J. Phys. Chem. 1980,84, 3655-3660
3655
Long-Range Structuring of Water by Quartz and Glass Surfaces as Indicated by the Infrared Continuum and Diffusion Coefficient of the Excess Proton Nod K. Roberts" Cheimistry Department, University of Tasmania. Hobart, Tasmania, Australia 7001
and Georg Zundel Physikalisch-ChemischesInstitut, Universitat Miinchen, 0-8000Munchen 2, Federal Republic of Germany (Received November 5, 1979; In Final Form: April 23, 1980)
The absorbance of the infrared continuum of 1M HC1 between parallel quartz plates and absorbed in porous quartz (pore-sizerange 4-15 pm) shows a depression of -14% in the case of porous quartz. It is shown both theoretically and experimentally that the lowered absorbance >inthe case of porous quartz is not due to weldge-shaped layers of liquid in the porous disks. The intensities of some CH stretch bands for several organic liquids were the same in thin films and absorbed in porous quartz of the same effective thickness, indicating that optical effects are not responsible for the lowering of the infrared continuum of 1M HC1. The lowering is most probably due to long-range structuring of dipolar water molecules by the large surface area of quartz. Approximately 0.3 pm of 1 M HC1 in contact with the quartz surface does not contribute to the absorbance. The structured dipolar water molecules increase the electrical field at the easily polarizable H band of the H5O2+ groupings in which the proton fluctuates and decrease the fluctuation frequency and the associated IR continuum. Tracer diffusion coefficients for the hydrogen ion in supporting electrolytes of the alkali halides from accurate rotating disk electrode measurements and from the sintered glass diaphragm cell method (pore size range 5-15 p m ) lend support to the infrared measurements above. The glass diaphragm cell method gives low limiting values for the diffusion coefficient of the hydrogen ion, -13-14% lower than the Nernst limiting value at infinite dilution. This lowering can be explained in terms of -0.3 pm or 1000 moleular diameters of water in contact with the glass surface which is not available for the Grotthus diffusion of the hydrogen ion. The structuring envisaged is not of the strong short-range electrostatic type, but of a weak but long-range cooperative structuring of H bonded water molecules, which is in some way initiated by the surface. Only a relatively minor structuring is required to increase significantly the electrical field experienced by the proton fluctuatingin H50z+groupings with easily polarizable H bonds, which in turn leads to a lowered continuum and a decreased diffusion coefficient.
Introduction The structure of water and the mobility of the excess proton in water at surfaces is of particular importance in biological systems. For some years Drost-Hansenl has maintained that the structure of water is modified a t surfaces, and in some cases to a distance of thousands of molecular diameters. Recently2 we have shown how infrared measurements of the continuum observed in acid solutions can be used to detect the long-range structuring of 1 M HC1 a t a quartz surface and the accompanying reduction of the eiccess proton mobility. In this paper we present additional evidence to show that optical effects, in particular wedge-shaped layers, cannot be responsible for the depression of the IR continuum of 1 M HC1 in quartz pores. A comparison of the diffusion coefficients of the hydrogen lion from accurate rotating disk measurements and from the glass diaphragm cell method also lends support to infrared results. Infrared Measurements The method of' detecting long-range surface effects consists of measuring the absorbance of the continuous absorption observed in acid and base solutions beginning at 3200 cm-l and extending to smaller wavenumbers. It has been shown3 that the continuum is due to the H50,+ groupings in the case of acids and the H,02- grouping in the case of bases. The phenomenon is not confined to acids and bases and ham been observed whenever there is a grouping with a hydrogen bond in which a potential well with a double minimum or a flat broad potential well is present. Such cases have been observed in aqueous and 0022-3654/80/2084-3655$0 1 .OO/O
nonaqueous solution^.^ Furthermore, it has been demonstrated that such H bonds are extremely easily polarizable. The polarizability of such H bonds is about two orders of magnitude greater than the usual polarizabilities, and hence they interact strongly with the environment, for example, by indluced dipole interactions with ions and with dipole fields of the solvate and solvent molecules and particularly with each other. The energy surfaces of the easily polarizable hydrogen bond in H502+ becomes strongly deformed by these interactions. As the strength of these interactions shows a broad distribution, a continuity of energy level differences occurs which is observed as a continuum in the IR spectra. On the other hand, crystals containing H5O2+,for example, give broad bands4 in the IR spectrum instead of a continuous absorption, because the H5102+ions are held in rigid crystalline lattice and do not experience the fluctuating random electric fields of a solution. The presence of the continuum with aqueous acids indicates that protons are fluctuating between two boundary structures I and I1 (Figure l). If the continuum decreases because of some external field, this means that the hydrogen bond becomes polarized, the proton lingering time is greater at one of the two water molecules in the H50zf grouping, and the proton fluctuation frequency is d e ~ r e a s e d .Consequently ~ any influence which modifies the normal fluctuating structure of water containing, for example, H50z+groupings should also influence the continuous IR absorption. If the influence structures the water causing an asymmetrical environment of the H502+groupings, then the continuum should decrease, and if, on the other hand, the influence 0 1980 American Chemical Society
3650
The Journal of Physical Chemistty, Vol. 84, No. 26, 1980
1
Flgure 1. Fluctuation of proton between boundary structures I and 11.
