2684
NOTES
the smaller mean activity coefficient. This rule cannot be extended to include ammonium salts, however. The mean activity coefficients of the salts in water decrease in the order LiCl > NaCl > NH4Br > KCl > NH4C1 > RbCl > CsCl. It is clear that NH&1 should be more comparable to KCl if the “rule” had wider significance. Although the trends are consistent with the initial decrease and subsequent increase of activity coefficients as ionic strength increases the order and the magnitudes find no simple explanation. The order is not in keeping with a lowered dielectric constant of aqueous electrolyte solutions as proposed by Hasted, et aL;9 the order for depressing the dissociation would have to be LiCl > NaCl > KC1 RbC1. Rationalization in terms of structure-making and structurebreaking ions is possible but this approach lacks in predictive capabilities.lo One correlation which deserves further exploration concerns hydration of the
-
ions. The less the “free” water (all water not bound to ions) the lower the degree of formation of sulfate. The free water concentration, FC)”, is given by TC, hCs - Cw’. T C is~ the total water concentration, h is a total hydration number for salt of concentration CS, and C,’ is the water bound by the proton, sulfate, bisulfate, and ammonium ions. For the ternary systems of this study T C is~ not known. The values for binary salt-water solutions, however, do permit estimation of FC, values which lead to a correct sequence if spectroscopic estimates of h are used, i.e., h of 4 for LiC1, 3 for SHdC1, and 5 or larger for the other halides of larger ionic radii.
Acknowledgments. This work was supported by the National Research Council of Canada. (9) H . B. Hasted, D. Nl. Ritson, and C. H . Collie, J . Chem. P h y s . , 16, l(1948). (10) H . Chen, Ph.D. Thesis, University of Waterloo, Waterloo Ontario, Canada, 1971, p 103.
NOTES Viscosity Independence of the Half-Width of the vl(A1) Raman Line of Sulfate Ion
by D. E. Irish” and R . C. Meatherall Department of Chemistry, The University of Waterloo, Waterloo, Ontario, Canada (Receiued A p r i l 6 , 1971) Publication costs borne completely by The J o u r n a l of Physical Chemistry
The liquid state is characterized by random molecular motions. Transitions from one equilibrium position to another, hindered partial rotations, and collisions are occurring with a high frequency. The mean lifetime of a molecule betn-een random reorientations has been linked to changes in the half-widths of Raman lines and infrared lines of liquids. Studies of pure organic liquids at different temperatures and of organic mixtures reveal a relationship between half-width and the reciprocal of v i s c ~ s i t y . ~ - Few ~ width studies have been performed on aqueous electrolyte solutions. Concentration narrowing has been reported for alkali metal nitrite solutions and the inferred encounter rate constant increases with the solubility of these highly soluble salts.* Both specific and nonspecific dependences have been observed for the width of vibrational lines of alkali metal nitrate^.^ T h e Journal of Physical Chemistry, Vol. 76, KO.1 7 , 1971
The changes in width resulting from collisions and hindered motions generally do not exceed 10 cm-l. These processes account for most of the width of vibrational lines of molecules in the liquid phase providing chemical processes are absent.6 The latter include ultrafast proton transfer between hydronium ion and a base. Broadenings of more than 30 cm-’ result if the mean lifetime of the species is of the order of sec.’ I n recent work on the bisulfate-sulfate equilibrium a proportionality has been found between the broadening of the 981-cm-l symmetric stretching vibration of sulfate ion and the total hydronium ion concentration p r e ~ e n t . ~The , ~ data have provided strong support for an interpretation in terms of ultrafast proton transfer and insight into the mechanism of the transfer process. It is important, in view of the literature cited above, to ensure that this interpretation is not in error (1) A. V. Rakov, T r . F i z . l n s t . A k a d . S a u k S S S R , 27, 111 (1964). (2) I. I. Kondilenko, V. E. Pogorelov, and K . Khue, O p t . Spectrosc., 28, 367 (1970). (3) S. Higuchi, S. Tanaka, and H. Kamada, S i m o n Kagalcu Zasshi, 89, 849 (1968), Chem. Abstr., 70, 7706 (1969). (4) D. E. Irish and M . H. Brooker, Trans. Faraday Sac., 67, 1916 (1971). ( 5 ) D. E. Irish and A. R. Davis, Can. J . Chem., 46, 943 (1968). (6) K. S. Seshadri and R. N . Jones, Spectrochim. Acta, 19, 1013 (1963). (7) E. Grunwald, Progr. P h y s . Org. Chem., 3 , 317 (1965). (8) D. E. Irish and H. Chen, J . P h y s . Chem., 74,3796 (1970). (9) H. Chen and D. E. Irish, ibid., 75,2672, 2681 (1971).
