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us. l/(No - N) plot to be maintained as observed k and
argon (Ar/XCCl3 = 200-500) were simultaneously condensed with an atomic beam of lithium (Li/ XCCl3 = '/z, 1, or 2) on a cesium iodide window a t 15"K, as described by Andrews and Pimentel.6 Infrared spectra were recorded in the 200-4000-~m-~spectral region. I n the carbon tetrachloride experiments using 'Li, intense bands a t 579 cm-', which shifted to 617 cm-' with 6Li, were recorded. The former absorption agrees with 580 cm-l reported by Schlick and Schnepp7 for lLiCl while the latter is higher than the 608 cm-' assigned by these workers to 6LiC1. However, the 617cm-' absorption is intense (0.28 OD) and its assignment to 6LiCl appears to be certain. When bromotrichloromethane is used as a precursor with "i, the 617cm-' band and one at 541 cm-' corresponding to Schlick and Schnepp's assignment of 540 cm-' to 6LiBr were recorded. Obviously, lithium reacts with the halomethanes to produce lithium halides under the conditions of the experiment. I n every carbon tetrachloride experiment an intense band (1.1 OD, vlI2 = 2 cm-l) a t 898 cm-l was recorded. I n a separate experiment using a 51% 13C-enrichedcc14 sample, an intense (1.2 OD) well-resolved doublet with components of equal intensity a t 898 and 869 cm-' was (7) J. A. McMillan and S. C. Los, Nature, 206, 806 (1965). observed. Spectra for the BrCC4 experiments showed (8) K. E. Larsson, V. Dahlborg, and 5. Holmryd, Arkiv Fysik, 17, an intense (1.1 OD) doublet a t 898 and 888 cm-l. 369 (1960) : discussed in "Thermal Neutron Scattering," P. A. Egelstaff, Ed., Academic Press, New York, N. Y., 1965, Chapter by These absorptions show no detectible lithium isotope K. E. Larsson. effect and they decrease in intensity with respect to an DEPARTMENT OF CHEMISTRY C. A. ANGELL absorption due to a species containing lithium when the PURDUE UNIVERSITY E. J. SARE Li/CCI4 ratio is increased. INDIANA 47907 LAFAYETTE, R. D. BRESSEL Spectra of samples of C2C16and C2C14in argon were RECEIVED MAY5, 1967 recorded. The absorptions a t 898 cm-' are not due to a known stable chlorocarbon species. After sample warming to 47"K, the 898-cm-' absorption intensity decreased while the C2C&band appeared a t 684 cm-'. Infrared Detection of Trichloromethyl The well-resolved doublet near 900 cm-' in the 51% Radical in Solid Argon 13C-enriched CC14 experiment suggests that a single carbon atom is present in the molecular species responsiSir: The trichloromethyl radical is suggested to be a ble for the absorptions, where the resolved components photolytic decomposition product of carbon tetraat 898 and 869 cm-I are due, respectively, to the 12Cand chloride' and bromotrichloromethane2 and an interl3C species. Unfortunately, chlorine isotope shifts are mediate in the reaction of bromine with bromotrichlorotoo small (2-3 cm-') to resolve. CC1 absorbsa near methane. We are not aware of any previous direct spectroscopic (1) B. C. Roguitte and M. H. J. Wijnen, J . Am. Chem. SOC.,85, evidence for the trichloromethyl radical. Since the 2053 (1963). matrix reaction between lithium atoms and methyl (2) J. M. Tedder and R. A. Watson, Trans. FaTaday SOC.,6 2 , 1215 (1966). halides has produced sufficient methyl radicals for infra(3) N. Davison and J. H. Sullivan, J . Chem. Phys., 17, 176 (1949); red spectral s t ~ d y ,we ~ ,have ~ applied this technique to A. A. Miller and J. E. Willard, ibid., 17, 168 (1949). XCCl, molecules in an attempt to study the trichloro(4) W. L. S. Andrews and G. C. Pimentel, ibid., 44, 2527 (1966). methyl radical. (5) L. Andrews and G. C. Pimentel, ibid., submitted for publication. Samples of carbon tetrachloride, 51% 13C-enriched (6) W. L. S. Andrews and G. C. Pimentel, ibid., 44, 2361 (1966). carbon tetrachloride, or bromotrichloromethane in (7) S. Schlick and 0. Schnepp, ibid., 41, 463 (1964).