5 30-
n
I
b-
DEPENDEYCE OF A 3 5 3 R B A N C E OF ZONTINLUM AT 2560rm.' 3N EFFECTIYE T H I C K N E S S OF lhl HCI
Y
3000 2500 WAVENUMBER (cm-11
F m b e t r e e n 30
(i
el
5
con
plotPa
x
Flgure 2. Spectra of water (a) and 1 M HCI (b), effective thickness 25.5 f 0.5 pm absorbed in porous quartz (pore size 4-15 pm).
- 1-
e t Y e e n PQ101 e1 q.lc 12
p10ie5 0
AbS-rhfb
1
quo'
1
p 3 w s of
i - 1 5 ~ d a r~n e t e r
renders the normal bulk structure of water containing the
H502+groupings more random, then the continuum should i n ~ r e a s e . Such ~ effects have been observed on adding electrolytes to aqueous solutions of strong acids.6
Experimental Section The porous quartz disks (pore range 4-15 pm) for the infrared measurements were ground to a thickness of between 100 and 130 pm as described previously.2 The effective thickness of the absorbed water and 1M HC1 was determined by weighing the absorbed water and 1M HC1 and from the diameter of the disk (30 mm). The thickness of films between parallel optically flat quartz plates was determined by using 25- and 50-pm spacers and measuring the interference patterns with only air present, using the relation d = 1000(m
+ 1)/2(i9 - pk)
where d = thickness in pm, m = number of interference maxima between the ith and kth interference maxima, and Pi and Dk = wave numbers of the ith and kth interference maxima, respectively. The thickness of the parallel layers between silicon plates separated by spacers was determined from the absorbance of the benzene band at 1958 cm-l with an extinction coefficient of 0.926. In the original paper2 the result for a separation of 48 prn is plotted incorrectly and should be 0.68 absorbance (A). This alteration reduces the slope of the plot to 0.0140 A/pm.
3
10
31
20 EFFECTIVE THICI(NES8
3'
'0
SO
1 M HCI (,urn
Flgure 4. Dependence of absorbance of continuum at 2560 cm-' on effective thickness of 1 M HCI: (0)film between parallel sllicon plates; (X) film between parallel quartz plates; (0) absorbed in porous quartz (pore size 4-15 pm).
A special holder was used in all cases to avoid evaporation. A Perkin-Elmer Model 580 ratio-recording spectrophotometer at an ordinate expansion of 20X was used to record the spectra of water and 1 M HC1 absorbed in porous quartz. On the expanded scale the transmittance is reliable to 0.4%. Results and Discussion Figure 2 shows the IR spectra of water and 1 M HC1 absorbed in porous quartz. The transmittance of the continuum alone for 1M HC1 as a film between parallel silicon and quartz plates and absorbed in porous quartz is shown in Figure 3. The shapes of tahe transmittance curves are the same but the transmittance of continuum is greater for 1M HC1 absorbed in porous quartz. The absorbance of the continuum at 2560 cm-l, where water has almost zero absorbance, as a function of the effective thickness of 1M HC1 is given in Figure 4. The slope of absorbance of the continuum vs. effective thickness of 1 M HC1 was 0.0140 A/pm for parallel films between silicon and quartz plates and 0.0120 A/pm for absorption in po-
The Journal of iPhysical Chemistry, Vol. 84, No. 26, 1980 3857
Long-Range Structuring of Water
TABLE I APa 0.100 0.200 0.300 0.400 0.500
----
Figure 5.
b-
__.
r
Absorbance of wedge-shaped layer.
