J, Phys. Chem. 1980, 84, 2083-2084
geometric standard deviations of the accumulation mode. Consequently D 1, and, as the mean free path in the final impactor stage is about 0.25 pm, it holds for the particles of the nucleation mode. Moreover as 2.5Xg/D = 6.9 is fairly large in comparison to unity the slip correction factor may be further reduced to C = 2.5Xg/D. In this approximatioii eq 1 becomes
+
D, = Do(Po/Pp)
(5)
which has already been used earlier in this paper. The diameter conversion factor is independent of particle size, and consequently the diameters are shifted, but the standard deviations are not inflicted under this conversion.
2083
In summary, the modal diameters are shifted to smaller values under the diameter conversion, however, the standard deviations can be transferred without change. Assuming densities of 2.6 g/cm3 for the coarse mode particles and 1.8 g/cm3 for the accumulation mode particles, we find almost complete correspondence between the impactor data and data reported by Whitby.l Coarse Mode: The diameters were as,,follows: average, 7.4 pm, 8.1 pm; exceptional, 17.4 pm, 23.6 pm; average range, 6.8-8.4 pm; Whitby’s range, 5-30 pm. The geometric standard deviations were average, 2.8, 2.9, 3.2; average range, 2.3-3.8; Whitby’s range, 2-3. Accumulation Mode: The diameters were as follows: average, 0.43 pm, 0.44 pm; exceptional, 0.71 pm; average range, 0.37-0.46 pm; Whitby’s range, 0.15-0.5 pm. The geometric standard deviations were as follows: average, 1.68, 1.8, 1.79; average range, 1.4-2.2; Whitby’s range, 1.6-2.2.
References and Notes Whitby, K. T. Atmos. Environ. 1978, 72, 135-159. Friedlander, S.K. Atmos. Environ. 1978, 72, 187-195. Chuan, R. L. “Rapid Measurementsof Particulate Size Distribution”, in “Find Particles”; Liu, 8. Y. H., Ed.; Academic Press: New York, 1976. Berner, A.; Lurzer, Ch.; Pohl, F.; Preining, 0.;Wagner, P. Scl. Total Environ. I n press. Berner, A. In “Aerosol Measurementsin the Submicron Sire Range”; EPA-600/2-79-105; Washington, D.C., 1979. Lurrer, Ch. “Messung trimodaler Massengrossenvertellungenurbanen Aerosols mit Kaskadenlmpaktoren”, GAF-Konferenz 7, 1979. Puxbaum, H. Z. Anal. Cbem. In press. Puxbaum, H. Z. Anal. Cbem. In press. Lurzer, Ch.; Berner, A. J. Aerosol. Scl. 1979, 70, 231. Berner, A. Chem. Ing. Tech. 1978, 50, 399. Berner, A. ”Praktlsche Erfahrungen mA einem 20-Stufen-Impaktor”; Stabu-Reinh. Luft 32, 1972; p 315. Berner, A. “Dle Messung der Verteilungsfunktion von Stiiuben mHtels vielstufiger Kaskadenlmpaktoren”, EGKS-Report, 1970. Cohen, J. J. Am. Ind. Hyg. Assoc. J . 1967, 28, 95. Strasser, J. J. Aerosol. Sci. 1079, 10, 236.
COMMUNICATIONS TO THE EDITOR Comment on “Adsorption of Alcohols on Alumina. 1. Gravimetric and Infrared Spectroscopic Investigation”
Sir: Infrared studies of the adsorption of alcohols on alumina have shown that at least two types of chemisorbed species occur: alkoxide species, resulting from a dissociative chemisorption, and carboxylate species, formed at higher temperatures. Knozinger et a1.l consider that a third species may alelobe formed by coordinative chemisorption onto Lewis acid sites. This could be a precursor of dissociative adsorption. In a recent paper, Knozinger and Stubner2reported infrared results on the adsorption of isobutyl alcohol on1 v-A1203from which they concluded that an alcohol molecule is indeed coordinated to an anion vacancy. This result was mainly deduced from the study of (CH3)2CHCD20Hadsorption; the adsorption shifts the v(CD2)vibrations toward lower frequencies, which is taken as evidence for the formation of the postulated coordinated species. We here report some results which rather indicate that the CH stretching frequencies increase when ethers 0022-3654/80/2084-2083$0 1 .OO/O
or alcohols are coordinated and decrease when dissociative adsorption of alcohols occurs. The observation of CH stretching frequencies of CHDz groups, first carried out by Saur, Lavalley, and Romanet in CH3CH2Xcompounds,3 has demonstrated that the CH bond in the plane of dimethyl ether is slightly stronger than the out-of-plane bonds.4 The low frequency associated with the latter has been explained by a participation of the lone pair to a a* CH orbital on the adjacent carbon atom.5 This effect has been evidenced through the disappearance of the weak bond frequencies when the lone pairs were involved in complex formation, such as (CH&0-A1Cl3 or (CH3)20-BF3.6 Figure 1 illustrates how coordination of CD30CD2Hwith A1C13 affects the v(CH) vibrations of the ether; the two v(CH) frequencies increase, whatever the position of the CH bond. This is in agreement with Derouault’s results obtained by force constant refinement of (CH3)20-AlX3complexes.’ Correspondingly, Yakerson et a1.8 noticed an increase of v(CH) frequencies when CH30CH3coordinates onto alumina. We confirm this result using CD30CD2H(Figure 1); admission of 40 0 1980 American Chemical Society
2084
J. Pbys. Cbem. 1980, 8 4 , 2084-2085
HCECCH~OHand CX3CH20Has evidenced by a study of coupling between 6(OH) and bending CH2vibrations." References and Notes I
2886
.
