2263
COXTINUOUS ABSORPTION SPECTRA OF HALOGESS AN) ISTERHALOGEK COMPOUNDS
Z z + l / D T_=_ 1.1 _ _is still consistent, 1.18 is the firm value for DP,/DP,. The relatively minor effect of ____ various values for DP,,l/DP, on D P , / D P , is shown by the comparison for sample 5-50 shown in Table V. _ I
Table V Resulting
Assumed _ _
D P , +JDP.
DPJDP, (es. 9)
1.3 1.2 1.1 1.0
1.24 1.21 1.18 1.15
Conclusions The comparisons in Table IV sh0.w that information on the molecular weight distribution of a linear polymer can be obtained from an analysis of its cross linkingsolubility behavior without assumptions as to the particular form of the distribution, if the chain scission pa-
rameter is small. Apparently, _ _ -there is some tendency toward overestiniation of DP,/DP, for narrow distributions and underestimation for broad distributions. This may reflect some systeniatic error in measuring S , because of curvature, or more likely, it may mean that the simple, first-approximation equations are unable to compensate completely for the effect of chain scission. However, the discrepancy is generally small and the numerical agreement quite satisfactory. It - _ _ should be noted also that DP,/DP, and D P J D P , are obtained from quite different portions of the gel curve and thus constitute independent tests of the data. -
_
.
Acknowledgments. The author is grateful to the Yational Science Foundation for predoctoral fellowship support during 1966-1959. Thanks are due also to Dr. R. E. Skochdopole and Dr. H. W. il4cCormick of the Dow Cheniical Company, to Professor Brymer Williams and Professor D. W. McCready for their many helpful suggestions through the work, and to Dr. L. M. Hobbs and Dr. J. A. Manson whose interest originally led to the study.
The Continuous Absorption Spectra of Chlorine, Bromine, Bromine Chloride, Iodine Chloride, and Iodine Bromide
by Daniel J. Seery and Doyle Britton Department of Chemistry, University of Minnesota, Minneapolis 14, Minnesota
(Received March 16, 19Sg)
The continuous absorption spectra for gaseous Clz, Br,, BrCl, ICl, and IBr between 220 and 600 mp litre reported. The experimental data have been fitted to theoretical curves of the type suggested by Sulzes and Wieland. The parameters for these curves are given.
Introduction In the course of shock tube studies of the interhalogen compounds and the dissociation of the halogens, we have found it necessary to know the extinction coefficients for IC1, BrCl, Brz, and C1, in the visible and
near-ultraviolet. Since the literature values for IC1 and BrCl are incomplete O r appear to be incorrect, we have determined the continuous absorption spectra of these compounds, as well as IBr, between 220 and 600 mp. Br2 and Cla have been redetermined in order to Volume 68, Number 8 August, 1964
DANIELJ. SEERYAND DOYLE BRITTON
2264
calculate consistent values for BrC1, which only exists in equilibrium with its elements. The earlier work will be described in the Discussion. The decadic extinction coefficient, E , is defined by log (ioli) = eel, where z o / i is the ratio of the incident light intensity to the intensity transmitted through l cm. of c moles/l. of the compound in question. With Clz and Brz this is unambiguous; with the interhalogens the possibility of disproportionation to the elements must be considered and allowed for.
Experimental Chemicals. Matheson Coleman and Bell Co. Clz stated to be 99.5% pure had been earlier found to contain excessive COz (up to loo/,) and was purified by liquefying the CL and repeatedly pumping off the COz rich vapors above the liquid until the infrared absorption a t 2350 cm. -l indicated less than 1% COe. Allied Chemical Co. Bra was used without further purification. Mallinckrodt analytical reagent grade Iz was used without further purification. Fisher "pure" IBr was used without purification. BrCl was prepared by mixing various proportions of Clz and Br2 and allowing the mixture to equilibrate. IC1 was prepared by the method of Cornog and Karges.l The freezing point was found to be 26.76' compared to the literature value of 27.19", but it was very sharp. Measurements. All measurements were made on a Cary Model 11 recording spectrophotometer using 10em. quartz cells. A stopcock and ground glass connector was cemented to the cell with ,4piezon W for the Brz and C1, experiments. This was found to be too reactive with the interhalogens and Kel-F grease was substituted. The ground glass parts had been well ground before being used and a minimum of wax or grease was necessary. Reaction with the grease or wax was shown to be negligible in the arrangements used by the constancy of the spectra over several hours. Pressures were measured on a Pyrex spiral manometer.2 All measurements were made a t room temperature, 25
-f
2O.