If one uses the re1,ations dy = dx/tan 4 and b = 2d/tan 4 and integrates firom 0 to 2d, it follows that 2d 0
:= e-E sin h ( E ) / E
The measured extinction EM = - In rM. Hence E M = E - In (sin h(E)/E),i.e., the extinction of a wedge, EM, is less than the extinction of a corresponding parallel layer, E , by [In sin h ( e ) / E ] , Consequently, if the 1 M HC1 absorbed in the porous quartz is equivalent to a wedge rather than a parallel layer, a lower absorbance would be observed. Such an effect would be more prclnounced in very thin layers of porous quartz where the distribution of channels in the quartz would no longer ble statistically equivalent to a parallel layer. Electron micrographs showed that the porous quartz was in fact quartz in which there were channels of diameter ranging from 4 to 15 pm. The theoretical absorbances for parallel and wedge-shaped layers calculated from eq 1 are given in Table I. Even though the experimental values are in reasonable agreement with thlose for wedge-shaped layers, it is per-
AexpC 0.17 0.25 0.33 0.4 2
a A, = absorbance of parallel layer. A w = absorbance of wedge-shaped layer of same width and mean Aexp = absorbance of 1 M HC1 in porous thickness. quartz estimated from Figure 2. Note that A = E/2.303 where E = extinction (see eq 1).
TABLE I1
row quartz of pore size range 4-15 pm. The lower absorbance of 1 M HCl in porous quartz at 2560 cm-l is ascribed to a polarization of the H502+ groupings by their local environments, i.e., a structuring of the water molecules by the quartz surface. I t was pointed out in the original paper2 that it was unlikely that optical effects were responsible for the decreased absorbance of l M HC1 absorbed in porous quartz as the shape of the continuum in porous quartz and between quartz plates was identical (Figure 3). Optical effects are known to be sensitive to the wavelength. Also it was difficult to imagine an optical effect which could be responsible for a lower absorbance of 1 M HC1 absorbed in porous quartz. However, there is such an effect and it will be discussed fully in the following section. Effect of Wedge-Shaped Layers on the Absorbance. The following derivation7 demonstrates that a wedgeshaped layer has a lower absorbance than a parallel layer. Both layers are of the same width, and the average thickness of the wedge is equal to the thickness of the parallel layer. For a parallel layer the Lambert-Beer law is applicable, Le., 7 = e-E where r = transmittance and E = extinction. Consider a wedge of average thickness d and width b (Figure 5). We have for each section of width dy, from the Lambert-Beer Law, that the measured transmittance drMis equal to
AWb 0.096 0.182 0.287 0.343 0.413
-
material
absorbn refracfor refractive tive inCH stretch 25.4 index, dex band, cm-' pm n20D n2,:,,
chloroform -3020 benzene -3070 chlorobenzene 3070 1 M HCl continuum measured at 2560 quartz
-
a
0.42 0.79 0.40 0.35
1.445 1.498 1.523 1.333 (H,O)
N.A.' 1.475 N.A.' -1.43
(HZO)
1.458
Not available.
fectly clear that the layers in the porous quartz cannot be wedges. For example, at an absorbance of 0.5, Figure 2 shows that the parallel layer has a thickness of -35 pm. Therefore for this layer to give an absorbance of 0.413, the layer of 1 M HlCl in the porous quartz would have to be equivalent to a wedge varying in thickness from 0 to 2d (Figure 3), i.e., from 0 to -70 pm. From the original experimental results it is also extremely unlikely that the lower absorbance of 1 M HC1 in porous quartz is the result of wedge-shaped layers. Firstly, two porous disks containing almost the same average thickness of 1 IM HC1, i.e., 31.6 and 31.8 f 0.4 pm, gave the same absorbance of 0.38 (Figure 4). It would be most unlikely for these two disks to have the same effective wedge-shaped layer of 1 M HC1. It is much more likely that the layerie of HC1 in both disks are essentially equivalent to parallel layers. Secondly, passing the IR beam through different sections of the same disk did not alter the absorbance, which is further confirmation that the layer of absorbed 1 M HCl is equivalent to a parallel layer in the range of porous quartz thicknesses which we have studied. Effect of Porous Quartz on IR CH Stretch Bands of Some Organic Liquids. To ascertain further whether optical effects could be responsible for the observed experimental results,,several organic liquids were absorbed in porous quartz and suitable CH stretch bands in the infrared were cornpared with those of the same liquids as thin films between quartz plates. To compare these results with those for the IR continuum of 1M HC1, it is desirable (a) that the infrared refractive index of the organic liquid should be similar to that of 1 M HC1, so that any reflection losses at liquidlpore interfaces are constant, and (b) that the overall intensity of the band being measured should be similar to that of the HC1 continuum in an equivalent thickness of porous quartz. Unfortunately data for the IR refractive index of organic liquids are scanty (for example, see ref 8). Benzene is one of the few liquids for which data are reasonably complete. Using an extrapolation described by Bauer and F a j a n ~ , ~ we estimated the refractive index of benzene at 2560 cm-l.
