COMMUNICATIONS TO THE EDITOR
2372
C2H&1+
Table I :
Product Distribution from the Reaction of Di-t-butyl Peroxide with Ethyl Chloride Run
TemDerature Reaction time C2H6C1,initial pressure Di-t-BP, initial pressure Products
CHaCl HCl
no. 1
Run no. 2
189°C 8 min 45.4 mm 23.6 mm
163°C 25 min 38.3 mm 15.7 mm
20.2 mm 1.Omm 2.9 mm 1.Omm Trace
11.7 mm 0 . 5 mm 2 . 1 mm 0 . 5 mm Trace
a
a
C3H7
+ HC1-
CzH,
+ C1 (7)
C3Hs
+ C1
(8)
The nature of the products with other alkyl chlorides and bromides indicated comdicated reaction svstems of a similar nature. These studies have therefore been discontinued because of the difficulty in obtaining useful quantitative information from such complicated systems.
Not measured quantitatively. Its presence was tested for by a procedure similar to that used by Hogg and Kebarle.6
SCHOOL OF CHEMISTRY THEUNIVERSITY OF NEW SOUTH WALES SYDNEY, AUSTRALIA
K. D. KING E. S. SWINBOURNE
RECEIVED MARCH 27. 1967
di-&butyl peroxide was increased (see Table 11). However, we feel that in our experiments the ethylene is also produced from decomposing chloroethyl radicals C2HdCl+
C2H4
+ C1
Comment on “Electron Spin Resonance of
01W17, 017-018, and 018-016” by L. K. Keys
Correspondinglyl propene was probably via bromopropyl radicals with similar experiments using n-propyl bromide.
Sir; We wish to call in question number of statements in s, recent communication by on the electron resonance spectrum of gaseous 02. First, it is not the case that lines below 5500 gauss
~~
Table 11: Effect of Ethyl Chloride Concentration upon the
Relative Production of Ethylene and Ethane at 163” [(CxHsCl)/ (Di-t-RP)1initial
0.4 1.6 2.4
Isobutylene oxide is one of the major products resulting from chlorine atom attack on di-l-butyl peroxide,6 but was not detected among our products. Conditions in our experiments probably favored chlorine atom attack upon the hydrogen atoms in the alkyl halides in preference to those on the di-&butyl peroxide. The fully halogenated compounds used in the experiments of Tomkinson and Pritchard2 would be inert to chlorine atom attack. Likely reactions resulting from methyl radical attack on ethyl chIoride are
+ CzH&l----f CH4 + CZH4C1 CH3 + c~HsC1 CHaC1 + C2H6 CHs + CH3 +C2He CH3
The Journal of Physical Chmiatry
(1) (2)
(3)
(at X-band frequency) have not previously been reported. Tinkham and Strandberg,2 in their classic papers on 0 2 , list no fewer than 35 lines between 1400 and 5500 gauss and interpret all of them with high accuracy in terms of 0l6-Ol6 alone. Second, the formula E = g j/3HMj is quite inapplicable to the 0 2 molecule, for a number of reasons. Even if there were no zero-field splitting of the spin triplet, this formula would be inadequate because of off -diagonal magnetic field matrix elements which give rise t o a nonlinear Zeeman effect. However, as shown originally by K r a m e r ~ ,and ~ in more detail by Van Vleck4 and by Tinkham and Strandberg, the spinspin and spin-orbit interactions are extremely important. They split the triplet components of each rotational level, the J = N & 1 components being separated from the J = N component by about 2 cm-l. The J = N f 1 components are themselves not degenerate and the splitting between them to l cm-’ for different rotational levels) is sufficient for the (1) L. K. Keys, J . P h y s . Chem., 70,3760 (1966). (2) M. Tinkham and M. W. P. Strandberg, Phys. 951 (1955). (3) H. A. Kramers, Z . Physik, 53,422,429 (1929). (4) J. H. VanVleck, Phys. Rev., 71,413 (1947).
Rev.,97,
937,
COMMUNICATIONS TO THE EDITOR
2373
AJ = k 2 transitions, which are allowed in a magnetic field, to occur at considerably less than 5500 gauss a t X-band frequencies. These are the lines observed by Keys. The suggestion by Keys that some of the lines below 5500 gauss arise from the isotopic species 016-0”and 0 1 7 - 0 1 * deserves comment on other grounds. The natural abundance of 0 17-018 is approximately 0.016%. Taking into account the sixfold hyperfine splitting from 0 1 7 (i.e., 21 1, not 2S(S 1) as given by Keys), lines implies a signal-to-noise observation of 0 17-01* ratio of approximately lo6 to 1 for some of the 0l6-Ol6 lines. On the basis of our experience with a Varian 100-kc epr spectrometer, Keys’ hopes of 017-018 resonances, even a t 77”K, are about three orders of magnitude too optimistic.
