W. L. MEDLIS
1172
The accumulation of the missing data will be useful to the growing field of high temperature chemistry. Acknowledgment.-The assistance of Messrs. R. W. Bane, B. D. Holt, J. A. Goleb and R. V.
Vol. 65
Schablaske in performing special analyses is greatly appreciated. We also wish to thank F. J. Karasek for fabricating the zirconium rod and foil for these experiments.
THERMOLUMINESCENCE I N ARAGONITE AND MAGNESITE BY W. L. MEDLIN Socony Mobil Oil Company, Inc., Field Research Laboratory, Dallas, Texas Received December 8%.1960
The important features of thermoluminescence in aragonite and magnesite have been studied by investigating the properties of synthetic samples. The synthetic aragonite samples were prepared by precipitation a t 80-90" and the magnesite samples were precipitated by hydrothermal techniques. The results of adding all of the impurities which may occur in natural samples and which are likely to produce thermoluminescence have been investigated by coprecipitating each of them in synthetic samples. The effects of vacancy defects have also been considered. The results show that all of the thermoluminescence in natural samples is due to the presence of divalent magnanese. It was also found that Co++ and N i + + quench the h4n++ luminescence in both minerals whereas F e + + is a quencher in aragonite only. Quantitative results have been compiled for the luminescent efficiency of each of the M n + + glow peaks in aragonite and magnesite as a function of impurity concentraton. Quantitative results have also been included to illustrate the relative quenching effects of Fe ++, Co++ and I%'-+. The impurity concentrations in the synthetic samples were determined by colorimetric methods. Measurements of isothermal decay curves were made for each of the prominent glow peaks in aragonite and magnesite and the effect of varying the temperature and the excitation time was investigated. The activation energies associated with the traps for most of the glow peaks also were determined. Glow curves for natural samples are compared with the curves for synthetic samples and the results interpreted on the basis of impurity concentrations in the natural samples. Practical applications of the results are discussed.
which provided an exposure of about 500 roentgens. I. Introduction The results of this investigation satisfactorily All of the common naturally occurring carbonate minerals including calcite, dolomite, aragonite and explain all of the important thermoluminescent magnesite are thermoluminescent to some extent. properties of natural samples of aragonite and The properties of calcite and dolomite have been magnesite . investigated'J and it has been shown that the 11. Experimental Procedure and Results prominent glow peaks found in natural samples are The precipitation of aragonite by the mixing of due to the presence of divalent manganese. This calciumdirect and carbonate ions in solution is hindered by the paper describes an investigation of the thermolumi- formation of calcite which is the most stable polymorph of nescent properties of aragonite and magnesite CaC03 under normal conditions (a third form, vaterite is which are closely related in crystal structure to less stable than aragonite). However, a t elevated temperatures the relative stability of aragonite increases and between calcite and dolomite. 80 and 100" it is possible to obtain nearly pure aragonite The general procedure followed here is the same by initially seeding the solution. one used for the calcite and dolomite investigations. A more convenient method which takes advantage of the High purity samples containing one or more added differences in crystal structure between aragonite and calwas used here. It was found that the presence of trace impurities were prepared by coprecipitation meth- cite amounts of such impurities as Sr or H g + + in the original ods and the thermoluminescent properties of the solution favors the precipitation of aragonite because of synthetic samples were compared with the char- similarities in coordination numbers and ionic radii. The acteristics of natural samples. The effects of theoretical coordination number of the Ca++ ion in calcite is only 6 whereas it is 8 in aragonite; furthermore, the