3658
The Journal of Physical Chemistty, Vol. 84, No. 26, 1980
Roberts and Zundel
TABLE I11 effective thickness of some porous quartz disks, ,um
liquid
from from weight weight of of liq- from extinction uid ab- coefficient of water disk sorbed IR band absorbed
chloroform
A 41.5
benzene
B C
chlorobenzene
C
D
i
0.5 26.0 i 0.5 24.0? 0.5 23.9 i 0.5 37.0 i 0.5
40.5 i 0.5 (- 3020 cm-') 26.3 i 0.5 ( - 3 0 7 0 cm-') 24.3 i 0.5 ( - 3 0 7 0 cm-') 24.1 i 0.6 ( - 3 0 7 0 cm-') 37.5 i 0.5 (- 3 0 7 0 cm-I)
40.7 f 0.5 25.5 i 0.5 23.6 i 0.5 23.6 i 0.5 36.0 i 0.5
Table I1 summarizes the relevant properties of the three organic liquids chosen and water and quartz. The refractive index for water in the IR region is discussed by Eisenberg and Kauzmann.lO Although it was not possible to completely satisfy both criteria (a) and (b), the experimental results shown in Table I11 are fairly convincing evidence that optical effects are not responsible for the lowering of the IR continuum of 1M HC1 by porous quartz. It is clear from Table I11 above that the porous quartz has little or no effect on the IR bands of the chloroform, benzene, and chlorobenzene; i.e., optical effects are negligible. The results also confirm the effective thickness of the porous disks used in the study. The absorbed liquid is, therefore, statistically equivalent to a parallel layer, and the lowering of the absorbance cannot be due to wedgeshaped layers as discussed previously. Minimum Thickness of 1 M HC1 in Contact with Quartz Surface Which Does Not Contribute to the Absorbance of the Continuum. It is possible to estimate the minimum thickness of 1M HC1 in contact with a quartz surface which does not contribute to the absorbance of the continuum. Consider Figure 4. A parallel film between plates has a slope of 0.0140 A/pm and that for a film absorbed in porous quartz is 0.0120 Alpm; Le., a 14% depression of the absorbance is observed in porous quartz. If one assumes that a mean diameter of the channels in the porous quartz is 10 pm, for every square meter of solution of thickness 10 pm the number of channels is ('/lo X and the surface area of each channel is 4(10 X 10 X 10-l2)m2 for rectangular channels; i.e., the total internal surface area of all channels per square meter of porous X 104)2 x 4(102 X 10-l2) = 4 m2. For quartz equals a 10-pm film a 14% depression of the absorbance corresponds to 1.4-pm thickness which does not contribute to the absorbance. Since the surface area of quartz in contact with the 1 M HCl has increased from 2 X 1 m2 for two quartz plates to (2 t 4)m2 for the porous quartz between quartz plates, the minimum thickness of nonabsorbing 1 M HC1 per surface (Le., 1 m2) equals 1.4/4 = 0.35 pm. Limiting Diffusion Coefficient of the Hydrogen Ion in Water from the Rotating Disk and Glass Diaphragm Methods. The values obtained for the tracer diffusion coefficients of the hydrogen ion from the rotating disk electrode and from the glass diaphragm cell (pore size 5-15 pm) also suggest that the lowering of the continuum of 1 M HC1 in porous quartz is due to a structuring of the water molecules adjacent to the quartz surface. In earlier publication^'^-^^ we discussed the difference in the limiting diffusion coefficient of the hydrogen ion from polarography and the glass diaphragm methods. The
E
l
5'
I
3
05
10 CONCENTRAT!OY [mol I
'
15
20
Figure 6. Tracer diffusion coefficient of the hydrogen Ion in potassium chloride solutions. Glass diaphragm cell method: (X) ref 26. Rotating disk electrode method: (0) ref 19; (A) ref 20; (+) ref 21.