Chlorine. Four measurements of the spectrum of Clz, a t concentrations of 1.47 X 1 0 - ~ to 4.57 X 10+ M , were made. The weighted averages of these measurements are reported in Table I . Bromine. Three measurements of the spectrum of Brz, at concentrations of 0.86 x lop3to 1.32 X M , were made. The weighted averages are reported in Table I. Bromine Chloride. Xine measurements were made of the spectrum of BrCl. To each of the Brz samples mentioned above was added approximately half, once, and twice the amount of Clz as Brz originally present. The Journal of Physical Chemistry
Table I : Extinction Coefficients us. Wave Length Wave length,
____ Extinction coefficients,a mole-'
IBr
17.5 18.8 16.3 11.5 7.7 4.2 2.5 I .4 1.3
55.8 92.5 115.1 113.3 92.2 63.7 40.3 24.6 15.9
9.4 14.9 26.7 43.7 56.1 60.4 55.2 44.0 32.5
0.2 0.8 2.9 10.0 23.3 47.6 81.4 119.0 148.9
3.9 10.0 23.6 45.4 71.4 94.9 107.4 106.3 93.7 76.6
12.0 10.5 9.6 8.6 8.1 9.2 13.9 23.0 36.3 49.6
20.8 14.1 5.6 3.8 4.0 6.2 10.9 18.2 31.5
165.0 165.5 155.5 140.8 127.4 117.1 108.4 101.5 93.2 82.9
60.0 47.9 39.6 34.3 30.2 26.8 23.0 18.6 14.2 10.5
64.5 75.5 83.9 92.7 101.6 109.0 111.4 107.0 95.0 77.0
53.5 83.0 117.1 153,5 188.1 222.8 257.6 290.6 313.5 318.2
70.7 46.2' 33.5 26.3 20.7 16.1 11.9
7.4 . . .b
8.8
... ... ...
59.6 42.9 30.0 20.9 14.9 11.3 9.0 7.4 5.5 4.6
303.2 269.6 224.5 176.6 136.9 95.8 71.2 52.0 38.1 29.6
Cla
Bra
BrCl
220 230 240 250 260 270 280 290 300
... ... 0.2 0.3 0.6 2.3 7.0 17.0 31.4
... ... .'. ...
310 320 330 340 350 360 3 70 380 390 400
48.3 61.8 67.0 61.8 49.6 34.4 21.8 12.9 8.6 5.0
410 420 430 440 450 460 470 480 490 500
3.5 2.6 1.9 1.4 0.9
510 520 530 540 550 560 570 580 590 600
...
... ...
... ...
1. om. -I--
IGI
mCt
... ... ...
...
... , . .
, . .
... ... ...
... ... , . .
... ... ...
6.1
...
... ... ...
... ...
8.8
* The uncertainty in the values given is about 0.5 except for IBr where it is -2.5. Discrete absorption of Brz begins a t 512 mp and causes an increased uncertainty in the values for Brz and BrCl a t longer wave lengths.
I n each of these mixtures the BrCl concentration was calculated using the equilibrium constant3 of 8.01 for the reaction Brz (31%= 2BrCl. About 40 min. was allowed for equilibrium to be attained. Judging from
+
(1) J. Cornog and R. A. Karges, J . Am. Chem. Soc., 54, 1882 (1932): (2) J. D. Ray, Rev. Sci. Instr., 32, 600 (1961). (3) W. H. Evans, T. R. Munson, and D. D. Wagman, J . Res. Natl. B u r . Std., 55, 147 (1955).
CONTINUOUS ABSORPTION SPECTRA OF HALOGEXS AKD INTERHALOGEX COMPOUNDS
the reproducibility of the spectra after the mixing period this was sufficient time. The observed optical density was assumed to be given by log (io/%)
=
Z(EB=~CB~,
+
EciZCci,
+
CB~C~CB~C~)
and the value of EBGI calculated therefrom. The good agreement among the various samples would indicate that the equilibrium constant used is correct. The actual BrCl concentration ranged from 0.62 X to 2.33 X M . The weighted averages of the ext inctioii coefficients are given in Table I. Iodine Chloride. Three measurements were made of the spectrum of IC1 a t concentrations between 0.97 X and 1.74 X M . The reported value, 3.41 X of the disproportionation constant3 for the reaction 21C1 = IZ Clz would indicate that no correction need be made for Iz and Clz concentrations, that this reaction could be ignored. This was checked by three more runs in which Clz was added to the IC1 and the observed optical density assumed to be
+
log (ioli) =
+
~(EICICICI tci,Ccip)
The agreement (h1% or less) between the values of EICI determined in the presence and absence of Clz showed that the disproportionation was, indeed, negligible, and also that there is no significant formation of IC&. The weighted averages of e101 for the runs using pure IC1 are listed in Table I. Iodine Bromide. Four measurements were made of the spectrum of IBr a t concentrations between 0.17 X and 0.25 X M . As with IC1 the disproportionation equilibrium constant132.08 X was small enough to be ignored, This was confirmed by four runs with added Brz, which gave the same ( f1% or less) values for € 1 ~ ~ The . lower concentrations used here (limited by the lower vapor pressure of IBr) makes the accuracy of these measurements less. The weighted averages of the runs using pure IBr are listed in Table I.
