NOTES
349 1
Equilibrium Constant for the Fractionation
of Deuterium between Ice and Water by Bragi Arnason Science Institute, University of Iceland, Reykjasck, Iceland (Received A p r i l 7, 1969)
In the first decade after the discovery of deuterium several experiments were carried out to determine the fractionation of hydrogen isotopes between ice and water accompanying the change from liquid to solid state. A bibliography up to 1953 is given by Ingerson.' Most of the deuterium determinations referred to by Ingerson were made by precise measurements of the density of water samples. However, these measurements gave inaccurate and conflicting results, so the authors do not even agree whether deuterium concentration is higher in the liquid or the solid state. Since 1953 several authors determined the fractionation constant
experimentally as well as theoretically. Table I shows the results obtained by various authors during this period. 4-s
Table I: The Values of the Fractionation Constant of Deuterium for Ice and Water Obtained by Several Authors Since 1955" Fractionation constant Theoretical Experimental
Authors
Weston4 Posey and Smith& Kuhn and Thurkaufd Merlivat and Nief7 O'NeiP Craig9 Present work
1.0192 i 0.0002 1.0186
1.0211 & 0.0007 1.0171 rt 0.0005 1.0235* 1.0195 1.0195' I.0208 i 0.0007
'
' Both theoretical and experimental values. Calculated from measurements of Olaolid-va,,or = 1.132 and aliquid-vapor = 1.106. ' NaCl solution of 4 o / chlorinity. ~ ~
beIow zero by pumping the refrigerant through it. The ice crystal freezes to the inflow end of the copper tube and an ice layer starts to grow in such a way that the ice front moves with approximately constant rate from one end of the copper tube to the other. At the same time the already formed ice layer steadily becomes thicker. The rate at which the ice grows can be controlled by adjusting the temperature and flow rate of the refrigerant. When the ice layer had become approximately 2 mm thick at the inflow end of the copper tube and 1 mm thick in the middle, the tube was taken out of the beaker and all water wiped off with a piece of tissue paper. A piece of the ice approximately 1 cm long was broken off at each end of the copper tube and discarded. The remaining ice and a sample of water from the beaker were analyzed in the mass spectrometer. Each ice sample was about 2 ml. The experiment was carried out 24 times. The time taken for the ice layer to grow to 2-mm thickness a t the inflow end of the copper tube ranged between 1 min and 180 min as the temperature of the refrigerant varied from about -5.5 to -0.5'. For most of the experiments the flow rate of the refrigerant was approximately 50 ml/min. The magnetic stirrer was adjusted so that the velocity of the water past the copper tube was 5-10 cm/sec. Sample preparation, method of measurement, and the mass spectrometer are all described by Friedman.2 This is not an absolute determination of deuterium concentration. The measurements are based on two standard water samples S B S I and NBS IA from the National Bureau of standards in Washington which, according to Craig, have deuterium concentrations BNBS I = -47.6% and BNBS IA = -183.3% relative to SMOW (Standard Mean Ocean Water). The results are expressed as 6 = per mill deuterium enrichment (depletion negative) relative to SMOW. Results
Table I1 shows the results obtained from the 24 experiments. Column I gives the number of the experiment. A subdivision a or b means that the ice has been divided into two parts at the middle of the copper tube. Part a is from the inflow end and part b from the outflow end. Column I1 shows the duration of freezing. At least 2 preparations are made from each ice sample for the deuterium measurements in the mass spectrometer.
Experimental Section
A glass beaker containing 2 1. of distilled water was immersed in an ice-water bath. A U-shaped copper tube 16 cm long and 6.5 mm outside diameter was connected to a refrigerating machine and immersed in the distilled water. The water in the beaker was agitated by means of a magnetic stirrer. The refrigerant used was a methanol-water mixture. ' When the water in the beaker has a temperature of 0" a small ice crystal is introduced and the copper tube cooled to
(1) E. Ingerson, Bull. Geol. Soc. Am., 64, 301 (1953). (2) I. Friedman, Geochim. Cosmochim. Acta, 4 , 8 9 (1953). (3) H. Craig, Science, 133, 1833 (1961). (4) R. E. Weston, Geochim. Cosmochim. Acta, 8, 281 (1955). (5) J. C. Posey and H. A. Smith, J . Amer. Chem. Soc., 79, 555 (1957). (6) W. Kuhn and M. ThUrkauf, Helu. Chim. Acta, 41, 110, 938 (1958). (7) L. Merlivat and G. Nief, Tellus, 19, 1, 122 (1967). (8) J. R. O'Neil, J. Phys. Chem., 72, 3683 (1968). (9) H. Craig, Trans. Amer. Geophys. U n i o n , 49, 1, 216 (1968). Volume 78. Number 10 October 1969
3492
NOTES
The results are shown in column 111. Column IV gives the mean values for the ice samples. The corresponding water samples are treated in the same manner and the results shown in column V. Only one water sample was taken for the experiments 5-8, but these experiments were done without changing water in the beaker, and no measurable change in deuterium concentration could have occurred by freezing out some 10 ml from 2 1. of water. The same applies to experiments 11-12 and 13-14. In all other experiments a sample of water is taken while the ice is freezing out. The water for experiments 1-4 is taken from the same reservoir and has the same deuterium concentration. The water for experiments 5-24 is taken from another reservoir. The mean values of deuterium concentration for the two types of water listed in column VI are therefore used with the mean values of the ice samples from each experiment listed in column IV to calculate the respective fractionation constants. Column VI1 shows the value of the fractionation constant in each case calculated from the equation
+ &j) (1 + $ ); (1
a =
In Figure 1, a is plotted vs. the duration of freezing for the sample in question. It is obvious from Figure 1 that if the sample is frozen out in only a few minutes isotopic equilibrium is not obtained. From 60 min on, a seems to have reached its equilibrium value. This means that under the present experimental conditions, isotopic equilibrium with water will be maintained in the surface of freezing ice if the rate of freezing is less than 2 mm/hr.