ionic certain lattice defects such as ion vacancies were radius of C a + + is slightly larger in aragonite. I t follows also studied. that impurity ions such as H g + + and Sr++ which exhibit In determining the concentrations of the various an 8 coordination only and have about the right ionic radii impurities in the synthetic samples, the colorimetric should enhance the precipitation of aragonite. In practire, was found to be better for this purpose than H g + + and methods used for the calcite and dolomite investi- Sr++ optimum concentration was about 1000 p.p.m. gations were applicable with only minor changes in theImproved results were obtained by controlling both the procedure. Analyses of natural samples were made concentrations of the C a + + and C03' solutions and the rate spectrographically. The glow curve apparatus of addition of the Ca++ solution. It was found that 0.05 M solutions of Ca(NO& and Xa2CO3solutions provided used here has been described in a previous article.3 the best results when the C a + + solution was added a t a rate The samples were heated a t a constant rate of of 20 ml./min. The temperatures of both solutions were 0.5 deg./sec. The departure from linearity of the maintained a t 90 f 5" and the rate of addition was controlled heating rate was less than 5% above 100°K. bp adding the C a + +solution dropwise from a heated separatory funnel. The carbonate solution was stirred during the and the temperature variation over the surface of precipitation to maintain reasonably homogeneous distrithe sample was less than 5'K. All samples were butions of the various ions. The impurities added to excited by 35 K.V. X-rays from a Mo tube oper- the aragonite samples were included in the calcium ion soluated a t 20 ma. plate current. For most of the tion since their carbonates usually were insoluble. The Ca(N03)S solution was prepared by dissolving high glow curves a 5 minute excitation period was used purity CaC03 (provided by Johnson-Mathey Company of ++
(1) W. L. Medlin, J . Chem. Phys., SO, 451 (1959). (2) W. L. hledlin, J . Chem. Phys., S4, 672 (1961). (3) W.L. hledlin, Phus. Chem. Solids, 18, 238 (1961).
England) in "0,. The carbonate solution was prepared with high purity Na&OJ (also available from JohnsonMathey Company).
July, 1961
THERMOLUMINESCENCE IN ARAGOKITE AND 11~~1: ESITE
The precipitation of magnesite presents a special problem because the stable forms of MgC08 under normal conditions are the hydrates, Mg2(OH)zC03.3Hz0 and 5Mg0.4C02. 5Hz0. At elevated temperatures nesquehonite, MgCO8. 3HzO can be precipitated and magnesite can be obtained by heating this precipitate to temperatures high enough to remove the water of hydration. However, this method is not acceptable for the present application because the removal of the water molecules ruptures the crystal lattice badly enough to prevent the formation of sufficiently large crystallites of magnesite. A satisfactory method of precipitating well crystallized samples of magnesite a t elevated temperatures and COz pressures has been developed by Jantsch and Zemek.4 A modified version of their procedure has been used here. The method consists of raising the temperature of an acid solution of hfgCl2 and urea under a COZ pressure of several atmospheres. A t elevated temperatures, the urea decomposes to form NHa and CO, which raises the pH of the solution sufficiently to piecipitate magnesite, the stable form of &COa under these conditions. The precipitation of the hydrated forms a t lower temperatures is prevented by the acidity of the solution. The impurity ions to be included in the magnesite lattice were coprecipitated by adding them, in appropriate concentrations, to the blgC1, solutions. The samples were precipitated a t 220" under 60 atmospheres of COZpressure in a 1 liter autoclave. It was possible to include f i v ~samples in the autoclave chamber by using 35 ml. Pyrex test-tubes filled to about 70% of their volume with the MgClrurea solution. In order to obtain sufficient quantities of sample under these conditions it was necessary to use concentrations of 0.018 g./ml. Mg++, 0.013 g./ml. urea, and 0.7% HCL. The solutions were protected from contamination by loose-fitting glass covers on the sample tubes. The autoclave was filled