2265
violet and by Gibson and Ramsberger* in the visible. We agree with the former, but are consistently much higher than the latter (approximately 35% a t the maximum). No previous work on IBr has been reported. All of the preceding references are to measurements in the gas phase. Gilliam and Morton9 have measured all of these compounds in solution in CCl,, and if the BrCl results are corrected for the disproportionation of BrCI, the maxima in solution are roughly 50% higher than the corresponding maxima in the gas phase. Buckles and have measured the extinction coefficients of Br2, Iz,and IBr in solutions in acetic acid, carbon tetrachloride, and trifluoroacetic acid. The intensity of the absorption for a given compound varies depending upon the solvent used; for all three solutes the spectra in trifluoroacetic acid were roughly identical with the gas phase spectra. In view of the variation of the intensity depending upon the solvent and phase, it would be of interest to re-examine the claim of Bayliss and Rees,ll denied by Evans,12 that the extinction coefficient of gaseous Br, changes with the pressure in the presence of inert gases. Our interest in these data has been to use them to predict high temperature values of the extinction coefficients. Sulzer and Wieland13have developed a simple theory for the continuous absorption spectra of diatomic molecules which says that the spectrum can be resolved into Gaussian peaks and that each peak can be described by
e(w,T)
I=
ern(T) exp( - [(w - wo)/Aw(T) 12)
crn(T)== Emo[tanh(hcwv/2kT)]’/’ Aw(T)
=
Awo[tanh (hcwV/2kT)]-”’
where E ( W , T ) is the extinction coefficient a t w cm. and T’K., wv is the vibrational frequency of the molecule, and emol wo, and Awo are the maximum, position, and half the mean width of the Gaussian peak at 0°K. Values
Results (4) G. E. Gibson and N. S. Bayliss, Phys. Rev., 44, 188 (1933).
The measured extinction coefficients are presented (5) L. T. M.Gray and D. W. G. Style, Proc. R o y . SOC.(London), in Table I. The curve for C1, has been determined preA126,GO3 (1930). (6) A. P. Acton, R. G. Aicken, and N. 9. Bayliss, J. Chem. Phys., 4, viously by Gibson and B a y l i ~ s . ~Our results are in 474 (1936). close agreement with theirs. The curve for Brz has (7) J. L. Binder, P h y s . Rev.,54, 114 (1938). been determined twice previously. We agree reason(8) G. E. Gibson and H. C. Ramsberger, Phys. Rev.,30, 598 (1927). ably well with the results of Gray and Style15but our (9) A. E. Gilliam and R. A. Morton, Proc. Roy. SOC. (London), results are consistently higher than those of Acton, A124, 604 (1929). (10) R. F. Buckles and J. F. Mills, J . Am. Chem. SOC., 76, 6021 Aicken, and Baylisse (approximately 10% higher a t (1954). the maximum). The curve for BrCl has only been determined previoudy between 240 and 270 m ~ . (11) ~ N. S. Bayliss and A. L. G. Rees, Trans. Faraday Soc., 35, 792 (1939). Our results agree with this work. The curve for IC1 (12) D. F. Evans, J . Chem. Phys., 23, 1425 (1955). has been determined previously by Binder’ in the ultra(13) P. Sulzer and K. Wieland, Helv. Phys. Acta, 25, 853 (1952). Volume 68, Number 8 August, 1964
DANELJ. SEERYAND DOYLEBRITTON
2266
Table I1 : Parameters for Gaussian Peaks a t 0°K. Fit from the Data of Table I Gas
Clz
Brt BrCl
IC1
IBr
fmo
00
Awo
71.6i0.7 90.1f2 . 9 204.2 f 1 . 4 25.1 f 0 . 5 121.2 i 0 . 4 21.3 f 0 . 2 50.7 =t1.1 100.3 f 0 . 9 9.4’f 0.3 137.8 f 0 . 4 169.8 f 7 . 1 288.0 f 6 . 5 78.9 f 1 . 4
30456 f 24 20452 f 59 24159 f 42 21952 i 59 26768 i 17 43898 f 64 20818 f 15 22598 f 23 30775 f 69 40986 f 15 19715 i 20 20951 f 34 37289 f 74
3085 i 31 1582 f 51 2102 f 32 1945 f 64 2537 i 19 5023 f 75 1229 f 24 2804 f 13 2407 f 92 4332 f 27 1132 f 30 2211 f 16 3848 f 77
a The weak peak in IC1 was found by fitting the strong peaks on either side t o Gaussian curves and then taking the differences between observed and calculated values and treating these differences as observed data.
of w v are known from spectroscopic measurements and are14: Cla, 561.1 cm.-’; Brz, 323.2; BrC1, 443.1; IC1,
The Journal of Physical Chemistry
382.2; IBr, 267.4. The other parameters are determined from the experimental curves. We have determined these parameters for all of the experimentally observed peaks in our spectra. The fit has been made by least-squares calculations for one or two peaks a t a time, depending on whether the peaks are overlapped or not. These calculations were made using a FORTRAY program on the Control Data 1604 computer of the Numerical Analysis Center of the University of Minnesota. The results are shown in Table I1 together with estimated standard deviations for the parameters. It should be emphasized that the peak heights listed here are for 0°K. and will not correspond to the experimental values at room temperature.
Acknowledgments. We wish to thank the U. S. Army Research Office (Durham) for their support of this work. We also wish to thank nh. E. G. Saettler for making preliminary measurements of some of these spectra. (14) “JANAF Thermochemical Tables,” The Dow Chemical Co., Midland, Mich., June, 1960.
