3677
NOTES
2
4
3
5 €'
the Cole-Cole plot' and the plot of loss factor us. frequency are obtained and are shown in Figures l a and b, respectively. The Cole-Cole plot yields a semicircle with the extrapolated infinite frequency dielectric constant em = 2.18 and the relaxation time 7 = 5.4 X 10-12 sec. These values are in good agreement with e, = 2.16 8 at 20" and 7 = 5.4 X 10-l2 sec at 30" reported in the literature. Antony and Smyth,l0however, report the same value for 7 at 20". The values of e, calculated from the experimental values of e' and e'' at different wavelengths agree with each other within the limit of experimental error. It is also seen that the loss factor-frequency curve shows only one peak, and the data on the low frequency side of the peak seem to be consistent with the data of Conner and Symth2 rather than that of F i ~ c h e r . ~Using the value of e,, PE+A, the sum of the electronic and atomic polarization, = (em - 1)M/ was calculated from the relation PE+A (e, 2)d, where M is the molecular weight and d is the density. The value of PE+Athus obtained was 22.79 cc. PE,the electronic polarization, was calculated to be 20.79 cc by using the Cauchy dispersion equation" PE = R[1 - (ho2/h2)]
+
I
1
5
IO
.
>
20
I
....
50 10
W X IO
IN
RADIANS
I
I
100
ZOO
SEC.-'
Figure 1. (a) Cole-Cole plot for chloroform a t 30'; (b) loss factor E'' us. angular frequency w for chloroform a t 30'. The points marked by X indicate the 2.2-mm measurement a t 20' of S. K. Garg and C. P. Smyth, J. Chem. Phys., 42, 1397 (1965).
method involves the free-space analog of a shorted-line reflectometer. Electromagnetic energy at 3.05 mm was produced using a harmonic doubler and the 6.1-mm klystron source. The 1.2-mm measurement was made using a FS-520 Fourier spectrophotometer, manufactured by the Research Industrial Instrument Company, London. The accuracy in the determination of e' was 1% and in the determination of e'' was 3%, The static dielectric constants have been measured at a frequency of 50 kc using a 716-C General Radio capacitance bridge. The accuracy in the determination of the static constants was 0.5%. The refractive indices have been measured using an Abbe refractometer. The calculations of the dielectric constant and loss factor were made using an IBM 360 computer.
where R is the refraction at wavelength X and Xo is the characteristic wavelength. The value of PA,the atomic polarization, thus obtained was 2.01 cc. This value is slightly higher than the 1.57 cc12found in the literature.8 The present value, however, is low compared with the value of 4 cc obtained from the variation of the total polarization with temperature in the gaseous state.'* The value from gas measurements is uncertain, however, because of long extrapolation.
Acknowledgment. We express our thanks to Miss Lena Foley for typing the manuscript. (7) K. 8. Cole and R. H. Cole, J. Chem. Phys., 9, 341 (1941). (8) 5.X. Garg and C. P. Smyth, ibid., 42, 1397 (1965). (9) S. Mallikurjun and N. E. Hill, Trans. Faraday Soc., 16, 1389 (1965). (IO) A. A. Antony and C. P. Smyth, J. Amer. Chem. Soc., 86, 152 (1964). (11) C. P. Smyth, "Dielectric Behavior and Structure," MoGrawHill Book Co., Inc., New York, N. Y.,1955, p 405. (12) This value is erroneously reported as 1.77 in ref 8. (13) Reference 11, p 420.
Materials Chloroform was obtained from the Eastman Kodak Co. and was chromatoquality reagent grade.
Electron Affinities and the Electron-Capture Method for Aromatic Hydrocarbons
Results and Discussion The dielectric constant and loss of chloroform have been measured at 10.09, 3.21, 2.68, 2.17, and 1.29 cm and 6.1, 3.05, and 1.2 mm at 30". The measured static dielectric constant at 30" was 4.65 and the measured refractive index was 1.4454. Using these data,
by L. E. Lyons, G. C. Morris, and L. J. Warren Department of Chemistry, University of Queensland, Brisbane, Australia (Received April 22, 1968)
The electron-capture method' of Wentworth, Chen, and Lovelock yields an energy quantity, which we call Volume 73,Numbw 10 October 1068
3678 4.2
4.0
NOTES
1
When E is plotted against relative values4 of Asoln, our values of E do not fall on the Chaudhuri, et al., 45" line: their conclusion (that the difference between the free energy of solvation of an aromatic anion and that of the neutral molecule is constant over a range of hydrocarbons) therefore is not yet confirmed.
3.8 .
5
2
3.6
5z 3.4 3.2
3.0 2.8
1 '
t
1 2.0
2.1
2.2
2.3
2.4
2.5
10a/T.