Q probably remained proportional rather than constant. However, the slope of the linear plot was determined mainly by the high concentration points, where k was measured experimentally, so dT,/dN should correspond with Q in this region. Figure 1 shows this is gratifyingly close to correct. Of even greater interest is the temperature to which the curvilinear plot extrapolates a t zero concentration. This temperature, 140 f 5"K, is in excellent agreement with the value of T, of 139°K observed by McMillan and LOS' in the warm-up of vapor-deposited vitreous ice. Noting that T$T0 a t R = 4 is 1.09 we arrive a t an estimate of Tofor water of 128 f 5°K. The neutron scattering data of Larsson, et aE.,8have been interpreted to yield an effective Debye temperature for the collective vibratory motions in water of -130°K. While the coincidence with the value of To may prove fortuitous, the implication that the glass transition is related in some way to a rapid increase in the importance of multiphonon scattering processes in the glassy solid deserves serious examination in view of its potential importance to the understanding of liquid-solid relations.
Volume 71, Number 8 July 1967
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845 cm-', so we are left with CC12and CCla as possible choices. The former seems a less likely possibility since it would require two abstractions from the same parent, but the data do not preclude this possibility. Both LiBr and LiCl were observed in the BrCC4 experiments, which suggests that both c c l and ~ BrCC12 radicals were formed. The observed spectra are consistent with this proposal since we expect the CCl2 stretching vibrations in BrCC12 to be shifted slightly to lower frequency from the same vibration for CC&. Production of the series of radicals CC13, BrCC12, Br2CC1, Br3C should clearly define the number of chlorine atoms present in the 898-cm-' absorber. Additional information on the 898-cm-l absorption is provided by normal-coordinate analysis, which requires the assumption of a molecular structure. Methyl radical is planar,Bbut trifluoromethyl is pyramidal with an F-C-F angle near tetrahedral,1° and we expect trichloromethyl to be more nearly like its fluorine counterpart. If CC1, has this Csv symmetry, the 898cm-' absorption might be v3 ( E ) since it is in the C-C1 asymmetric stretching region. Since u4 ( E ) , the nsymmetric bending mode, is expected around 200 cm-l, we expect the separation of high and low frequencies" to be a reasonable approximat,ion. This calculation gives F33 = F , - F,, = 3.385 mdynes/A for 13CClaand 3.395 mdynes/A for 12CCls. The agreement is within
The J O U Tof ~P h y s i d Chemistry
the approximations involved and frequency uncertainties. (Unfortunately, the G matrix element for U S of CClz has the same value, so this calculation cannot choose between CC12and ccl3.) The use of two different chemical precursors and the isotope shift, together with the detection of the lithium halides and hexachloroethane on warm-up, show that the 898-cm-' absorption is probably due to CCh. The v 3 assigned here to CC13is higher than U S of CCla of 788 cm-l and near v g of C2C14of 915 cm-l in solid argon. This fact has interesting implications as to the bonding and structure of CC1, which will be discussed, along with the search in progress for other absorptions of CCla, in a later publication. ~~
~
(8) G . Hersberg, "Spectra of Diatomic Molecules," 2nd ed, I). Van Nostrand Co., Inc., New York, N. Y., 1950. (9) G . Hersberg, Proc. Roy. Soc. (London), A262, 291 (1961). (10) R. W.Fessenden and R. H. Schuler, J . Chem. Phys., 43, 2704 (1965). (11) E. B. Wilson, Jr., ibid., 9 , 76 (1941).
DEPARTMENT OF CHEMISTRY AND CENTERFOR ADVANCED STUDIES UNIVERSITY OF VIRGINIA CHARLOTTESVILLE, VIRGINIA
RECEIVED MAY15, 1967
LESTERANDREWS
