J. Phys. Chem. 1902, 86, 327
327
Solvated Electron Optical Absorption Spectra in Liquid Methylamine C. M. Stupak, 1. R. Tuttle, Jr.;
and Sidney Golden
Department of Chemistry, Brandeis University, Welthem, Massachusetts 02254 (Received: November IO, 198 1)
Solvated electron optical absorption spectra in liquid methylamine have been obtained by extrapolating relative absorbance data obtained from dilute lithium solutions to infinite dilution in lithium. These spectra are shown to be identical within experimental error with solvated electron spectra determined by using pulse radiolysis. Also, within experimental uncertainty all of the spectral profiles of solvated electron spectra in methylamine display shape stability. The effective number of solvent molecules which serve to localize the electron in methylamine is determined to be 0.83. We have obtained optical absorption spectra of lithium solutions of various concentrations in methylamine at -50, -70, and -90 "C. By plotting the relative absorbances A(v)/A,, at each frequency Y as a function of the maximum absorbance value A,, and extrapolating to A , = 0, we further obtained the absorption spectra at infinite dilution. The relative absorbances proved to be virtually independent of A , for each v. The resulting solvated electron spectra and those which have been obtained by using pulse radiolysis' have been shifted as described previously2 and are plotted on a common reference frequency scale in Figure 1. It is seen that (1)the solvated electron spectra obtained by using pulse radiolysis' and those obtained from measurements on metal solutions are identical within experimental error, and that (2) solvated electron spectra in methylamine display shape stability within experimental error over the temperature and frequency ranges investigated. The latter point was made earlier but with a more limited set of data which extended over a smaller frequency rangee2 Values of the frequency of maximum absorption,,,,v the half-height width, the shift used in comparing the spectra plotted in Figure 1, and the root-mean-squared deviation between the shifted spectrum and the reference spectrum, 6, are given in Table I for each of the shifted spectra plotted in Figure 1. Values of 6 measure the extent of agreement between solvated electron spectra obtained from measurements on lithium solutions and those obtained by using pulse radiolysis, as well as of the extent to which spectral shape stability23is maintained in the two studies. A linear least-squares plot of,v vs. temperature for all the data yields a straight line within experimental error. The dope of the line gives a temperature coefficient of 28 cm-'/K for Y-. This yields a value of 0.83 for the (1)W. A. Seddon, J. W. Fletcher, and F. C. Sopchyshyn, Can. J. Chem., 56, 839 (1978). (2) T. R. Tuttle, Jr., and S. Golden, J. Chem. Soc., Faraday Trans. 2,77,873(1981).The procedure used in comparing the different spectra is described here. (3) S. Golden and T. R. Tuttle, Jr., J. Chem. Soc., Faraday Trans. 2, 77,889 (1981).
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Flgure 1. Comparison of solvated electron optical absorption spectra 183 K, this in methylamine on a reference frequency, v', scale: (0) work; (0)203 K, this work; (A)223 K, this work; (). 184 K, ref 1; ( 0 ) 208 K, ref 1; (A)241 K, ref 1. Shifts requlred to superimpose spectra and rootinean-squared deviations from reference spectrum are given in Table I.
TABLE I: Band Parameters for Solvated Electron Optical Absorption Bands in Methylamine
T/K 183 184 203 208 223 241
vmaxl
cm-'
a
b
fiC
ref
8676 8683 8012 7775 7586 7053
4636 (4799) 4661 (4427) 4734 (4656)
0 108 -530 -700 - 990 -1344
0 174 65 110 110 135
this work 1
this work 1
this work 1
Width at half-height in c m - ' . Values in parentheses required extrapolation of the data for their determination. Band shifts in cm" used in preparing Figure 1. Rootmean-squared deviation in cm-' between shifted band and reference band at 183 K. a
effective number of solvent molecules involved in localizing the solvated e l e ~ t r o n . ~ (4)S.Golden and T. R. Tuttle, Jr., J. Chem. SOC.,Faraday Trans. 2, 77,1421 (1981).
0 1982 American Chemical Society