to about 30% of its volume with water to provide thermal contact with the walls. At 220" the 3097,, fill was not enough to raise the water level above the tops of the sample tubes so that there was no danger of contamination from this source. Under these conditions the compl te precipitation required 10 to 12 hours. The precipitation is more rapid a t higher temperatures but above 220" the solubility of the Pyrex sample tubes is high enough to contaminate the samples with silicon and other glatjs constituents. It is reasonable to assume that most of the trapping sites and luminescent center? which produce thermoluminescence in aragonite and magnesite are due to the presence of impurity ions. In order to explain the glow peaks in naturally occurring samples of these minerals it is possible to eliminate a number of impurities either because they are not likely to serve as activators or because they are not normally found in natural samples. 411 impurity ions with only one possible valence sta1,e are eliminated for the first reason5 and all of the rare earth elements can be disregarded for the second reason. On ithis basis the following impurities have been investigated: P b + + , Zn++, Cd++, Sb+++, Co++, X i + + , Fe++, S n + + , B i + + + , Cu+, Li+, Al+++, Ag+ and Mn++. Each of thlsse ions was included in the lattice of synthetic aragonite and magnesite samples by the coprecipitation methods described earlier. The inclusion of anion impurities mras not considered since they appear to be unimportant in the carbonate minerals. The effects of cation and anion vacancies were investigated by adding Sn4+ and .P20T4- ions, respectively. It is reasonable to assume that these tetravalent ions introduce cation and anion vacznries to compensate for the charge differences involved but there i q no direct evidence that either ion is included in the aragonite or magnesite lattice. The addition of these ions did not affect the thermoluminescence of either aragonite or magnesite. Of the impiirities mentioned above, M n + + was the only ion found to be an activator of thermoluminescence in either aragonite or maqnesite. Figure 1 shows the glow curves or some synthetic ardgonite samples containing various concentrations of M n + + and in Fig. 2 the results for magnesite are illustrated. In amgonite the M n + + activator accounts for two prominent g!ow peaks a t I80 and 250°K. All of the thermoluminescence is confined to temperatures below 300°K. which is not surprising since aragonite is converted t o calcite (at a tcmperature dependent rate) above 400°K. (4) G. Jantseh and F. Zemek. Radez Rundschau, 3 , 110 (1949). ( 5 ) R. Ward, J . Phus. Cham., S T , 773 (1953).
1173
I
200
IO0
400
300
TEMPERATURE
IN
EQO
DEGREES K.
Fig. 1.-Glow curves for some synthetic aragonite samples containing various concentrations of Jfn ++.
r
IO0
200
3cQ
500
100
TEMPERATURE
IN
600
DEGREES K.
Fig. 2.-Glow curves for some synthetic magnesite samples containing various concentrations of Jfn
++.
0
= 1000 i.0005
az Js:0
"
WOP
0004
MOLE0006 FQbCTlON I COO8Mn".
0010
w1z
< 1/ , L
Fig. %-Efficiency of thermoluminescence for the 180°K. glow peak due to M n + +in aragonite. The theoretical curve was computed from equation 1for z = 1000 and y = 0.0005.
The two prominent glow peaks are preceded a t lower temperatures by a more or less continuous level of emission which is roughly proportional in intensity to the peak heights. The effects of annealing a t elevated temperatures have also been investigated. The glow curves for natural samples of aragonite and magnesite were unaffected hy this treatment but it was found that the glow peaks were measurably en-
W. L. RIEDLIS
1174
T'ol. 63
4 and the accompanying theoretical curves were computed from the expression for an isolated activator ion
0
0
0302
OW6
om4
MOLE
""0
OOOB
00
0019
2
FRACTION M n t *
Fig. 4.-Efliciency of thermoluminescence for the 250°K glow peak due to &In++in aragonite. The theoretical curve was computed from equation 1 for z = 1000 and y = 0.0035
i o 030t!c
0
0 20
3005
0015 0020 W25 MOLE FRACTION M n * + ,
0010
0030
0035
0040
Fig. 5.-Efficiency of thermoluminescence for the 230°K. gloiv peak due to M n + +in magnesite. The theoretical curve was computed from equation 1 for z = 200 and y = 0.0005.
