The Molecular Structure of Nitrogen Dioxide. a Reinvestigation by Electron Diffraction Stig Claesson, Jerry Donohue, and Verner Schomaker

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The Molecular Structure of Nitrogen Dioxide. A Reinvestigation by Electron Diffraction Stig Claesson, Jerry Donohue, and Verner Schomaker

Citation: The Journal of Chemical Physics 16, 207 (1948); doi: 10.1063/1.1746836 View online: http://dx.doi.org/10.1063/1.1746836 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/16/3?ver=pdfcov Published by the AIP Publishing

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Reuse of AIP Publishing content is subject to the terms: https://publishing.aip.org/authors/rights-and-permissions. Downloaded to IP: 131.215.225.186 On: Mon, 17 Oct 2016 20:13:28 STRUCTURE OF NITROGEN DIOXIDE 207

percent of the total binding energy, it should be ACKNOWLEDGMENT noted that the resonance energy is a very sensi The authors wish to express their appreciation tive function of inter-iodine distance in this to Professors Henry Eyring and Walter Kauz region so that a slight error in calculation may mann for discussions which have been of help in materially change the resonance contribution. the preparation of this paper.

THE JOURNAL OF CHEMICAL PHYSICS VOLUME 16, NUMBER 3 MARCH, 1948

The Molecular Structure of Nitrogen Dioxide. A Reinvestigation by Electron Diffraction *

STIG CLAESSON, JERRY DONOHUE, AND VERNER SCHOMAKER Department of Chemistry, California Institute of Technology, Pasadena, California (Received November 18, 1947)

An investigation of the structure of the nitrogen dioxide molecule has been made by the electron diffraction method. The interpretation of the photographs, which showed rings extend ing to values of q of nearly 100(q=40/A sin.J/2), leads to the following structural parameter values: N-O=1.20±O,02A,

INTRODUCTION equilibrium measurements5 on the dissociation N recent years the molecular structure of nitro of nitrogen dioxide in connection with spectro I gen dioxide has been the subject of numerous scopic data for nitric oxide,6 oxygen,7 and nitro 8 investigations but, aside from general agreement gen dioxide rule out the suggestion of Zeise that on a non-linear symmetrical structure with a the molecule has a multiplicity of 4. This sug wide bond angle and a multiplicity corresponding gestion is likewise ruled out by the results of the magnetic susceptibility measurements of to only the odd electron, the conclusions have Havens,9 as was pointed out by Harris and been surprisingly divergent. This is true of the King.lo dielectric constant measurements on the N02 From consideration of an assumed electronic - N 20 system, which have lead variously to the 4 structure Paulingll predicted 1.18A for the ni conclusions that both nitrogen dioxide and nitro trogen-oxygen distance and 1400 for the angle gen tetroxide have small constant dipole mo O-N -0. On the assumption of a valence po ments of the order of 0.4 X 10-18 e.s. u., that of tential function and a frequency assignment sug nitrogen tetroxide being the greater,I,2 and that gested by the infrared spectrum Penney and nitrogen dioxide has a moment of this magnitude Sutherlandl2 obtained the value 1140 for the bond which decreases with increasing temperature angle. With a similar assumption but a slightly while nitrogen tetroxide has a zero moment.3 It is especially true of the bond angle and bond 5 Especially those of M. Bodenstein and Lindner, Zeits. distance estimates and determinations, which f. physik. Chemie 100, 82 (1922). naturally concern us directly. However, Giauque 6 H. L. Johnston and A. T. Chapman, J. Am. Chern. Soc. 55, 153 (1933). and Kemp's4 comprehensive considerations of the 7 H. L. Johnston and M. K. Walker, J. Am. Chern. Soc., 55, 172 (1933). 8 H. W. Zeise, Zeits. f. Elektrochemie 42, 785 (1936). * Contribution from the Gates and Crellin Laboratories 9 G. G. Havens, Phys. Rev. 41, 337 (1932). of Chemistry, California Institute of Technology, No. 1156. 10 L. Harris and G. W. King, J. Chern. Phys. 8, 775 1 C. T. Zahn, Physik. Zeits. 34, 461 (1933). (1940). 2 R. W. Schultz, Zeits. f. Physik 109, 517 (1938). 11 L. Pauling, The Nature of the Chemical Bond (Cornell 3 J. W. Williams, G. H. Schwingel, and C. H. Winning, University Press, Ithaca, New York, 1940), second edition, J. Am. Chern. Soc. 58, 197 (1936). p.270. 4W. F. Giauque and J. D. Kemp, J. Chern. Phys. 6, 40 12 W. Penney and G. B. B. M. Sutherland, Proc. Roy. (1938). Soc. A156, 654 (1936).

1.25

..: ,; C.i ~" :6 1.20 0 I I I Z 2 6 •I A 1.15 B A

c 1.10 '--__--' ___ --L ___ ..J- ___'-- __~

110°

13 G. W. Herzberg, Infrared and Raman SPectra (D. Van 17 In calculating the changes in the values of the thermo Nostrand Company, Inc., New York, New York, 1945), dynamic quantities (FO - HoO)/T of nitric oxide and oxygen p.170. it was assumed that whatever change in these values would 14 L. R. Maxwell, V. Mosley, and L. Deming, ]. Chern. result from changing the constants is identical with the Phys. 2, 331 (1934). ' change in the calculated result for a rigid rotator harmonic 16 L. R. Maxwell and V. Mosley, ]. Chern. Phys. 8, 738 oscillator approximation, plus a 120 cm-1 doubling of all (1940). levels of nitric oxide, since the original calculations (see 16 R. Spurr, quoted in Yost and Russell, Systematic references 7 and 8) made use of the spectroscopically ob Inorganic Chemistry (Prentice-Hall, New York, New York, served levels and a recalculation on that basis would be 1944), p. 27. somewhat complicated.