1I 0
20
40
60
80
100
120
140
160
Figure 1. The fractionation constant derived from each experiment plotted against the duration of freezing.
For calculating the final value for the equilibrium constant only ice samples from experiments 16-24 are used, with freezing time from 60 to 180 min or a freezing rate of 0.7-2 mm/hr. The water for all these experiments and also experiments 5-15 is taken from the same reservoir and has the same deuterium concentration. The fluctuations of the last 33 6 values in column V only represent a normal distribution of results from the mass spectrometer. These repeated measurements ensured that the measuring apparatus was functioning properly. The mean deviation for the 25 last 6 values in column I11 shows agreement with the water samples, indicating that equilibrium conditions are the same in all the experiments 16-24, in spite of varying rates of freezing. Standard deviation for a single 6 determination with the mass spectrometer is 1.2°/00. The mean value for the ice samples in experiments 16-24 is 6iee = -43.5 i 0.5°/,0 where f0.5°/,, represents the 95% confidence limit. The mean value for the water samples in = -63.1 f o.4°/00. This experiments 5-24 is gives a = 1.0208 f 0.0007. The 95% confidence limit of f0.0007 does not include possible inaccuracies in the deuterium concentration of our standard samples. These samples have been used for 6 years, but after the present experiment they were compared with new NBS
Table 11: The Results Obtained from the 24 Experiments Described VI awaterv ' / o o
mean of each water type
VI1 a0
1.0189
1 bb
25
2
25
3
30
4
25
T h e Journal of Physical Chemistry
-41.5 -39.6. -41.6 -41.3' -42.0 -41.9 -40.5. -41.3 -42.6 -42.0 > -43.3,
-40.9 -41.7 -41.2 -42.6
180
Duration of freezing rnin
-60.3' -59.4 -58.6 -59.9 -59.4 -59.1 -61.0 -61.6 -59.9 -64.3 -61.5 -61.0 -59.2,
I.0208 1.0199 7
-60.4 1.0204 1.0189
NOTES
3493 ~
~~~~
Table I1 (Continued) IV
I Expt no.
I1 Duration of freezing, min
VI
V
8aoe I O/oo
dwater,
means of eaoh expt
of single measurem.
O/oo
bwatsr, ‘ / o o
mean of each water type
VI I ,a
5
5
-48.6
6
5
-47.7
7
25
-45.2
1.0191
8
25
-44.9
1,0194
9
42
-45.6
10
10
11
14
-45.0 -43.1 ’ -47.0 -44.5 -46.4 > -46.11
-45.0
1.0155 1.0164
-62.t -62.1
-63.4 -63.1 -65.( -64.1 -63.:
1.0187 1.0193
-45.7
1.0186 -63.4 -62.3
12
3
-47.6
13
2.5
-52.2
1.0165 1.0116 -63.9 -63.4
14
1
-54.1
15
30
-44.9
16
60
-44.3
17
65
-43.6
18
68
-43.7
19
85
-43.8
20 ab
85
-44.2
20 bb
85
21
100
22
110
23
140
1* 0201 1.0208 1.0207 1.0206 1.0202 1.0205 1.0222
-42.7
-64.2 -62.3
1.0218
-43.1
24 bb
180
-44.4
b
-63.7 -62.3
1.0194
-42.3
-43.4
+ +
-64.2 -62.0 -62.6 -63.7 -61.0 -61.2 -63.7 -63.1
-63.1
-63.1 -63.9
180
1 aioe/lOOO 1 ~w*t0r/1000’
-63.1 -62.0
-43.9 -42.1 -40.7 ’ -44.2 -44.5 -41.5 ’ -42.1
24 ab
CY=
1.0096
-61.5 -64.2 -63.9 -63.4 -60.7 -62.7
1.0213 1.0210 1.0200
Subdivision a or b means that the ice has been divided into two parts a t the middle of the copper tube.