!:::Iq ;
043
p d 030
ozo 0 0
A-
0005
00 i
DO 0
0020
0025
0030
0035
0040
MOLE F R A C T I O N Mn++
Fig. [j.-E%ciencv of thermoluminescence for the 480°K. glow peak due to Mn in magnesite The theoretical curve was computed from equation 1 for z = 200 and y = 0.0005. ++
hanced in the sjnthetic aragonite samples. There was no effect in the synthetic magnesite samples. The aragonite samples were annealed for several hours a t 110-120" which is about the maximum allowable to avoid conversion to calcite. The magnesite samples were annealed for several hours at 450" which is just below the range of decomposition to MgO. The r e d t s of annealing a t elevated temperatures are in accordance with those observed for calcite and dolomite, which have bean interpreted on the basis of localized distortions removed by heating. The effect is presumably not observed in the magnesite samples prepared a t elevated temperatures and pressures because distortions of this type are removed during growth.6 Since natural samples are unafiected by annealing it appears that the distortions have been removed in this case a t the ambient temperature of the earth's crust over geologic times. The two glow peaks due to Mn+" in aragonite are sufficiently separated t o determine the relative efficiency of thermolumineecence for each of them as a function of impurity concentration. These results are plotted in Fig. 3 and (6)
\V L, Jlecllin, d .
Chem. Phvs., 81, 943 (1960).
whcre 7 is the efficiency of thermoluminescence, c is the molar concentration and z and y are parameters characteristic of the spacing between impurity ions and the cross sections for trapping and recombination.? In magnesite the presence of M n + + accounts for tTvo prominent glow peaks at 230 and 480°K. and a t least three minor peaks at 340, 380 and 620°K. In general the glon peaks in magnesite are broader than those in any of the other carbonates, probably because the electron traps are spread over a range of energies in this case. The efficiency of luminescence for the two prominent glow peaks in magnesite is plotted in Fig. 5 and 6 along with the theoretical curves. The quenching properties of Fe, Co and S i have been ne11 established in both calcite and dolomite and similar effects are to be expected in aragonite and magnesite. The effects of these impurities as well as C U + ~Al+++ , and Be+" whirh sometimes art as quenchers have been investigated by adding increasing concentrations of each along with a constant amount of Mn'+. The manganese concentrations were chosen to correspond approsimately to the optimum levels (500 p.p.m. for aragonite and 1500 p.p.m. for magnesite) eo that small fluctuations would not affect the gloiv peak intensities appreciably. The largest variations in >In+- content for all of the samples was less than 100 p.p.m. Fe \vas added in both the 2+ and 3+ states but it was impossible to add the divalent ion without including some of the trivalent ion also. The results shoxed that in aragonite, Fe-+, Co+- and S i + ' inhihited the ;\In-+ luminescence whereas in magnesite only Co++ and S i + + arted as quenchers. It should he noted that for verv low concentrations Co++ enhances the M n + - liiminrscence in magnesite. In both cases F e + + - 41++-, V u + - and R e + + had no effects on the glow peaks duc to Mn-+. Some representative results are shown in Fig. 7 and 8 for aragonite and Fig. 9 for magnesite. The results are plotted as relative efficiency of thermoluminescence as a function of the quenching-ion concentration for the 250°K. glow peak in aragonite and the 230°K. peak in magnesite. Similar results were obtained for the glow peak at 180°K. in aragonite and at 480'K. in magnesite. -411 of the impurity concentrations for the activator and quencher ions in synthetic samples were determined by colorimetric methods. This technique offers several advantages in this case. All of the impurities t o be determined ( A h , Fe, Co and S i ) are transition elements which form strong color complexes and since both aragonite and magnesite are very soluble in acid solutions it is possible t o determine concentrations of only a few p.p.m. m-ith good accuracy. Furthermore, the difficultv of interference from other impurities is eliminated hecause the samples were of high piiriti- except for the added activator oi quencher ions. The procedures for all of the ions involved here already have heen developed for calcite1 and dolomite.* The decay of phosphorescence measured a t constant temperatures near a glow peak provides information about the electronic transitions involved in the trap emptying and recombination processes. The decay curves for all of the principal gloiv peaks due t o Mn '+ in aragonite and magnesite have been measured and found t o be of the form ,
A
where b and m are constants. This form of decay has been observed for calcite, dolomite and anhydrite3 and can be interpreted as being characteristic of a second-order mechanism.* A first-order process would result in an exponential decay but it can be shown that a proper combination of first-order decay curves would result in a decay having the form of equation 2 . 9 Therefore the decay curves could possibly be interpreted as indicating a first-order decay process from a distribution of trapping levels. Some measured values for the parameters b and m are given in Table I for the 250°K. peak due to h h + + in (7) P. D. Johnson and F.E. Williams, i b i d . , 18, 1477 (1950). (8) J. Saddy, J. Phys. Rad., 20, 890 (1959). (9) E. I. Adirovitch, i b i d . , 17, 705 (1966).
