and Stickney’s Figure l1was in fact one basis for our earlies conclusion.2 There is no question that the ~ u a s ~ - e q ~ l model, ~ b r ~ with ~ m WFe and F assumed as the dominant products, predicts a decrease in reaction probability above some intermediate temperature-in qualitative a g r e e ~ e r ~with t our experimental data.2 B5oiTever, in our opinion, too many additional factors are involved in the turigsten fluorination reaction to be content with the qualitative agreement pointed out by Abbott and Stickney. Thus,e (i) the complex temperature dependence of the W removal rate (more than one local maximum), (ii) the inadequacy of thermodynamic: data for the tower fluorides (WF,(g), n .< 6), and (iii) the msgnttude of the observed peak W atom removal probaJbility2 (enrax > 1/8; see especially the Mo/F data of re%a), when combined with the QE underpredictiorn of sates (in the only portions of Figure 1 of ref I which are honufide predictions) seem to us to preclude WPs(g) as the only significant W-containing product, especialLy above 2000°K. Moreover, it is significant thac the $E underpredictions of rate above 2000°K (well over three decades at 2500°K) far exceed discrepancies that could reasonably be attributed to experimental tmcertainties in (i) reactant arrival rate, F6(g) thermochemical data, and/or (iii) oxygen impurity level. Without more complete thermodynamic data for the gaseous tungsten fluorides and/or product distribution measurements for this and similar reactions it IS difffcult (i) to decide on the accuracy of QE in the W-F2 reaction and (ji) to answer the more subtle question of whether the assumptions underlying QIC models3%* break down for atom-metal reactions in which product formation by Rideal-Eley elementary steps may play an j mportant role.5 indeed, the use of atomic reactants to study the gasification kinetics of refractory solids6i7 could shed light on this interesting question.2 (1) P. C. Abbott and R. E. Stickney, J. Phys. Chem., 75,2930 (1971). (2) D. E. Rosner and H. D. hllendorf, ibid., 75, 308 (1971). (3) J. C. Batty and R . E. Stickney, J . Chem. Phus., 51,4475 (1969); see also J. E. Franklin and R . E. Stickney, High Temp. Sci., 3, 401 (197 1) (4) J. C. Batty and R. E. Stickney, Ozid. Metals, 3,331 (1971). (5) D. E. Rosner and €3. D. Allendorf, J. Electrochem. Soc., 114, ,306(1967). (6) D. E. Rosner and N.D. Allendorf, Proc. Int. Symp. High Temp. Techn., j96‘9,707 (1969). ;7) D. E. Rosner and N. D. Allendorf in “Heterogeneous Kinetics at Elevated Tempera-cmes,” Plenum Press, New York, N. Y., 1970, pp 231-251. ~
DEPARTMENTOF ENCHNEERINQ AND APPLIED SCIENCE YALE UNIVERSITY NEWHAVEN,CONNECTICUT 06520
DANIEL E. ROSNER* PAUL C. NORDINE
RECEIVED SEPTEMBER 13, 1971
Optical Absorption of Solvated Electrons in Alcohols and Their Mixtures w i t h ~
~
k
~
Publication costs aasisted by the U. S. Atomic Energy Commission‘
Sir: As noted by other^,^-^ the dc:ohok and their mixtures, especially with alkanes, are ~ a ~ t ~ c : ~suitlar~y able media for study of the factors that in formation, structure, and decay of solvated electrons. We have initiated a broad and thorough atllzdy of the time dependence of solvated electron a,bsorption spectra in such media. The initial results of that study are of special interest and significance in rrlat1oi.i t o certain previously published experimental viork294-6 and m o d e l ~ l * - ~for ~ the solvated electron. Absorption spectra have been determined for the solvated rlectron in 22 alcohols (for 15 of which i,he eS- spectrum has not been reported) and in binary mixtures of a number of alcohols and cyclohexane. Soriie qalierrt aspects of the results are reported in this ~ o n ~ ~ ~ ~ ~ ~ c a ~ The best avnilable grade of each alcohol TVBS purified by distillation wit,R a Nester-Faubt spinning-band column. Water content of an sllcohol ~ B V F I ’exceeded 0.2% and generally was less than Certified cyclohexane was used witlaou fication. Solutions were deaerated by aiitrogeri bubbling and irradiated in 1-em quartz c d a a t --.30” with 5or 10-nsec pulses of - J S - M ~ V eiiectroras (estiraated dose per pulse of -1019 eV from bhe Notre Arco Model LP-7 linear accelerator, The light for rnensurement of +,heoptical absorption1 wn,s a 450-W xenon lamp (Ushio UXL 451-0) that was p d s e times the steady-state output Cor a 5-anwc period within 11hich the absorption WRS recorded. Trans(1) The Radiation Laboratory of the Univcrsaty of Notre Dame is operated under contract with the U. S Atomic Energy Commission. This i s AEC Document No. COO-38-851. (2) M. C. Sauer, Jr., S. Arai, and 1,.M. Dortman, J . Chem. Phys., 42,708 (1965); 1,. M . Dorfman, Adaan. Chem. Ser., Mo,SO, 36 (1965). (3) S. Arai and M C Sauer, Jr., J . C h ~ mk“h$,s., . 