751 83.144
176.53 178.38 180.04 183.02 185.65 189.13 197.55 203.53 211.96 217.94 222.58 226.37 229.56 232.33
12
p .P
Eb = AN
8-
' -.-
+
B
A
.
6-
E
P
4t
For Ha5+(5fI4),2 = 1.
TABLE 11: Approximate Solid-state Electronic Configurations of the Transition Metals of GrouDs 4-7 group 4 group 5 group 6 group 7 Ti V Cr Mn dsXspX d4s d5s d6s + d5sp Zr Nb Mo Tc d3-xspX d4s d5s dGXspX Hf Ta W Re d%pX dkxsp' d5s d%pX ~~
104
105
106
107
dkXspX
d5s
dGXspX
2 is equal to unity. The calculated thermodynamic values for Ha5+ are presented in Table 10. The values of the partition function can also be used for calculating some other physicochemical characteristics such as, for example, chemical potentials. The latter can be used for calculations of a partial pressure of the gaseous element. IV. Sublimation Enthalpies of the Metals A. Electronic Structure of the Transition Metals. It was shownI4 that the highly directional properties of the d-electrons determine the crystal structure for transition metals. The following correlation has been accepted for the transition metals (see Table 11): 1. For metals which are likely to have electronic configuration dx (0 < x < 2), the crystal lattice has the fcc structure. 2. For metals with d5 configuration (at or near it), the crystal structure is bcc. 3. For metals with intermediate configurations dx (2 < x < 4), the crystal lattice is hcp. V, Nb, Ta, and H a belong to the third class. It means that the lattice may change the symmetry from bcc to hcp depending on the temperature. Our molecular orbital calculations7 of hahnium compounds show that there is some electron population of the 7 ~ 1 orbitals ,~ of Ha. Analogously, we can assume that in the metallic hahnium as well as in metallic elements 106-111 the np electrons are available. Metals of group 4 have d3-xsp' configuration with x approximately equal for Ti and Zr and much larger for Hf. The presence of the p-electrons in the electronic configuration of Hf stabilizes the hcp structure. Hf transforms to the high-temperature bcc state at a very high temperature. Apparently, element 104 will be preferentially in the hcp structure too. But if consideration is taken of the fact that in the ground state the 7p orbitals of element 104 have a large electron population,15J6the hcp fcc transformation is to be expected at higher temperatures.
-
-2
,
, 20
V
,
10
Ha
Ta
Nb ,
,
I
60
,
I
,
80
I
100
,
I
120
Atomic number, N Figure 1. Sublimation energy of a metal Li&,bl, cohesiveenergy E,, and
the difference between energies of electronic configurations in the gas phase and in the solid state M(d4s43s2)(filled triangles) and M ( d 3 s p d3s2)(open triangle for Ha) as a function of the atomic number. A filled square is A&bl of Ha for the electronic configuration d4s in the metal, and an open square is A&bl for the d3sp electronic configuration. In group 5, T a and Ha can be considered a borderline case on the bcc side of the border. In group 6 the p-valence electrons are high in energy owing to a strong orbital effect in the half-occ~piedd~ shell. This requires a bcc structure. For metallic Tc and Re a larger population of the p-atomic orbitals was accepted14 in comparison with N b and Ta, and the d%p"configuration was considered as an equivalent to the d4+*sp" one. This would stabilize the hcp structure in all three metals of the group (Tc, Re, and element 107), with the effect being more pronounced in the case of element 107 due to strong relativistic effects. B. SublimationEnthalpy of the Metallic Hahnium. Assuming that hahnium has the same structure in the metallic state as N b or Ta having the bcc lattice, we will try to estimate its sublimation enthalpy using the results of the present MCDF calculations. The sublimation enthalpy can be expressed17 as where Eb is the valence state bonding energy of the metal (or the cohesive energy which can be measured as the enthalpy of sublimation to a gaseous atom with the same electronic configuration as in the metal) and AE is the difference between the energy of the ground-state electronic configuration realized in the gas phase and the energy of the exited-state configuration realized in the condensed state. Thus we can estimate U s u b l knowing the values of A,??(d4sa3s2)or A,??(d3sp-d3s2),and E b . For the lanthanides and actinides it was ~ h o w n * that ~ J ~the bonding energy Eb is a smooth function of the atomic number N. E b for the group 5 elements V, Nb, and T a can be determined using eq 8. There, AE = E(d4s) - E(d3s2)for V, Nb, and Ta are experimental spectroscopic data," and A E = E(d4s) - E(d3s2) = 2.0(f0.4) eV for H a was obtained as a result of the present atomic MCDFcalculations. Thus knowing AEvalues for all theelements under consideration and AHsubl19 for V, Nb, and Ta, we have found their E b values. In accordance with the idea developed in ref 18 we see that E b is a linear function of N for the group 5 elements (Figure 1). Thus we can find E b for Ha, which together with the value of A,??(d4s+13s2) gives Afzsubl = 10.1 eV or 973.54 kJ/mol. Using AE(d3sp-d3sz)equal to 1.9(*0.4) V gives f i f i s u b l
1486 The Journal of Physical Chemistry, Vol. 98, No. 5, 1994
= 10.2 eV. These estimated values nevertheless seem to be enhanced. Calculations of the sublimation enthalpy at the mixed d%pX configuration is needed to give the final value of AHsubl for Ha.