aragonite and the 230 and 480°K. peaks due to M n c + in magnesite. The resiilts show that b increases with escitation time whereiis m remains approximately constant. The effect of temperature cannot be determined over any appreciable ranges because of interference between neighboring glow peaks (cf. Fig. 1 and 2) except for the region above the 250°K. M:n++peakin aragonite.
TABLE I \rALL-l:S
OD ?'HE P.4RAbIETERS
b
ASD
m
FOR ISOTIiERblAL
D E C A Y IX A R A G O N I T E A S D ~ l A G N E S I T E
Sample
Glow
Excitation
Imparity,
peak
t h e
p.p.m.
(OK.)
(see.)
250 250 250 250 250 230 230 180 480
45 45 300 15 300 45 ?I00 45 300
80 l l n + " 80 ?*In++ 80 M n + + 80 > I n + + 80 \ I n + + 260 l I n + ' 260 h l n + + 200 .\In 260 l l n +
-4ragonite Aragonite Aragonite Aragoi ii t e Aragoni tr Magnesite AIagncsitc Alagucxsite RIagi iwitc
"+
+
Temp. (OK.)
m
1 1 1 2 1 1 1 1 0
15
245 273
20 30 25 25 5 5 5 30
273
300 300 250 250 480 480
1 3 :3 1 7 2 3 1 93
The depth of the ielectron trap associated with each peak in the glow icurve usually can be determined graphically from the initial rise i.n emission due to the peak. It can be shown10 that the intensity of emission in this region is approximately proportional to exp( - E / k T ) , where k is Boltsmann's constant, T is the temperature, and E is the trap depth or the activation energy required to remove an electron from the trap. In Table 11, the trap depths measured by this method are given for the 250°K. glow peak due to Sin++ in aragonite and for the 230'K. and 480°K. glow peaks due to >In++ in magnesite. The activation energy associated with the 180"K . peak due to Mn++in aragonite was not measurable by this method becsuse of interference from the more or less constant emission a t temperatures below the peak. The traps responsible for this emission can be emptied by warming the samp1.e to the 160-180°K. range. However, many of these traps are refilled (at the expense of the filled traps associated with the 250°K. glow peak) when the temperature is again lowered t o ;'7"K. by immersion in liquid nitrogen. Phenomena similar to this have been observed in calcite and dolomite as ~vt.11as anhydrite and a mechanisni for explaining it already has been proposed . 3 Incidentally, the traps associated m-ith the 180°K. glow peak are not refilled by thin procedure. A rimilar phenomenon occurs in magnesite for the emission in the i7-150"K. range. The traps associated with this emission can be emptied and refilled a t the expense of the filled traps responsible for the 230°K. glox peak. Honr.ver, the interfrrcnce is much smaller in this case and does not prevent a reasonably accurate determination of the t.rap depth for the 230'K. peak.
TABLE II VAI.CES OF T H E LkC'PI\-ATION FACTOR
I'
E
RGY
F O R SOMI: OF THE 'rR.II'PISG
>Ill
I S .kRAGONITE A N D x I A G S E S I T l ?
Irnliurity,
Sample
-4regonite -4ragonite Magnesite 3lse;nesite M:ignesite 3I:ignesite
ASD FREQUENCY
C E N T E R S 1)I-E T O
p.IJ.111.
