Journal of the American Chemical Society
5834 I
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process of decomposition in methylene chloride a t -85 O C in FEP tubing. This 19F N M R spectrum shows a peak a t 6 -9.6 ppm relative to CFC13 with two side bands indicative of the xenon-1 29 isotope (spin = l/2,26.44% natural abundance). The ‘9F-129Xetwo-bond coupling constant observed for this is 1940 Hz. This is smaller than the one-bond coupling of 5550 H z in XeF26 and larger than the three-bond coupling of 18 Hz in FXeN(SO*F)2.* Confirmation of these observations awaits I9F and I3C or spectra in a suitable solvent.
Acknowledgments. We gratefully acknowledge support of this work in part by the Air Force Office of Scientific Research (AFOSR-78-3658 A), the National Science Foundation, and the Robert A. Welch Foundation. W e also acknowledge the following assistance: the Mass Spectrometry Facility a t Cornell University where the chemical ionization mass spectra were obtained; Professor Richard F. Porter for arranging for these experiments and for helpful discussions on the spectra; Professor Robert Willcott and Ruth Inners for assistance in obtaining the low-temperature I9F FT N M R spectra; Professor Basil Swanson and Dr. J. Rafalko for assistance in obtaining low-temperature IR and Raman spectra.
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References and Notes ( 1 ) N. Bartlett, Proc. Chem. SOC.,218 (1962). (2) R. D. LeBlond and D. D. Desmarteau, J. Chem. SOC.,Chem. Commun.,555 (1974). (3) D. Holtz and J. L. Beauchamp, Science, 173, 1237 (1971). (4) M. Wechsberg, P. A. Bulliner, F. 0. Sladky, R. Mews, and N. Bartlett, Inorg. Chem., 11, 3063 (1972). (5) R. J. Lagow, L. L. Gerchman, R. A. Jacob, and J. A. Morrison, J. Am. Chem. SOC.,97, 518 (1975). (6) K. Seppelt and H. H. Rupp, Z. Anorg. Allg. Chem., 409, 331 (1974). (7) Western Electric Corp., Princeton, N.J.
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Laura J. Turbini,’ Robert E. Aikman, Richard J. Lagow* Department of Chemistry, UniGersity of Texas at Austin Austin, Texas 78712 Receiued February 12, 1979 800
WAVELENGTH (ern-' 1 Figure 2.
tain the spectrum in Figure 2 which has a number of similarities to the spectrum of Hg(CF3)2. A complete vibrational analysis has not yet been possible because decomposition occurs with a Raman laser source. Electron impact mass spectra of the Xe(CF3)z showed peaks for Xe+, )H+ ratio is 10, while that ratio is 1.6 for the Xe(CF3)2 compound. This result is consistent with the thermal decomposition of Xe(CF3)z to XeF2. lsobutane was unsuccessful in producing a chemical ionization spectra. Acquisition of 19F N M R evidence has been greatly hampered by lack of a suitable solvent. Although over 20 solvents have been considered, two categories have been observed: those in which decomposition occurs rapidly, and those (mostly fluorocarbons) in which the new fluorocarbon material is insoluble. In methylene chloride the compound decomposes rapidly to give xenon difluoride and fluorocarbons. A Fourier transform I9F spectrum was obtained very rapidly during the 0002-7863/79/150l-5834$0l .OO/O
Evidence of Vibronic State “Selectivity” in the Photoracemization of Tris( 1,lO- phenanthroline)chromium(111) Ion in Solution Sir. Photoracemization of (+)-tris( 1 ,IO-phenanthro1ine)chromium(ll1) ( ( + ) - C r ( ~ h e n ) 3 ~ +has ) been observed to be partially quenched by 1- and 0 2 , but there is a residual nonquenchable limit which was assigned to immediate reaction from the initially excited 4T state (approximate octahedral microsymmetry) preceding intersystem crossing to the quenchable 2E state.’ Subsequently, it has become clear that intersystem crossing from 4T states in Cr(II1) complexes is a fast (picosecond) p r o c e ~ s and ~ , ~ that intersystem crossing shows wavelength dependence indicating a common time scale for intersystem crossing and vibrational r e l a ~ a t i o n .If~ ,there ~ is a fraction of reaction which proceeds from the quartet prior to intersystem crossing, this reactivity might be expected to occur in competition with vibrational relaxation, i.e. to display vibronic state selectivity. This point can be tested by examining wavelength dependence at high quencher concentrations where only the direct quartet reaction is observed. First-order plots of decay of optical activity of (+)Cr(phen)3C13 were obtained for irradiation at argon ion laser wavelengths of 457.9,465.8,488.0, and 514.5 nm. Data quality and precision is illustrated by the runs presented in Figure 1. The experimental procedure included the following features: (i) ( + ) - C r ( ~ h e n ) 3 ~solutions + were prepared gravimetrically
0 1979 American Chemical Society
5835
Communications to the Editor Table I
[(+)-Cr(~hen)3+~1, (mol X IO3)
A, nm
intensity,O einsteins s-1 x IO7
PH
T , OC
1.050 0.995 0.47 1 4.310 2.730 4.540 0.896 2.490 1.736 5.136
5.8 5.8 5.8 5.8 5.9 6.0 5.8 5.8 3.0 3.0
20 20 20 20 20 90 25 25 20 20
2.05 I .49 1.14 0.75 1.31 2.38 2.74 2.74 1.19 0.56
514.5 488.0 465.8 457.9 457.9 457.9 514.5d 488.0d 5 14.5 488.0
-
quantum yields, % 4rac(Ndb @rac(Csl)X 1 0.0177 f 0.0012e 0.0299 f 0.0015 0.0292 f 0.001 5 0.0353 f 0.0018 0.0372 10.0019 0.03 I6 f 0.0022 0.0160 f 0.0012 0.0270 f 0.0018 0.0327 f 0.0016 0.0367 f 0.001 8
-
1.73 113‘ 2.04 f 12 2 . 1 0 1 12 2.79 f 1 1 2.62 f I O 2.86 f I O 0.9 f 15 1.4 f 15 2.64 f 25 4.09 f 12
Measured using reineckate actinometry. Solution purged with doubly scrubbed N2(CrS04.5H20) to zero *E 4A quenching. [Csl] 3.2 X 10-3 mol dm-3, Le., a concentration of I- ion above that required to quench 2E 4A phosphorescence by >99% (ref I). [Csll-saturated solution with extensive 1- ion association presumably present. Error estimates are maximum spread of reported runs and not average or standard N
dcviations.
1 1
,2160
,2150
-.2140
-.2130
-.2120
-.2110
-.2100
,4080
\
-
4.2090