Volume 78, Number 10 October 1060
3494
NOTES
I and NIBS IA standards sent to us by the IAEA in Vienna. There was agreement between the old and new standards. Actually it is only the ratio between the deuterium concentration of the two standards which enters into the value for a. Should the value for this ratio be changed after repeated measurements, the same relative change should be applied to CY 1.
Table I: Spectra of Surface Species on Cobalt
Adsorbates
----Freauencies. Surface species
Acknowledgments. The author wishes to express his appreciation to Professor Th. Sigurgeirsson, head of the Physics Division of the Science Institute, for his advice and encouragement, and to Mr. Th. Bddlason, of the Mathematics Division, for many fruitful discussions. The author is also indebted to Dr. I. Friedman a t the U. S. Geological Survey for reading the manuscript and offering valuable suggestions.
1860 w 1700 vw 1600 vw 1060 sh 1038 m 2010 sh 1955 m 1845 m Ethanol
1112 s(liq), 1057 s(gas) 1030 s
by G. Blyholder’ and Laurence D. Neff
1089 s 1050 s 880 s 802 w 657 s 433 m
In order to examine the validity of using an analogy between coordination complexes and heterogeneous reactions on metals, we are examining the structure and reactions of surface species on Co surfaces and comparing them to similar reactions of Co complexes. In order for the comparisons to be meaningful the structure of surface species must be det’ermined. Whereas the structures of a vast number of coordination complexes are well known, relatively little is known about the structural details of species adsorbed on metal surfaces. The interaction of alcohols and aldehydes with Fe2 and Nia which are adjacent to Co in the periodic table produce quite different surface species. Thus the surface species produced on Co are important in further defining the role of the number of “d” electrons in determining the structure of surface species. The surface species on cobalt are also important for the understanding of the oxo or hydroformylation reaction which has received much attention.4 In a previous study the infrared spectra of alcohols adsorbed on silica-supported Co has been reported.6 Because the silica support permits only the C-H and C=O stretching regions to be examined, the assignment of the principal bands to an alkoxide structure cannot be considered to be firmly based except in the one case of a methoxide. A wide spectral range experimental technique, which has been described in detail elsewhere6 was used here. It consists of evaporating Co from an electrically heated tungsten filament in the presence of a small T h e Journal of Physical Chemistry
2010 m 1950 m 1850 m Ethylene oxide
Acyl CO str CHa rock Skeletal str Skeletal str CHz O’H bend M-0 str Skeletal bend Added CO Added CO Added CO
Ethanol 1995 vw 1088 w 1030 w 885 w
Acetaldehyde 1150 vw 1090 w 1040 w 885 w a
CO stJr. Added CO Added CO Added CO Chemisorbed CO Acyl CO str
483 vw
Department of Chemistry, University of Arkansas, Fayetteville, Arkansas 73701 (Received March 15, 1069)
Chemisorbed CO Acyl CO str Acyl CO str CH3 rock
Ethanol5 1890 vw 1700-1750 vw 1600 vw 1093 m 1047 m 890 m
Structure of Surface Species on Cobalt
Assignments
Methanol“
Methanol
-
cm-l---Model compounds
1149 w 1089 s 1050 s 880 s 802 w 657 s 433 m Ethanol 1149 w 1089 s 1050 s 880 s
Chemisorbed CO CHI rock CHa rock Skeletal str Skeletal str CH2 OH bend Skeletal bend CH3 rock CH3 rock Skeletal str Skeletal str
Reference 7.
pressure of helium. The metal particles formed in the gas phase deposit in a purified hydrocarbon oil film on the salt windows of an infrared cell. The gas to be studied is then admitted to the cell and the spectrum of the chemisorbed species obtained. Spectra are recorded before and after admission of the gas to the cell. (1) Address inquiries to this author at the University of Arkansas. (2) 6. Blyholder and L. D. Neff, J . Phys. Chem., 70, 893 (1966). (3) G.Blyholder and L. D. Neff, {bid.,70,1738 (1966). (4) R.F.Heck and D. S. Breslow, “Actes du Deuxieme International de Catalyse,” Editions Technip, Paris, 1961,p 671. (5) G.Blyholder and W. V. Wyatt, J . Phys. Chem., 70, 1745 (1966). (6) G.Blyholder, J . Chem. Phys., 36,2036 (1962). (7) C.Tanaka, N i p p o n Kagaku Zasshi, 83,792 (1962).