Glow peak (OK.)
E (e.v.1
1. O
lo6 3 >: loo IO2 7 X 108
0.16
1U2
1.2
IO9
80 > I n + +
250
0.36
490 IZIn++
250 230
.?A)
!I30 030 50 50
lIn-+ RIn++ .\In-* l\ln+'
480 230 480
Y
(see. -1)
.I
i
Table I1 also contains values for the frequency factor associated with each of the trapping levels and computed from the relationlo
Y
(IO) J. T. Randall and RI. H. F. Wilkins, Proc. Roy. Soe. (London), ISCA, 347 (194E~).
0000 I
00003
00002
,00004
M O L E F R A C T I O N Fa++.
Fig. 7.-Quenching
effect of F e + + +in the presence of Mn" in aragonite.
>: z
w
u W U
W
2
a -I LT W
0 I
0001
MOLE
Fig. 8.-Quenching
0603
0002
F R A C T I O N Co++
OR
NI++,
effect of Co++or N i + + in the presence of .\In++ in aragonite.
where p is the heating rate (0.50°/sec. in this case) and T c is the temperature of the glow peak. In order t o verify the results predicted for natural samples of aragonite and magnesite hy the thermolnminescent properties of the synthetic samples, glow curves were pro. duced for a number of natural specimens of both minerals. In Fig. 10 some representative glow curves for a group of aragonite shell samples collected from various locations are illustrated. The striking similarities hetween these c w w s and those of Fig. 1 demonstrate that A h " + accounts for all of the thermoluniineseence in most natural aragonite. It is significant that the general level of emission of all of the aragonite samples collected was quite low. Spectrographic analyses revealed that this effect resulted from the quenching effect of Fe (found in concentrations ranging from 10 to 50 p.p.m.) and t o the small amounts of manganese present (less than 5 p.p.m. in most samples). In all of the samples of natural magnePite collected the thermoluminescence was negligible. In a few samples there was evidence of the ?rIn'+ glow peaks at 230 and 480" K . (cf. Fig. 2) but in most cases the only measurable thermoluminescence was attributed t o small amounts of calcite or dolomite presrnt in the samples. These results indicate a more or less complete exclusion of manganese in natural magnesite and this was verified by spectro. graphic analyses which showed undetectable amounts ( < 2 p.p.m.) of this impurity.
111. Discussion of Results The results of this investigation have shown that the thermoluminescent properties of naburally
W. L. MEDLIN
1176
T'ol. 65
wrong coordination number to be included readily in the aragonite lattice and is too large to fit into the magnesite structure very well. The results of the efficiency us. concentration curves of Fig. 3-6 indicate that the effects of concentration quenching are considerably different in aragonite and magnesite. The parameter, z. determined empirically from equation 1 for each of the glow peaks due to Mn++ is a measure of this effect. Its value is equal to the number of nearest neighbor cation sites surrounding a Mn++ center which cannot be occupied by another manganese ion without quenching the luminescence.' Therefore, a z of 1000 for the aragonite glow peaks indicates that the thermoluminescent transitions due to a Mn++ center generally are quenched when another manganese ion is located as close as 5 or 6 nearest neighbor distances. Similarly, the z of 200 for the magnesite peaks indicates a quenching radius of 2 or 3 nearest neighbor distances. Thus the distortions produced in the crystal field by the substitution of a Mn++ ion extend over a larger region in aragonite than in magnesite. The isothermal decay curves for aragonite and magnesite have the same form as those observed I 0001 0002 0003 wo4 for calcite, dolomite and anhydrite. The form MOLE FRACTION GO++ OR Ni++. given by equation 2 is characteristic of a secondorder process but the behavior of the parameter b Fig. 9.---Quenching effcct of Co++or Ni++in the presence of h h + + in magnesite. as a function of excitation time is in disagreement with the behavior predicted by this model. AS shown in Table I, b generally increased with * excitation time whereas the inverse relation is to be e x p e ~ t e d . ~ The values reported in Table I1 for the frequency factor v deserve some comment. Since v is essentially the frequency with which an electron attempts to escape from a trapping site its value cannot exceed the frequency of atomic vibration sec.-l). In most crystals for which values have been reported, v falls in the range 10fi-lO'O see.