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305
Charge-Transfer-to- Solvent Spectra in Liquid Ammonia
260 /-\
'
I
280 I
I
300
320
3LO
by Dan Shapka and Avner Treinin Departnzent of Physical Chemistry, Hebrew University, Jerusalem,,Israel (Received August 84, 19/36)
The effect of solvent on the absorption spectrum of solvated electrons has recently been investigated,l and it was shown that hvmax of esolmight be predicted by using the c.t.t.s. scale.2 The c.t.t.s. value of liquid ammonia (ie., the transition energy of I- in this solvent at 20') is of special interest for this purpose, and the value 105.9 kcal./mole was derived3by extrapolation of low-temperature data. It was furthermore concluded that the shift in the band maximum of Ion going from water to ammonia is very similar to that of solvated ele~trons.~We wish to report the results of studying the spectrum of I- in liquid ammonia at various temperatures up to 55'. A modified c.t.t.s. value of ammonia is derived. In addition, new information is presented on the spectra of CNS- and NO3- in this solvent. Experimental Section
The liquid ammonia used (Matheson anhydrous) was dried over sodium and further pufied by successive vacuum distillations from the sodium solution. For measuring the spectrum at the boiling point of NH,, the procedure followed was similar to that of Jolly6 with a l-mm. absorption cell. For higher temperatures we used a high-pressure l-cm. absorption cell made of Hasteloy Type C alloy with 10-mm. thick quartz windows, designed for pressures up to 150 atm. (Research and Industrial Instruments, London). To prepare a ca. lo-' M solution of KI or NE1;CNS the appropriate amount of aqueous solution was introduced into the cell, and the water was expelled by evaporation under reduced pressure. The salt was thoroughly dried under vacuum, and ammonia was then distilled into the cell which was kept at about -60'. After being filled it was tightly stoppered. A special thermostated cell compartment was designed suitable for use with the Hilger Uvispec spectrophotometer, the temperature being kept constant within *0.5'. The spectra were measured against air and corrected for the spectrum of ammonia which was taken under the same conditions. To check the concentration, after the measurement the ammonia was evaporated, water was introduced into the cell, and the spectrum of the aqueous solution was measured.
-
l / h rl0-4c"-'
Figure 1. The absorption spectra of I-, CNS-, and NOain liquid ammonia a t various temperatures. Curves 1-3: NHaNOs (-0.1 M ) a t -33.4, 20, and 68", respectively; M ) a t -33.4, 20, 28.6, 37.5, 46.5, and curves P 9 : KI ( 54", respectively; curves 10-12: NH&NS ( M ) a t 20, 46.5, and 54.2", respectively. At -33.4" (dashed curves) the intensities could not be accurately determined.
Results and Discussion Figure 1 shows some of the spectra obtained. It appears that on going from water to ammonia, the spectrum of I- though considerably red shifted hardly changes its shape: at 20' emax 1.36 and 1.23 X lo4 M-l em.-' and AvL/*(half-width) 4.25 and 4.54 X lo3 cm.-l, in water6 and ammonia, respectively. This indicates that the nature of the electronic transition is essentially the same in both solvents. Throughout the whole range studied hv(I-)max varies linearly with temperature (Figure 2); K = -dv/dT = 23.2 cm.-l deg.-l. This is considerably smaller than the value previously rep~rted.~JThe new c.t.t.s. value of liquid ammonia is 108.1 kcal./mole, which is still the lowest hitherto observed (the highest value 133.5 kcal./mole is displayed by glycerols). Thus, the solvent sensitivity of the iodide spectrum is somewhat smaller than that of solvated electrons. The effect of liquid ammonia on the c.t.t.s. band of CNS- resembles that on I-. This is clearly shown in (1) M. Anbar and E. J. Hart, J. Phys. Chem., 69, 1244 (1966). (2) I. Burak asd A. Treinin, Trans. Faraday SOC.,59, 1490 (1963). (3) T.R. GriEths and M. C. R. Symons, ibid., 56, 1125 (1960). (4) M.J. Blandamer, R. Catterall, L. Shields, and M. C. R. Symons, J . Chem. SOC.,4367 (1964). (6) W.L. Jolly, U.C.R.L. Report 2008, 1962. (6) G.Stein and A. Treinin, Tram. Faraday SOC.,55, 1091 (1959). (7)The pressure in the cell did not rise above 30 atm. This rise could have relatively very little effect on the spectrum: M. J. Blandamer, et al., Trans. Faraday SOC., 59, 1748 (1963). The constancy of K further supports this conclusion. (8) T. Feldmann and A. Treinin, unpublished results.