= 1.50 X to-116 g3 cm 6 is probably known to nitrogen dioxide was complete before the gas about 5 percent. entered the diffraction chamber. We have reinvestigated the structure of nitro The photographs were examined on a viewing gen dioxide by the electron diffraction method; box equipped with a lamp of adjustable intensity, we find 1.20±0.02A for the nitrogen-oxygen dis and, for the outer rings, two or more good photo tance and 132±3° for the bond angle. This result graphs were superimposed. Measurements of the together with the various results mentioned diffraction features were made in the usual way. above are shown in Fig. 1. Because of the simplicity of the problem the customary radial distribution treatment was EXPERIMENTAL omitted and only the correlation methodI9 Nitrogen dioxide was prepared by heating lead was used in interpreting the photographs. The nitrate in a stream of oxygen. The gas was con formula densed with dry ice and then twice distilled in an ZiZj atmosphere of oxygen in an all-glass apparatus. I(q) = L --sin (7r-rijq ) Electron diffraction photographs were taken ii r ij to with the apparatus described by Brockway.I8 An all-glass high-temperature nozzle of special de was used to calculate simplified theoretical in sign shown in Fig. 2, was used to heat the gas tensity curves, shown in Fig. 3, for six models sample before the photographs were taken. The with N -0=1.20A and LO-N -0=125°,130°, length of the chimney, which was heated to 140° 132!0, 135°, 140°, and 145° respectively. These before each exposure, was sufficient to insure calculations were made on International Business that the dissociation of nitrogen tetroxide to Machines with punched cards.20

125'

130' FIG. 3. Electron diffraction curves for nitrogen dioxide. Ni trogen-oxygen distance 1.20 A for all models, O-N -0 angles as 132f indicated. The three sets of lines with the curve for the 132!O model represent the measure ments of the three observers: 135' those below the curve: S. c.; on the curve: V. S.; above the curve: J. D. 140'

145'

o 20 40 60 80 100 q

18 L. O. Brockway, Rev. Mod. Phys. 6, 234 (1936). Wave length calibration: C. S. Lu and E. W. Malmberg, Rev. Sci. Inst. 14, 2181 (1937). The lattice constants of zinc oxide given by them in kX units were converted to ang strom units. 19 L. Pauling and L. O. Brockway, J. Chern. Phys. 2, 867 (1934). 20 P. A. Schaffer, Jr., V. Schomaker, and L. Pauling, J. Chern. Phys. 14,659 (1946).

TABLE I. Results of measurements of electron diffraction a convincing minimum in the average deviations photographs of nitrogen dioxide. very near 132°, substantiating the value of the Number of bond angle determined by the correlation treat Average value of Average features included Observer Q13"'/Qob •. deviation in average ment. Measurements on the extreme inner and S. C. 0.996 0.006 6 outer features, indicated by dotted lines in Fig. 3, J. D. 0.999 0.004 7 were considered by the respective observers to 0.999 0.008 12 V. S. 1.003 0.007 7 be unreliable, and were not included in any 1.002 0.008 16 averages. The averaged results of the three ob servers give for the nitrogen-oxygen distance 1.20A. In consideration of the average deviations RESULTS shown in Table I and the uncertainty in the bond As may be seen in Fig. 3, the character of distance arising from the uncertainty in the bond the features of the theoretical intensity curves angle obtained by the correlation treatment, we changes rapidly with change in bond angle. Com estimate the limit of error of the nitrogen-oxygen parison of these curves with the appearance of distance to be ±0.02A. the photographs fixes the bond angle at 132±3°. The features at q:::55, 70, and 85 were particu DISCUSSION larly useful in fixing the bond angle. The relative Our results are in fairly good agreement with the heights of the components which comprise these previous electron diffraction results of Maxwell three doublet maxima are in best agreement with and Mosley;15 we feel that ours are somewhat the appearance of the photographs at 132°. At more accurate because we observed features at larger bond angles the outer components of the larger q values than did the previous investi rings at q"'70 and 85 are too strong; at smaller gators. Moreover, our results are in better agree bond angles the ip.ner components of the rings at ment with the product of the moments of inertia. q:::55 and 70 are too strong, and the outer com It is apparent that the structures derived from ponent of the ring at q:::85 disappears. the spectroscopic considera tions10.12. 13 are con Between seven and twenty-five measurements siderably in error. were made on each of the features measured by The structure found for the nitrogen dioxide the three observers. The average values of q132° molecule is in good qualitative agreement with (obtained by interpolation) divided by qob •• are the discussion of Pauling,ll who predicted a bond presented in Table I. We consider those obtained distance slightly larger than that of a nitrogen from the measurements indicated by the solid oxygen double bond, and a bond angle inter lines in Fig. 3 to be the most reliable. The aver mediate between 125°16', the double bond value, ages obtained from these measurements together and 180°, corresponding to the following resonat with those indicated by the dashed lines in Fig. 3 ing structure for the molecule: include features which are more difficult to meas ure; it is interesting that the average values of O' '0 q132°/qobs. are not changed appreciably by includ "~ /., ing these measurements. The averages q/qobl. and N the average deviations were calculated for the ACKNOWLEDGMENT measurements of the smaller sets of features of each of the three observers for the 125°, 130°, We wish to thank Mr. Kenneth Hedberg for 135°, and 140° models also. In each case there is his assistance in preparing the photographs.

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