-' l1 and most of the values reported here are within this range. However, the value of lo2 TEMPERATURE I N DEGREES K. obtained for the 23OoK. peak in magnesite is unFig. 10:-Glow curves for some natural aragonite samples. reasonably low and it is doubtful that this result is occurring aragonite and magnesite are subject to valid. Since the values for v are calculated simple interpretations. I n both cases the thermo- from the graphically determined values of E , it luminescence appears to be due solely to the pres- appears that the method for determining E is not ence of divalent manganese. Lattice defects such valid in this case. Incidentally, the determination as ion vacancies evidently are not important in of E is only possible by this technique when the glow peaks are isolated and are due to a single diseither crystal[. At optimum manganese concentrations (500 crete trapping level. Because of the complexity p.p.m. in aragonite and 1500 p.p.m. in magnesite) of the magnesite glow curve (cj'. Fig. 2 ) it is quite the respective levels of thermoluminescent intensity possible that either of these conditions is violated. are of about the same order of magnitude for aragoIV. Conclusions nite and magnesite (cf. Fig. 1 and 2). This level is about one order of magnitude lower than the All of the important thermoluminescent properthermoluminescence due to the optimum Mn++ ties of aragonite and magnesite arc due to divalent concentrations in calcite or dolomite. In natural manganese. The presence of &In++ results in samples of these minerals, however, the calcite and glow peaks a t 180 and 25OOK. in aragonite and a t dolomite luminescence is several orders of magni- 230 and 480°K. in magnesite. The presence of tude greater in general than the emission from Co++ or Ni++ quenches the h h + " luminescence aragonite and the thermoluminescence in natural in both minerals. In aragonite, Fe++ quenches the magnesite is usually negligible. These results are RSn++ luminescence more effectively than Co mostly due to the effective exclusion of manganese from aragonii,e and magnesite, a result which is not (11) G . F. J. Garlick and A F. Gibson, Proc P h y s . Soc. (London). surprising in view of the fact that Mn++ has the 6 0 8 , 574 (1948). I
I
++
July, 1961
ELECTRON IMPACT SPECTROSCOPY OF ETHYLENE SULFIDE
or Ni++ but in magnesite it has no appreciable effect. Because of the differences in ionic radii and coordination numbers, A h + + is not easily substituted into either the aragonite or the magnesite lattice. Therefore, its concentration in natural samples of these minerals is exceedingly small, particularly in magnesite where it is generally undetectable. As a result of this, the intensity of thermoluminescence is generally very low in aragonite and usually negligible in magnesite. The presence of iron in most aragonite samples is a further cause of reduced emission. The thermoluminescence found in most natural magnesite samples general1.y is due to the presence of some calcite or dolomite. Consequently, magnesite is of little interest in interpreting the thermoluminescence of rock samples except as its presence reduces the intenaity of emission from other minerals by acting tis n more or less inert material. Aragonite is not i.ery important either although the &In++ glow peaks usually are measurable in this case.
1177
Since most natural magnesite samples contain negligible concentrations of Mn++ and since all of the aragonite thermoluminescence is confined to temperatures below 350°K., neither of these minerals is useful in age measuring applications. The isothermal decay of phosphorescence has the same form for all of the glow peaks in aragonite and magnesite as for anhydrite, calcite and dolomite. The form of the decay curve can be explained on the basis of a second-order process involving transitions through the conduction band of the crystal. Furthermore, a discrepancy in the predicted behavior of one of the decay parameters which was reported for the other minerals also has been observed in aragonite and magnesite. The activation energy, E , and frequency factor, v, for the traps associated with the various glow peaks are about the right order of magnitude except for the 23OoK. peak in magnesite. For this peak, the value of v is several orders of magnitude smaller than any values previously reported.