Volume 70, Number 1 January 1966
NOTES
306
Relative to the aqueous solution ammonia brings about a red shift of only -lo00 cm.-I, which is accompanied by decrease of intensity. This is the regular response of the band to solvent eflects.IO ~ P ( N O ~ - ) , , ~ is hardly affected by temperature, but the intensity is markedly affected (Figure 1). The decrease of intensity with increase of temperature also occurs in dimethylformamide and aqueous solutions, and it was ascribed to weakening of hydrogen bonding or dipolar effects.ll Some vibrational structure appears at low temperatures.
Acknowledgmnt. We gratefully acknowledge the support of this research by the U. S. Army (Contract DA-91-591-EUC 3583).
- 20
0
20 A0 temperature ("C)
(9) E. Gusarsky and A. Treinin, J . Phys. Chem., 69, 3176 (1966). (IO) E.Rotlevi and A. Treinin, ibid., 69, 2646 (1966). (11) S. J. Stickler and M. K d a , "Moleculsr Orbitals in Chemistry, Physics and Biology," Academic Press Inc., New York, N. Y.,1964, p. 241.
60
Figure 2. The variation of 1/XmSx of I- and CNS-- with temperature.
Polymer Configuration at an Adsorbing Interface by the Monte Carlo Method
'"i
by Sydney Bluestone and Charles L. Cronan' Depart& of CherniStry, F r e m State College, Freano, Cdiforniu (Received August 86, 1966)
E 121
Y
7
.c
I
I
loa
I
I
1
110
112
114
.hv
I 116
I 118
I
,kcol/mol
Figure 3. hv, of CNS- us. hvmX of I- in liquid ammonia, acetonitrile, and acetonitrilewater mixtures (the weight per cent is recorded); t = 20".
Figure 3 where hv,,, of this band in a few solvents (in which the band is clearly separated from the overlapping transition) is plotted against their c.t.t.s. values. By extrapolation we obtain for the energy in water ~Y(CNS-)~,,= 4.59 X lo4 cm.-'. For K (CNS-) the value 18.9 crn.-I deg.-l is obtained (Figure n\
AI.
A completely tSrpe Of effect exhibited by the low-intensity internal tramition of NOa-. The Journal of Physical C h i S t r u
Several r e p ~ r t s ~have - ~ been published dealing with the shape of a long chain polymer at an interface. The adsorbed polymer can be described either as a thick film4with large loops, extending far into solution, and with only a few chain segments adsorbed, or as a thin film28-sconsisting of small loops, confined rather close to the adsorbing interface, with a large fraction of the segments adsorbed. I n the present study an IBM 1620 I1 digital computer was used to perform Monte Carlo calculations in order to establish what the film thickness is under various adsorption potentials. The method employed was that of Verdier and Stockmayeld (VS), used previously by Bluestone and Vold (1) This paper is baaed on a thesis submitted by C. L. Cronan to the faculty of Freano State College in partial ful6llment of the requirements for the undergraduate course, Independent Study 190. (2) (a) H.L.Frisch, J . Phys. Chm., 59, 633 (1966); (b) W.I. Himchi, ibid., 65, 487 (1961). (3) A. Silberberg, ibid., 66, 1872, 1884 (1962). (4) R. Simha,H.L. FiSoh, and F. R. Eirich, ibid., 57, 684 (1963). (6) P. E. Verdier and W. H. Stockmayer, J . Chem. Phys., 36, 227 (1962).