-
value from the glass diaphragm cell method was much lower ( 13%) than that from polarography. However, the theoretical equations describing the diffusion of an ion to a growing mercury drop are open to debate, especially over the value of the constant A in the corrected Ilkovic equation id = 697nD1/2Cm2/3t1/6(1 + ml/zm-1/3t1/6) in which id = mean diffusion current in microamperes, C = concentration of depolarizer in mmol L-l, D = diffusion coefficient of the depolarizer in cm2 s-l, m = rate of flow of mercury in mg s-l, n = number of faradays per mole of electrode reaction, t = drop time in seconds, and A is a constant. A has been given variously as 17,1424,1539,16and 45.1. l' On the other hand the theoretical equations governing the diffusion of an electroreducible ion to a rotating disk electrode are much more reliable and give excellent agreement with nonelectrochemicalmethods. Opeker and Beran18have pointed out the accuracy of the determination of diffusion coefficients using the rotating disk electrode. The most recent determinations for the tracer diffusion coefficient of the hydrogen ion have been reported by Glietenberg et al.,19 Gostisa-Mihelei6 et al.?O and Wetsema et a1.21 These results for the tracer diffusion coefficient of the hydrogen ion in KC1 are shown in Figure 5. Both Opekar et al.lSand Wetsema et alaz1remarked on the poor agreement with the results from the glass diaphragm in dilute solution. One of the present authors drew attention to this fact some years ago.l1-l3 LandsbergZ2compared earlier results from electrochemical and the glass diaphragm cell methods. The plot of his results also shows that the electrochemical results extrapolate to the correct limiting value for the diffusion coefficient of the hydrogen at 25 "C, viz., 9.31 X cm2 s-l, whereas those for the glass diaphragm cell24extrapolate to a lower value of 8.13 x cm2s-l. One of the present a ~ t h o r s ' l -w~as ~ the first to suggest an explanation in terms of structured water at the surface of the glass pores, though he envisaged a more rigid structuring than that suggested later in this paper. Most of the results for the diffusion coefficient of the hydrogen ion were calculated from a corrected form of the LevichZ3equation given by Gregory and RiddifordZ4 nFCD2/3v-1/6~1/2 id = 1.6126 + (D/~)'.~~(0.5704) where w = rate of electrode rotation, v = kinematic viscosity of the solution, D = diffusion coefficient, and the other symbols have their usual meaning.
The Journal of Physical Chemistty, Vol. 84, No.
Long-Range Structuring of Water
Figure 6, showing the most recent and reliable results for the hydrogen ion, illustrates clearly that the results from the glass diaphragm cell method extrapolate to 8.13 X compared with the limiting value of 9.31 X cm2 s-l determined fro:m the limiting ionic conductance of the hydrogen ion via ithe Nernst relationship I)H+' =
26, 1980 3659
I
LICI
x
Glass Oiaphragrn cell [ p o r e size 5-15!.)