ELECTRON IMPACT SPECTROSCOPY OF ETHYLENE SULFIDE AXD ETHYLENIRIINEl B Y EbfILIO G A L L E G O S AND
w.
ROBERT KISER
Department of Chemistry, Kansas State University, Manhattan, Kansas Receaued Janunry 5, I961
The appearance potentials and relative ahundances determined with a time-of-flight mass spectrometer are reported for the principal positive ions in the mass spectra of ethylene sulfide and ethylenimine. The probable ionization and dissociation processes consistent with the computed energetics are given. Molecular ionization potentials are calculated using the equivalent orbital method and are compared to the observed ionization potentials of 9.94 f 0.15 e.v. for ethylenimine and 8.87 f 0.15 e.v. foy ethylene sulfide. A comparison of the fragmentation patterns and dissociation processes is given for ethylene oxide, ethylene sulfide and ethylenimine.
Introduction We have determined the mass spectral cracking patterns and the appearance potentials of the principal ions from ethylenimine and ethylene sulfide, and compared these with the information reported previously for ethylene oxide.2 Consist’ent with the probable ionization and dissociation processes and with the ionization and appearance potentials obtained, the heats of formation of the various principal ions of ethylene sulfide and ethylenimine have been determined. The mass spectral cracking pattern of ethylene sulfide and ethylenimine are reported : that for ethylenimine compares favorably with that listed in the A.P.I. tables of inass ~ p e c t r a . The ~ appearance potential data of ethylenimine and ethylene sulfide and the mass spectral cracking pattern of ethylene sulfide are newly reported. (1) This work was supported in part by the U. S. Atomic Energy Commission, under Contract No. AT(ll-1)-751 with Kansas State University. Portion of a dissertation t o be presented by E. J. Gallegos t o the Graduate Schocl of Kansas State University in partial fulfillment for the degree of Doctor of Philosophy in Chemistry. Presented a t the 139th Meeting of the American Chemical Society, St. Louis, h40.. March 21-30, 1961. (2) E. J . Gallegos and R. W. Kiser, J . Am. Chem. Soc.. 83, 773 (1961). (3) “Mass Spectral ]>eta,” American Petroleum Institute Research Project 44, National Bureau of Standards, Washington, D. C.
Experimental The general features of the Bendix model 12-100 time-offlight (TOF) instrument used in this study have been described.2 The resolving power of this instrument is ( M / A M ) E 140, as determined from the “5% peak width,” A H / H = 0.1, A h / H = 0.001 and l/I%.4 The sample of ethylenimine was obtained from Matheson, Coleman and Bell, and was used as received. It was statrd to have a minimum purity of 98%. Dr. R. P. Ciula of these laboratories provided the samples of ethylene sulfide; these were synthesized from ethylene carbonate and potassium thiocyanate a t 115-120O and the samples were distilled over a t 52”. The ethylene sulfide was used immediately after preparation to avoid any polymer formation in the sample. No significant impurities were observed in the mass spectra of either ethylenimine or ethylene sulfide. Gas-liquid partition chromatographic analysis of ethylene sulfide on tri-ntolyl phosphate revealed no impurity peaks; thereforr, it was estimated that the ethylene sulfide had a purity > O D 5 mole yo. Mass spectra were obtained for nominal electron energies of 70 e.v. The voltage scale was calibrated by using miutures of krypton or xenon with the compound being investigated, and by subsequent comparison of the observed ionization potential of the rare gases with their known spectroscopic values.5 The extrapolated difference method of obtaining ionization and appearance potentials has been described.2 Ionization potentials also were determined (4) J. H. Beynon, “Mass Spectrometry and its Applications t o Or ganic Chemistry,” Elsevier Publishing Co., Amsterdam, 1960, p p 51-54. (5) C. E. Moore, “Atomic Energy Levels,” Natl. Bur. Standards Circ. 467, Val. 3, 1958.
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