Acknowledgment. V.P.would like to thank the W. E. Heraeus Stiftung for financial support. This research was cosponsored by the Division of Chemical Sciences, Office of Basic Energy Sciences, US.Department of Energy, under Contract DE-FCO585ER25000 with Martin Marietta Energy Systems, Inc. References and Notes (1) Gtiggeler, H. W.; J0st.D. T.;Baltensperger, U.; Ya,N.-Q.;Gregorich, K. E.; Gannett, C. M.; Hall, H. L.; Henderson, R. A,; Lee, D. M.; Li, J. D.; Nurmia, M. J.; Hoffman, D. C.;Tiirler, A,;Lienert, Ch.;SchHdel,M.; Briichle, W.; Kratz, J. V.; Zimmermann, H. P.; Scherer, U. W. Report PSI, PSIBericht No. 49, 1989. Radiochim. Acta, in press. (2) Zvara, I.; Belov, V. 2.; Chelnokov, L. B.; Domanov, V. P.; Hussonnois, M.; Korotkin, Yu. S.; Schegolev, V. A.;Shalayevskii, M.R. Inorg. Nucl. Chem. Lett. 1971, 7, 1109. (3) Zhuikov, B. L.; Chuburkov, Yu. T.; Timokhin, S. N.; Zvara, I. Radiochim. Acta 1989, 46, 113. (4) Hoffman, D. C. Chemistry of the Transactinide Elements. In Proceedings of the Robert A . Welch Foundation Conference on Chemical Research. XXXIV: Fify Years with Transuranium Elements; Houston, T X , 1990; Vol. VIII, p 255. ( 5 ) (a) Johnson, E.; Fricke, B.; Keller, D. L., Jr.; Nestor, C. W., Jr.; Tucker, T. C. J. Chem. Phys. 1990, 93, 8041. (b) Fricke, B.; Johnson, E.
Pershina et al. Radiochim. Acta, to be published. ( 6 ) Glebov,V.A.;Kasztura,L.;Nefedov,V.S.;Zhuikov,B. L. Radiwhim. Acta 1989, 46, 117. (7) (a) Pershina, V.; Sepp, W.-D.; Fricke, B.; Rosen, A.J . Chem. Phys. 1992,96,8367. (b) Pershina, V.; Sepp, W.-D.; Fricke, B.; Kolb, D.; Schidel, M.; Ionova, G. V. J. Chem. Phys. 1992, 97, 1116. (c) Pershina, V.; Sepp, W.-D.; Bastug, T.; Fricke, B.; Ionova, G. V. J . Chem. Phys. 1992,97,1123. ( 8 ) Jost, D. T.; GHggeler, H. W.; Vogel, Ch.; Schtidel, M.; Jgger, E.; Eichler, B.; Gregorich, K. E.; Hoffman, D. C. Inorg. Chim. Acra 1988, 146, 255. (9) (a) Zhuikov, B. L.; Chuburkov, Yu. T.; Timokhin, S.N.; Zvara, I. Radiochim. Acra 1989, 46, 113. (10) Eichler, B.; Hiibener, S.;GHggeler, H. W.; Jost, D. T. Inorg. Chim. Acta 1988, 146, 261. (1 1) Moore, C. E. Atomic Energy Leuels;Circular of the National Bureau of Standards 476; National Bureau of Standards: Washington, D.C., 1949; Vols. 1-111. (12) Booth, A.NumericalMethods, 3rd ed.; Butterworth: London, 1966; P 7. (13) Landau, L. D.; Lifshitz, E. M.Sratistical Physics, Part 1; Permagon Press: Oxford, U.K., 1980; p 132. (14) Pecora, L.; Ficalora, P. J. Solid State Chem. 1979, 27, 239. (15) Glebov,V.A.;Kasztura,L.;Nefedov,V.S.;Zhuikov,B.L.Radiochim. Acta 1989. 46. 117. (16) Johnson, E.; Fricke, B.; Keller, 0. L., Jr.; Nestor, C. E.; Tucker, T. C. J. Chem. Phys. 1990, 93,8041. (17) Brewer, L. J. Opt. SOC.Am. 1971, 61, 1101. (18) Johanssen, B.; Rosengreen, A. Phys. Reu. B 1975, 1 1 , 1367. (19) (a) Clark, R. J. H. In Comprehensive Inorganic Chemistry, Bailar, J. C., Ed.; Pergamon Press: Oxford, U.K., 1973; Vol. 3, p 494. (b) Brown, D. In Comprehensive Inorganic Chemistry; Bailar, J. C., Ed.; Pergamon Press: Oxford, U.K., 1973; Vol. 3, p 559.