Figure 1. Plots used to determine values of E ( I , current when an electron-capturing species is present in the capture chamber; A I , drop in current when an electron-capturing species enters the capture chamber): A, anthracene (linear in the range 182-210'); B, pyrene (linear in range 172-207'); C, naphthacene (linear in the range 152-170'). Of the five recorded curves for each substance only a typical curve is shown. The experimental conditions were similar to those in ref 2.
E . Wentworth, et al., have identified E with the molecular electron affinity, A,. A modified procedure2 has been used t o find further values of E for two key hydrocarbons and to test a predicted value for naphthacene. Average results (Figure 1) are: anthracene, 0.57 f 0.02 eV; pyrene, 0.50 f 0.03 eV; naphthacene, 0.88 =t 0.04 eV. These are "determined-intercept" results;a ie., they have been obtained from the slopes of the lines in Figure 1. The anthracene result agrees with Becker and Chen's3 but differs from the prediction of 0.74 eT7 by Chaudhuri, et al.4 The pyrene result is lower than Becker and Chen's by 0.07 eV, but our value is supported by the fact that we found E for anthracene was greater than E for pyrene by 0.07 eV, in agreement with the average difference of Asoln (affinity in solution) (0.09 f 0.04 eV)4-6 and that of A, (affinity in the gas) calculated theoretically (0.06 eV) E for naphthacene is lower than the predicted4 value 1.15 eV for A,. Relative to anthracene our value of E for naphthacene is that expected from the difference in A values for the two molecules (0.38 f 0.04 eV).4-6p8 This suggests that the electron-capture technique may yield E values higher than previously t h ~ u g h t . ~ If E values are identifiable with A , values, then the molecular electronegativity x = O.5(Ag I ) , where I is the ionization potential from photoionization,6,10,11 varies from 3.98 f 0.03 for anthracene t o 3.88 f 0.04 for naphthacene. A similar drift in molecular electronegativity follows also from Figures 1 and 2 of ref 3, where the plots of (i) I us. absorption maxima (hv) and (ii) A , us. hv have slopes differingby about 50%. The experimental results so far obtained do not support a constant x value for this series of molecules.
.'
+
The Journal of Physical Chemistry
Acknowledgment. This research was sponsored by the U. S. Air Force Office of Scientific Research, Office of Aerospace Research, Directorate of Chemical Sciences, under Grant KO. AF-AFOSR-863-65 and by the Australian Research Grants Committee. We thank the Commonwealth Scientific & Industrial Research organization (CSIRO) for a scholarship to 1,. J.
w.
(1) W. E. Wentworth, E. Chen, and J. E. Lovelock, J . Phys. Chem., 70,445 (1966). (2) L. E. Lyons, G. C. Morris, and L. J. Warren, Aust. J . Chem., 21, 853 (1968). (3) R. S. Becker and E. Chen, J . Chem. Phys., 45, 2403 (1966). (4) J. Chaudhuri, J. Jagur-Grodzinski, and M. Szwarc, J . Phys. Chem., 71, 3063 (1967). ( 5 ) I. Bergman, Trans. Faraday Soc., 50, 829 (1954). (6) M. Batley, Ph.D. Thesis, University of Sydney, 1967. (7) J. R. Hoyland and L. Goodman, J . Chem. Phys., 36,21 (1962). (8) M. A. Slifkin, Nature, 200, 877 (1963). (9) R. S. Becker and W. E. Wentworth, ibid., 203, 1268 (1964). (10) A. Terenin and S. Vilesov, Advan. Photochem., 2 (1964). (11) F. I. Vilesov, Dokl. Akad. Nauk SSSR, 132, 632 (1960).
Inhibition by
C302
of the Explosive
Combustion of CO by Jean Lebel, Pierre Michaud, and Cyrias Ouellet Dkpartment de Chimie, Universitd Laval, Qudbec, Canada (Received April SO, 1968)
I n the course of an investigation of the combustion of ( 2 3 0 2 above 560°, we have observed delayed explosions following accumulation of CO and COz in the system. These explosions took place only after C302 had been consumed, indicating that this compound inhibits the explosive combustion of CO. The possibility of such an inhibition has already been suggested by Harteck and Dondesl in connection with the slow combustion of CO. We therefore studied the explosive combustion of CO in the presence of added GO2, and we also tried t o detect the formation of this compound during the slow combustion of CO-rich mixtures. Carbon suboxide was prepared by dehydration of malonic acid following the technique of Long, Murfin, and Williams2 in the version described by Batchelor, (1) P. Harteck and S. Dondes, J . Chem. Phys., 27, 1419 (1957). (2) D. A. Long, F. S. Murfin, and R. S. Williams, Proe. Roy. Soc., A223, 251 (1954).