+
+
DEPARTMENT OF THEORETIC.4L UNIVERSITY OF CAMBRIDGE ENGLAND CAMBRIDGE,
CHEMISTRY
A.
CARRINGTON
D. H. LEVY T. A. MILLER
ACCEPTED ANI) TRANSMITTED BY THEFARADAY SOCIETY
DECEMBER 22, 1966
there are still discrepancies in the various theories to explain the absorption peaks. In view of the recent observation of the hfs of 0 1 7 in SiOJ7and the high spin molecular density of oxygen, it is believed that 0 1 7 can contribute to the observed esr spectra of oxygen. The reported possible 01“017 transitions would be naturally very weak and are believed only to contribute possibly to the background esr of oxygen. (1) L. K. Keys, J . Phys. Chem., 70,3760 (1966). (2) A. F.Henry, Phys. Rev., 80,396 (1950). (3) M. Tinkham and M. W. P. Strandberg, ibid., 97, 937, 951 (1955). (4) A Carrington, D. H. Levy, and T. A. Miller, J . Phys. Chem., 71, 2372 (1967), (5) J. M.Hendrie and P. Kusch, Phys. Rev., 107,716 (1957). (6) K. D. Bowers, R. A. Kamper, and C. D. Lustig, Proc. Roy. Soe. (London), A251,565 (1959). (7) P. Cornaz, H. Choffat, M. Parot, and J.-P. Borel, “Physics of Non-Crystalline Solids,” J. A. Prins, Ed., Interscience Publishers, Inc., New York, N. Y., 1965,p 207.
MATERIAL^ RESEARCH LABORATORY PENNSYLVANIA STATEUNIVERSITY UNIVERSITY PARK, PENNSYLVANIA
L. K. KEYS
16802
RECEIVED APRIL7, 1967
Reply to “Comment on Electron Spin Resonance of
016-017,
017-01s, and O18-0l6”
by Carrington, Levy, and Miller
Sir: Recently we reported the observation of several
A Comment on the Steric Factor Approach to Translational-Vibrational Energy Transfer
low-field electron spin resonance peaks in gaseous 0 2 . l Sir: In many theoretical treatments2 of vibrational Based upon simple considerations of the vector model excitation of a diatomic molecule B-C colliding with of the atom,2 we have interpreted these as possible atom A (or one end of diatomic molecule A-D), the 016-017, 0’7-018, and 0l6-Ol8 absorption peaks. More initial relative A,B-C velocity vector VA, or an effective quantitative studies of these peaks have been carried V A , ~ is considered directed toward the B-C center of by Tinkham and Strandberg,3 who observed a large mass. Approximations2 are introduced so that the number (also subsequently observed by the author) in vibrational energy transfer to B-C averaged over e,4 this same field region. These esr peaks have been inthe angle between the B-C axis and VA, is obtained by terpreted as 0 l6-0l6transitions from considerations of multiplying the collinear (0 = 0) energy transfer value detailed calculations correcting for the various effects by a steric factor u less than unity.2 We show that as mentioned in the previous comm~nication.~ this steric factor approach cannot be generally correct. While these results seem to weaken the previous We have obtained exact numerical solutions to the interpretation’ of these lines, the disagreement between classical equations of motion, with A,B,C restricted to the various investigators apparently indicates, however, that the more quantitative treatment cannot be (1) Research performed under the auspices of the U. 9. Atomic rigorous.y applied. Hendrie and Kuschs have obEnergy Commission. tained from independent measurements at low(2) See, for instance: (a) K. Takanayagi, Progr. Theoret. Phys. S U P P L25,1 (1963); (b) K. F. Herzfeld and T.A. Litovitz, “Absorp field strengths by a molecular-beam method. These and Dispersion of Ultrasonic Waves,” Academic Press Inc., results are not in accord with those of ~ i ~ and k h tion ~ N. Y., 1959,Chapter 7 ; (0) K. F. Herzfeld and V. Griffing, New~York, J . Phys. Chem., 61,884 (1957); (d) C. B . Moore, J . C h a . Phys., 43, Strandberg. More recent studies by Bowers, et u Z . , ~ 2979 (1965). a repeat of the work of Tinkham and Strandberg, (3) Takanayagi (ref 2a) employs the quantum analog of an “effeoproduced results in disagreement with both of the t,ve in his MWN approx~ation. previous investigations. According to these results, (4) Or the appropriate quantum mechanical operation. vAp$
Volume 71, Number 7 Juns 1967