44, 2297 (1966). (4) T . J. Kemp, G, A. Salmon, and P.Wardman in “Pulse Radiolysis,” M. Ebert, J. P. Keene, A. J. Swallow, and J . W Baxendale, Ed., hcadeniie Press, London, 1965, pp 247-287. (5) B. J. Brown, N. T Barker, and D, F. Bangster, J . Plays, Chem., 75,3639 (1971) (6) L. B. Magnusson, J. T. Richards, and J, K Thomas, I n t . J . Radiat. Fhgs. Chem., 3,295 (1971). (7) J. X-P. Baxendale and P. Wardman, N a t w e (London), 230, 449 (1971). (8) J. T. Eichards and J. I 2000 nmle). Clearly, such resulbs arc not compatible with dielectric cont'inuum models but are icompatible with the suggested predominance of the sole of a solvation domain. The transition euergy is {determined by composition of the solvation domain. 'The equilibrium composition of the solvation domaiii is determined by (1) composition of the hinary mixture, ( 2 ) relative strength of the attractive interactions of ewith the mixture components (reflected by E",, of the neat) components), arid (3) strength of the attractive interactions between the mixture components. For alcohol--aikane mixtures in which there is weak int)eraction between the components and a large difference in the strength of their interactions with e-, the solvation domain rcmains essentially saturated with alcohol own to very low concentrations. However, for binary mixtures in which the interaction between components is strong or the difference in strength of their interactions with e - is small or both, a different dependence of the solvation domain composition and, Lherefore, of E,,, on solution composition is to be expected.14 In the mixtureti studied, as in the neat alcohols, the
2933 e*- spectra are present within the 5-nsec pulse and do not change over a t least a 20-nsec period. Clusters of alcohol molecules exist in alkane solutions even a t 8.1 M alcoholl7 and provide a distribution of preexisting sites of diverse compositions for trapping (localization] of the thermalized electrons. Evidently, relaxation of such trapped electrons to the equilibrium composition and configuration of es- is complete xithin 5 nsec in the 0.1 M solutions of alcohol in cyclohexane. Such an observation ie in accord with recent calculations by h!Iozumderl* on t)he time dependence of electron solvation as a function of the concentration of single dipole molecules randomly dispersed in a nonpolar medium. For elucidation of the solvation ~ e c ~ ~ ~ n i s m in alcohol-alkane mixtures, the studierj are being extended to lower alcohol concentrations, Blkaaes of greater viscosity, lower temperatures, and shorter times (for which purpose we have deveioped new infrared picosecond pulse-radiolysis sgstcnn utilizing an injection laser diode).
ROBERT R. HENTZ*
DEPBR'TMENT O F CHEMISTRY A N D
GERALDINE KENNEY-NTa4LLACE
T H E l%ADfATION LABORATORY
UNIVERSITI~ OF WOTRE DAME NOTRE D A M E , INDlANA
46556
RccsivEu MAY26, 1973
Calculation of
AHdO ( g )
- AHd'(1)
for Dissociating
Dimers wia the "Dissociation-Vaporization" Rule. The AHdo (1) of Trimethylaluminum Publication costs assisted b y the Ethyl Corporation
Sir: For dissociating dimers such as the aluminum alkyls, both the heat of dissociation in the liquid phase (AHd'(1)) and that in the gaseous phase ( A H d o ( g ) ) are of considerable interest. Since it i s often the case that one of these quantities is known, but not the other, a method of calculating one value from the other would be very useful. For example, the A N d o ( i ) for trimethylaiuminum (TMA), often needed for the interpretation of kinetic data, has not been determined experimentally. It would be very helpful if A H d o ( l ) could be derived from the experimental value for AHdo(g)(20.40 lical/mol of dimer'), (1) C. H. Henriclcson and D. P. Eyman, Inorg. Chenz., 5 , 1461 (1967). The JournaE of Physical Chemistry, Vol. 7 6 , N o . BO, l 9 7 e
