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3377
KD.AB= (KD,AKD,B)=
(3)
follows immediately from eq 2 since the standard free energy changes are logarithmically related to equilibrium concentrations of the reacting species. Therefore, eq 1 reduces to
KABI'IKAB'= (KD,AKD ,B)a-1
(4) (2) Upon differentiating eq 2 with respect to temperature, one obtains AHOAB
I+II
= CY(AHOA 1-11
+
(5)
A H O B )
1-11
Similarly, differentiation of (4) yields
AH"'^ -
AHOI =
+
I+II
1411
(6)
where A H O I and AHOII are the standard enthalpy changes for the association reaction in solvents I and 11, respectively. Related equalities can be derived for the standard entropy changes. I n order to test and apply these relations, it is convenient to examine eq 4. This relation predicts that a plot of log KABus. log (KD,AKD,B) for a series of solvents will be linear with slope equal to a - 1. For convenience, the distribution constants are calculated with reference to the particular solvent for which KAB is largest. By definition, KD,Aand KD,Bare equal to unity for the reference solvent; the product, KD,A* KD,B,is expected to be greater than unity for each of the other solvents. A plot of this type is shown in Figure 1 for the reaction: water (A) pyridine (B) = pyridine monohydrate (AB), which has been studied in detail in this laboratory.2 The points corresponding to the various solvents lie nearly on a single straight line having a slope of 0.29; hence, a = 1.00 - 0.29 =
+
i
I 1-
3
30
10 %,A
100
3CO
Ks,a
Figure 1. Correlation of association and distribution constants for the reaction: water pyridine = water-pyridine at 25": I, cyclohexane; 11, carbon tetrachloride; 111, toluene; IV, benzene; V, 1,2-dichloroethane. Indicated uncertainties in K A Bare standard errors.
+
Acknowledgment. This work was supported by the United States Department of the Interior, Office of Saline Water. (2) J. R. Johnson, P. J. Kilpatrick, S. D. Christian, and H. E. Affsprung, in preparation.
DEPARTMENT O F CHEMISTRY
- l ) ( A H o ~ AH'B)
(CY
0.71. The linearity of the plot indicates that a single value of a suffices to correlate the effects of solvents having a wide range of properties. As the solvent is varied from cyclohexane to 1,2-dichloroethane, the product KD,AKD,B increases by a factor greater than 300.
THEUNIVERSITY OF OKL.4HOMA NORMAN, OKLAHOMA73069
SHERRILD. CHRISTIAN JAMES R.JOHNSON HAROLD E. AFFSPRUNG PAUL J. KILPATRICK
RECEIVED AUGUST18, 1966
Chemiluminescent Gas-Phase Reactions Involving Electronically Excited Oxygen Molecules. Trimethylaluminum and Diborane near 3 mtorrl
Sir: It is known2 that some 10% 02(a1A)and 0.1% 02(b1Z) are present together with 0 atoms in the products of a microwave discharge through 02. Chemiluminescent reactions involving these excited molecules have been observed at -1 torr.3 Because of the presence2g4of these 02 species in the upper atmosphere, it is of interest to establish whether they can produce a detectable chemiluminescence at pressures in the millitorr range encountered in that medium. We wish to report such reactions involving (1) trimethylaluminum (TMA) and (2) B2Hs. The former does not require the participation of 0 atoms, and the latter does. The products of a 2450-MHz discharge at 0.8 torr in an 1.1-cm i.d. Vycor tube through (1) 95% Ar-5% 0 2 and (2) 100% 0 2 were expanded, 40 cm downstream from the discharge, through a sonic orifice into a 15-cm i.d., 130 cm long Pyrex pipe where they were mixed with TMA, B2H6, or NO.5 A Teflon baffle plate located (1) This work was supported by the NASA Langley Research Center under Contract NAN-5035. (2) L. W. Bader and E. A. Ogryzlo, Discussion Faraday SOC.,37, 46 (1964); R. E. March, S. G. Furnival, and H. I. Schiff, Photochem. PhotobioE., 4, 971 (1965). (3) S. J. Arnold, N. Finlayson, and E. A. Ogryslo, J . Chem. Phys., 44, 2529 (1966). (4) H.P.Gush and H. L. Bui~s,Can. J. Phys., 42, 1037 (1964).
Volume 70, Number 10 October 1966
3378
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EDITOR
addition; this increase was accompanied by a faster decrease in I, which had the value 0.3 aiu at the downstream end of the reaction tube for the flow conditions of both columns 2 and 3. Chemiluminescence has been observed upon release of TMA in the upper atmosphere.’ The present results suggest that this glow, at least in part, can be caused by 02(a1A) molecules. &He needed 0 atoms for the chemiluminescent reactions to be initiated since no emission was observed in the presence of the HgO mirror. Addition of increasing amounts of 02(X32)strongly and continuously enhanced the initial I without causing a noticeable Table I: Observed Intensities”** decrease downstream. Comparison of columns 3 and 4 of Table I shows that the excited 0 2 molecules Discharge type Ar + 0% are more efficient than ground-state 0 2 in producing with 0 2 with ] this enhancement. Based upon [02(a1A)I/ [02(X3Z) Reagent Ar + 02 Ozaddedc 02 HgO mirror = 0.1, 02(a1A) can be shown5 to be about a factor of TMA 0.4 1 20 330d 10 more efficient (assuming the contribution of Or 300