H
D
(1) H. Jeziorowski, H. Knozinger, W. Meye, and H. D. Muller, J . Cbem. Soc., Faraday Trans. 1 , 69, 1744 (1973). (2) H. Knozinger and B. Stubner, J . Pbys. Chem., 82, 1526 (1978). (3) J. C. Lavalley, ThBse, Caen, 1969; 0. Saur, J. C. Lavalley, and R. Romanet, C . R . Acad. Sci. Paris, Ser. B , 269, 816 (1969). (4) A. Allan, D. C. McKean, J. P. Perchard, and M. L. Josh, Spectrochim. Acta, Part A , 27, 1409 (1971). (5) H. P. Hamlow, S. Okuda, and N. Nakagawa, Tetrahedron Lett., 37, 2553 (1964). (6) E. Taillandier, Thbse, Park, 1970: J. Derouault, J. Le Calve, and M. T. Forel, Spectrocblm. Acta, Part A , 28, 359 (1972). (7) J. Derouault, Thbse, Bordeaux, 1971. (8) V. I. Yakerson, L. I. Lafer, V. Ya. Danyushevskll, and A. M. Rublnshteln, Izv. Akad. Nauk SSSR, Kbim., 10, 2246 (1967). (9) J. C. Lavalley and J. Caillod, J . Cbim. fbys., 77, 373 (1980). (10) J. Derouault, T. Driembowska, and M. T. Forel, J. Mol. Struct., 47, 59 (1978); Spectrocbim. Acta, Part A , 35, 773 (1979). (11) J. Travert, J. C. Lavalley and 0. Saur, to be submmed for publication. (12) J. Travert, 0. Saur, A. Janin, and J. C. Lavalley, J. Mol. Struct., 33, 265 (1976).
D
2956
Flgure 1. IR spectra of CD30CDJ,i (2800-3100-~m-~ range) (a)in CCI, solution, (b) coordinated to AICI, (L = AICI,), and (c) chemisorbed on y-alumina activated at 870 K.
Professor Knozinger agrees with this comment. ERA 824 Structure et Mactivh5 des Esp6ces Adsorbees Laboratoire de Spectrocbimie I.S.M.R.A., Universit6 de Caen 14032 Caen Cedex, France
TABLE I: v(CH) Wavenumbers of Some Alcohols and Their Corresponding Alkoxide Species Formed on r-Al,O, CD,HOH CD,CDHOH CC1,CDHOH
In CCI,, ref 12.
alcohola
alkoxide
-2965 sh 2920 -2940 sh 2898 2964 2921
2960b 2930b -2925 shc 288!jC 2965' 2900'
Reference 9.
Received: October 18, 1979
' Reference 11.
pmol g-l of CD30CD2Honto y-A1203produces a band pair at 3015 (very weak) and 2956 cm-' (with a shoulder on the high-frequency flank). The most relevant feature is the strong shift of u(CH) modes which allows us to use CD3OCD2H as a very suitable probe molecule to study the Lewis acidity of catalytic oxide surface^.^ Similarity between spectra of CD30CD2H coordinated to AlC13 and adsorbed onto A1203 (Figure 1) clearly shows that coordinative adsorption occurs on alumina. Alcohols. Recently, Derouault et al.,'O studying CH30H complexation with BF3, showed that the CH stretching modes are also observed at wavenumbers greater than those of free methanol. On the other hand, we have found that adsorbed v(CH) wavenumbers of alkoxide species formed when alcohols are adsorbed onto y-alumina generally shifted to lower values as compared with those of the corresponding alcohol in CC1, solution (Table I). Note that use of undeuterated alcohols does not lead to such clear shifts owing to the fact that 4CH) fundamentals are in Fermi resonance with 26(CH2)and 2w(CH2)overtones." By analogy with the present results on u(CH) vibrations of ethers and alcohols, one would conclude that the reduction of v(CD2) frequencies of (CH3)&HCD20H adsorbed onto alumina2points to a dissociative chemisorption of isobutyl alcohol rather than a coordinative adsorption. However, the possibility of coordinative chemisorption is not ruled out as a precursor state. In fact, it is difficult to predict u(CH) vibrations of species like R\
Jean-Claude Lavalley Jack Calllod Joseiie Traveri
0 .' ,H
I 0:
AI
as both effects (coordination and dissociation) affect u(CH) vibrations of the RO group in opposite directions. Note that fully dissociated species are observed in the case of This article not subject to U S . Copyright.
Irreversible Reaction of Nltromethane at Elevated Pressure and Temperature
Sir: Nitromethane was chosen as a model compound for a study of the effects on secondary explosives of high pressures and high temperatures similar to those in shock waves. A reaction has been observed when nitromethane is subjected to pressures of 50 kbar and temperatures of 150 "C. The product is dark in color and ranges from a viscous liquid to a powdery solid depending on reaction conditions. The reaction is completely irreversible; the product is thermally stable, persists at ambient conditions for at least several weeks, and appears to be insoluble in common organic solvents, water, and dilute acids. Figure 1illustrates a typical infrared spectrum of the final product at ambient conditions compared to the spectrum of nitromethane. Although infrared spectra of the product indicate a very simple molecular structure, a satisfactory identification has not been made. Attempts to obtain corroborating information by mass spectrometry and Raman spectroscopy have been unsuccessful to date. The primary impediment in identification is the minute amount (