NOTES
2685
because of a contribution to the broadening from viscosity. The half-width of the 981-cm-1 line of sulfate ion (the same line studied in the proton transfer experiments) has been investigated for 1.2 M ammonium sulfate solutions containing different amounts of glucose, used to vary the viscosity. Ideally a colorless substance was desired which, when added in trace amounts, would increase the viscosity substantially. Neither glycerol nor Kelzan, a water soluble polymer supplied by the Kelco Chemical Co., were satisfactory. Aqueous glucose solutions have two broad bands located at 1070 and 900 cm-l. It was possible to obtain a good 981-cm-' line profile between these two. Five solutions were prepared. Each was 1.2 M in ammonium sulfate and contained sufficient glucose to provide viscosities of 2.0, 11.5, 85.0, 274.0, and 500.0 cP, respectively. The viscosity was measured in a Brookfield small sample chamber viscometer, jacketed for temperature control to 25 0.1". Solutions were contained in a Raman cell fitted with a water jacket and were maintained at 25 f 1". Spectra were excited by the 435.8-nm mercury line and obtained on the Cary 81 spectrophotometer. A slit width of 10 cm-l was used. The half-widths were measured, both manually and with the aid of a computer routine for the study of line shape.8 For each solution a width of 14.5 =k 0.5 cm-I was found. Within a wave number the halfwidth of the symmetric stretch of sulfate does not change when the viscosity of the medium changes from 2 to 500 cP. This independence is expected. The depolarization ratio of the symmetric stretch of a tetrahedral molecule is zero and the polarizability tensor is isotropic; in this case rotatory motions have no effect on the width of lines.' Any anisotropy, induced by the environment in the liquid phase, will be small.'O I n light of these results it is believed that the Raman line broadening data for sulfuric acidgand bisulfatess require no correction for viscosity.
*
(10) W.F. Murphy, M. V. Evans, and P. Bender, J . Chem. Phys., 47, 1836 (1967).
Experimental Section Hot 38Clmas produced by means of the 37C1(n,y)38C1 reaction using the 1-Mw reactor of Washington State University. Samples of the desired reactant were sealed in Vycor ampules along with small amounts of Ar, 02,and dichloroethylene. All liquids were degassed in the vacuum system prior to use. Gases were obtained from Matheson Co. and used without purification. Dichloroethylene, used as a scavenger, was obtained from Eastman Co. Reagent grade CCI, was used directly. Product analysis was by conventional radiogas chromatography using columns of either silicon GE SF-96 or silicon DC 550 on firebrick. Adsorption of halocarbons by stopcock grease is a frequent problem in this work, particularly if the compound being determined is present only at tracer levels. To eliminate this difficulty, the inlet system of the gas chromatograph was constructed using Teflon stopcocks. (1) (2) 86, (3) (4)
Replacement Reactions of Hot Chlorine Atoms in Chlorofluoromethanes
R. Wolfgang, Progr. React. Kinet., 3 , 97 (1965). C. M. Wai, C. T . Ting, and F. S. Rowland, J . Amer. Chem. Soc., 2525 (1964). C. M. Wai and F. 9 . Rowland, J . Phya. Chem., 71, 2752 (1967). C. M. Wai and F. S. Rowland, ibid., 72, 3049 (1968).
(5) C. M. TVai and F. S. Rowland, (1968).
by S. C. Lee and C. 0. Hower* Department of Chemistrg, University of Idaho, iMoscow, Idaho (Received October 14, 19YO)
used with great success to study the inertial and steric factors that affect hydrogen-atom reactions. There is now considerable interest in extending these studies to hot halogen reactions in order to build a general model of the factors controlling the reactivity of monovalent chemical species. Recoil studies of chlorine atoms were initiated by Wai and R o ~ l a n d ~and - ~ by Spicer and Wolfgang.8 Recoil fluorine has received relatively more a t t e n t i ~ n . ~Spicer, Todd, and Wolfgang have measured yields of hot fluorine replacement products in fluoromethanes'" and hot chlorine replacement products in chloromethanes," and discuss the trends observed in terms of steric factors and a "translational inertial" effect. We report here the results of measurements made on the absolute yields of hot replacement products in chlorine-atom reactions with chlorofluoromethanes. These results represent the first systematic study of C1 for F replacement reactions and the first comparison of C1 for F with C1 for C1 replacements in the same molecule. Yield patterns are similar to those reported by Spicer, et ai., but some significant differences are also observed.
89849
Publication costs borne completely by The Journal of Physical Chemistry
In the last decade, the reactions of translationally hot tritium atoms, produced by nuclear recoil, have been
J. Amer. Chem. Soc.,
90, 3638
(6) C. M. Wai and F. S. Rowland, i b i d . , 91, 1053 (1969). (7) C. M . Wai and F. S. Rowland, J . Phys. Chem., 74, 434 (1970). (8) L. Spicer and R. Wolfgang, J . Chem. Phys., 50, 3466 (1969). (9) See for example (a) C. F. McKnight, N. J. Parks, and J. W. Root, J . Phys. Chem., 7 4 , 217 (1970); (b) T . Smail and F. S. Rowland, {bid., 7 4 , 1859 (1970). (10) L. Spicer, J. F. J. Todd, and R. Wolfgang, J . Amer. Chem. Soc., 90, 2425 (1968). (11) L. Spicer and R. Wolfgang, ibid., 90, 2426 (1968).
The Journal of Physical Chemistry, Vol. 76, N o . 17, 1971