o
aototlng disc electrode
RT(XH+),/F
where (AH+), = equivalent ionic conductivity of the hydrogen ion at infinite dilution. The principle of the glass diaphragm cell method is to confine the diffusion process to the capillary pores of the sintered glass diaphragm. If the average value of the diffusion coefficient, D, with respect to the_concentration range prevailing at the time considered is D(t) (indicating that it is also a function of time), then the time average of D ( t ) ,D , is given by25
where c1 and c2 are the concentrations of the diffusing ion in the lower and upper compartments, initially, and c3and c4 are the values at time t. The cell constant, P, is given by P (A/O(l/Ui + l / u z ) where A = total effective cross section of the diaphragm pores, 1 = effective average length along the diffusion path, u1 = volume of lower compartment, u2 = volume of upper compartment. Since D is proportional to the differential diffusion coefficient, D, the calculated values of D are proportional to the cell constant P. The cell constant is determined by allowing potassium chloride solutions to diffuse through the diaphragm. Siince the diffusion coefficient of the potassium chloride solutions is known from absolute methods, P may be calculated. While P may be the same for electrolytes which diffuse by a hydrodynamic mechanism, it is not the same for solutions containing the hydrogen or hydroxide ions which diffuse also by the Grotthus mechanism. This seems likely as the diffusion coefficients of cations other than the hydrogen ion extrapolate to the expected Nernst limiting value^.",^^-^^ The term in the cell constant P which is expected to change in going from normal electrolytes to acids and bases is A, the cross-sectional area of the diaphragm pores. A certain thickness of the solution near the glass surface is structured and thurl reduces the Grotthus contribution by increasing the electrical field at the H bond where the proton fluctuates between boundary structures I and I1 (Figure 1). The Grotthus contribution amounts to -90% of the total diffusion coefficient at infinite dil ~ t i o n The . ~ limitling value DH+O(Figure 5 ) is 8.13 X 10" cm2 s-l compared with 9.31 X cm2 s-l for the Nernst value and that obtained by extrapolating the results for the rotating disk electrode, i.e., a depression of 13%. If the average pore size is 10 pm for sintered glass, pore range 5-15 ym, and if one assumes rectangular pores (cylindrical pores give the s a m e results), a 13% depression means that the effective cross-sectional area, A, of the pores is reduced from (10 X 10) X m2to 87 X m2 or that the edge of the rectangular pore is reduced in width from 10 to 9.33 p, which is equivalent to a minimum of 0.34 pm per surface. The limiting value in LiCl solutions is DH+O= 7.93 >c cm2s-I, which leads to a value of 0.36 pm for the structured layer. These values are in remarkably good agreement with the IR results for quartz, indicating 0.35 pm per surface. Drost-Hansenl has estimated a thickness of 0.2 pm for N
0'5
1c 1 5 CONCENTRATION [mol I-']
2 0
Flgure 7. Tracer diffusion coefficient of the hydrogen ion in lithium chloride solutions. Glass diaphragm cell method: (X) ref 26. Rotating disk electrode method: (0)ref 19.
Pyrex from conductivity measurements on capillaries containing dilute potassium chloride solutions. The reason fior the identical DH+values above 1M KC1 supporting electrolyte for both the glass diaphragm cell and rotating disk electrode methods is as follows. At low concentrations of supporting electrolyte the sintered glass diaphragm reduces the diffusion coefficient of the hydrogen ion by long-range cooperative structuring of the water dipoles and by strong short-range electrostatic forces of the K+ and C1- ions. The strong electrostatic forces of the ion extend over only a few molecular diameters. As the concentration of the electrolyte increases, more and more water and H5O2+ groupings come under the influence of the strong short-range electrostatic forces of the ions. At 1M KC1 supporting electrolyte the average distance between the K+ and C1- ions is lo-' cm, i.e., ca. four water molecules. Consequently, with both methods above 1 M KC1 the prime effect is the short-range electrostatic effect of the ions on tlhe H5O2+ groupings, and the DH+values by both methods isre almost identical. It is only at concentrations less than 1 M that the long-range cooperative structuring of the water dipoles by the glass surface is evident. The difference between the two curves below 1 M is a measure of this long-range cooperative structuring effect by the glass surface. At infinite dilution only the long-range structuring effect of the glass surface is present. This explanaiion is borne out by a comparison of the results for DH+values in KC1 and LiCl supporting electrolyte (Figures 6 and 7). The DH+values from the glass diaphragm cell and rotating disk electrode methods become identical at a concentration at 0.5 M LiCl and at 1.0 M KC1. The reason for this difference is that the much smaller Li" ion has a higher charge density and exerts a stronger electrostatic effect on the intervening water molecules and lH502+groupings. Consequently the cooperative structuring of the water molecules is destroyed at a lower concentration of LiC1.
-
Conclusion The long-range structuring of water at quartz and glass surfaces as indicated by IR and electrochemical diffusion measurements does not require that the water be rigidly structured as olbserved for molecules within a few monolayers of a surface. The electrical fields necessary to reduce the fluctuation of the proton between boundary structures I and I1 (Figure 1)do not have to be very large.5 A slight reorientation of the dipolar water molecules within 0.3 pm of the surface, Le., -1000 molecular diameters of water, can produce a field of sufficient magnitude to reduce the continuum significantly. It has been calculated that an
3000
The Journal of Physical Chemistry, Vol. 84, No. 26, 1980
icelike structure would produce a field of 1.5 X lo* V cm-l a t a central water molecule.30 A field of an order of magnitude less than this value would reduce the absorbance of the continuum to a very low value5 and also lower the Grotthus component of the diffusion coefficient significan tly.
References and Notes (1) J. A. Schufle, C. T. Huang, and W. Drost-Hansen, ColloMInterface Sci., 54, 184 (1976). (2) N. K. Roberts and G. Zundel, Nature (London), 278, 726 (1979). (3) 0. Zundel in "The Hydrogen Bond, Recent Developments in Theory and Experlments", P. Schuster, G. Zundel, and C. Sandorfy, Eds., North Holland Publlshlng Co., Amsterdam, 1976, Chapter 15. (4) M. Williams in "The Hydrogen Bond, Recent Developments in Theory and Experiments", P. Schuster, G. Zundel, and C. Sandorfy, Eds., North Holland Publishing Co., Amsterdam, 1976, Chapter 14. (5) A. Hayd, E. G. Weideman, and G. J. Zundel, J . Chem. Phys., 70, 86 (1979). (6) D. Schioborg and G. Zundel, Can. J . Chem., 54, 2193 (1976). (7) A. Hayd, Dlssertation, Sektion Physik, University of Munich, 1975, p 92. (8) J. Timmermans, "Physico-Chemical Constants of Pure Organic Compounds", Vol. 11, Elsevier, Amsterdam, 1965. (9) N. Bauer and K. Fajans in "Physical Methods of Organic Chemlstry", A. Weissberger, Ed., 2nd ed., Intersclence, New York, Chapter 20, 1949. (10) D. Eisenberg and W. Kauzmann, "The Structure and Properties of Water", Oxford University Press, London, 1969, p 199 et seq.
Roberts and Zundel (11) N. K. Roberts and H. L. Northey, J . Chem. SOC.,Faraday Trans. 7, 68, 1528 (1972). (12) N. K. Roberts and H. L. Northey, Nature(London),237, 144 (1972). (13) N. K. Roberts, Nature (London), 249, 594 (1974). (14) H. Strehlow, 0. Madrich, and M. von Stackelberg, Z . Elektrochem., 55, 244 (1951). (15) H. Matsuda, Bull. Chem. SOC.Jpn., 36, 342 (1953). (16) J. J. Lingane and 8. A. Loveridge, J . Am. Chem. Soc., 72, 438 (1950). (17) R. S. Subrahmanya, Can. J. Chem., 40, 289 (1962). (18) F. Opekar and P. Beran, J . Electroanal. Chem., 69, 1 (1976). (19) D. Glietenberg, A. Kutscher, and M. Stackelberg, Ber. Bunsenges. Phys. Chem., 72, 562 (1968). (20) B. Gostisa-Mihelei& W. Vielstich, and H. Heindrichs, Ber. Bunsenges. Phys. Chem., 76, 19 (1972). (21) B. J. C. Wetsema, H. J. M. Mon, and J. M. Los, J. Electroanal. Chem., 68, 139 (1976). (22) R. Landsberg, W. Gelssler, and S. Muller, Z . Chem., 1, 169 (1961). (23) V. G. Levich, Acta Physicochim. URSS, 17, 257 (1942). (24) D. P. Gregory and A. C. Riddiford, J. Chem. Soc., 3756 (1956). (25) R. A. Robinson and R. H. Stokes, "Electrolyte Solutions", 2nd ed., Butterworth, London, 1959, p 253 et seq. (26) L. A. Woolf, J. Phys. Chem., 64, 481 (1960). (27) R. A. Roblnson and R. H. Stokes, "Electrolyte Solutions", 2nd ed., Butterworth, London, 1959, p 317. (28) R. H. Stokes, S. Phang, and R. Mills, J . Solution Chem., 8, 489 (19791. (29) K. R. Harrls, H. G. Hertz, and R. Mills, J. Chim. Phys. Phys.-Chim. Biol., 75, 391 (1978). (30) D. Eisenberg and W. Kauzmann, "The Structure and ProDerties of Water", Cl&endon Press, Oxford, 1969, p 110.
