J. Phys. Chem. 1981, 85, 1856-1864
1856
The coefficients A , can be calculated from the boundary condition eq 19 m
F(s,o) = C sXp,(o)= em(s-l) x=o
(A41
Inserting eq A4 into eq A3 and taking the derivative with respect to s yields m
aF(s,O)/as = C A,, dC,,-lI2/ds = iiuenn(s-l) (A5) n=O
A, = 1 - 2n l:emsP,..l(s) ds 2 Expanding ems in a power series leads to
Using the parity properties of si and Pn-l,and formulas 8.14.15 and 6.1.18 of ref 20, one can obtain the following expression for An:
Sincelg
(P,(s) is the Legendre polynomial of degree n), one gets m
C A,P,-,(s)
n=l
= -fiuem(s-l)
(A61
+
ais19
+
m
Multiplying both sides of eq A6 by P,,-l(s)and integrating between -1 and +1 yields
Using the orthogonality property Of Legendre PolPomi-
+
where j = n, n 2, n 4, n 6, ..., and r is the gamma function (n = 1, 2, 3, ...). ( x ( t ) ) , the mean number of triplets per micelle a t time t , can be written as ( x ( t ) ) = [(dF/as)ls=i =
C xp,(t) x=l
and from eq 6, ( ~ ( 0 ) )=
AU,
(All)
one obtains finally
c*(t)/co* = ( x ( t ) ) / ( x ( O ) ) =
l I ' , ( s ) P,,(s) ds = 0
m
for m # n = 2/(2n 1) for m = n
-(l/Au) C A,, exp(-'/,kn(n - 1)t) (A13)
+
n=l
one can write eq A7 as
Equation A13 is identical with eq 20 and eq A10 is identical with eq 21 when setting A , = -B,.
(19) Gradshteyn, I. S.; Ryzhik, I. M. "Table of Integrals, Series and Products", 4th ed.; Academic Press: New York, 1980.
(20) Abramowitz, M.; Stegun, I. A. "Handbook of Mathematical Functions"; Dover: New York, 1972.
147-nm Photolysis of Phosphine and Phosphine-d,' J. Blarejowskl and F. W. Lampe' Department of chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802 (Received: December 26, 7980; In Final Form: March 6, 1981)
The 147-nm photodecompositions of PH3 and PD3 result in the formation of Hz(Dz)and PzH4(P2D4)in the gas phase and a solid deposit which is probably a mixture of phosphorous and polymeric phosphorous hydrides (PH), and (PD),. The quantum yields for the gaseous products and for depletion of reactants were measured and were found to increase with increasing pressure of phosphine and to decrease with increasing light intensity. All quantum yields for PD3 are lower than those for PH3. Isotope distribution analysis of the diphosphines formed in the photolysis of PH3-PD3 mixtures indicates that diphosphine is formed principally via combination of PH, (PD,) radicals. A mechanism involving these primary photodissociations is proposed which is in accord with the experimental facts. The thermal decomposition of PzH4at ambient temperature (-300 K) is shown cm3/(molecule s). to be second order with a specific reaction rate of (4.25 f 0.18) X
Introduction The photochemistry of phosphine has been the subject of many studies since the early years of this century: a d much information concerning both the Hg-photosensitized (1) US.Department of Energy Document No. DE-AS02-76ER0341617. (2) A. Smits and A. H. W. Aten, 2. Elektrochem., 16, 264 (1910).
0022-3654/81/2085-1856$01.25/0
and the direct photolysis of PH3 and PD3 has been published by Melville and co-workers3* during the period 1932-37. At that time some problems regarding the (3) H. W. Melville, Nature (London), 129, 546 (1932). (4) H. W. Melville, Proc. R. SOC.London, Ser. A, 138, 374 (1932). (5) H. W. Melville, Proc. R. Soc. London, Ser. A, 139, 541 (1933). (6) H. W. Melville, J. L. Bolland, and H. L. Roxburgh, Proc. R. Soc. London, Ser. A, 160, 406 (1937).
0 1981 American Chemical Society
147-nm Photolysis of Phosphine and Phosphine-d,
photochemically initiated oxidation of phosphine1y8 and deuteriophosphine,6 as well as the kinetics of the Hgphotosensitized exchange of H or D atoms with PD3 or PH,? were alsojesolved. R a m s a ~was ' ~ the first to identify PH2-and PD,(X2Bl) radicals following the flash photolysis of the respective phosphines in the quartz ultraviolet region. Based on the above method of generation of PH2 radicals, their and e m i s s i ~ n ' ~spectra , ~ ~ have been recorded, and the_rotation_alfine structure of the first electronic transition, A2A1 X2B1,h_as been established. Norrish and O14ershaw16found PH(X3Z-) and vibrationally excited P2(X1Zg+)both as secondary products of the flash photolysis of phosphine in the far-UV region. The same authors used flash photolysis to investigate photochemical processes in the PH3-O2 system.16 Welge et al.ll also detected PH2(X2B1,u= 0) and PH(X3Z-,u = 0) in the quartz ultraviolet flash photolysis of PH3, while Becker and Welge18 observed emission from PH(A311i)upon irradiation of PH3 at 124 and 147 nm. DiStefano and co-workerslSz1 examined the luminescence from photofragments formed in the irradiation of PH3 as a function of excitation wavelength (115 < X < 210 _nm)and found emission from vibrationally excited PH2(A2A1)for all excitation wavelengths. The emission from PH(A311i)appears upon irradiation below 159 nm, and it sharply increases for A, < 121 nm. Also, the emission from PH(b'Z+) has been observed when PH3 is irradiated with wavelengths shorter than 147 nm. Sam and Yardley22observed luminescence from PH2(A2A1)and PH(A311i)following the irradiation of PH3 with an ArF excimer laser (193.3 nm). Formation of PH2 corresponds to a simple one-photon dissociation process, while P H is produced in a two-photon process. At low laser intensities the fraction of excited PH3 molecules that gives rise to luminescence is only 0.014. The photolysis with an ArF laser has also been used for the selective removal of v ~ Recently, Larzilliere and PH, as an i m p ~ r i t y ~in~silane. JacoxZ5examined the species formed in the vacuum ultraviolet photolysis of PH3 isolated in an Ar matrix at 14 K. PH2,PH, and P2 were identified on the basis of IR and visible-UV absorption spectra. +
(7)C. N. Hinshelwod and K. Clusius, Proc. R. SOC. London, Ser. A , 129,589 (1930). (8)H.W. Melville, J. Chem. Phys., 2,739 (1934). (9)H. W. Melville and J. L. Bolland. h o c . R. SOC.London. Ser. A ., 160,. 384 ii937). (10)D. A. Ramsay, Nature (London), 178, 374 (1956). (11)R. N. Dixon, G. Duxbury, and D. A. Ramsay, Proc. R. SOC.London, Ser. A , 296, 137 (1967). (12)J. M.Berthou, B. Pascat, H. Guenebaut, and D. A. Ramsay, Can. J. Phys., 50, 2265 (1972). (13)B. Pascat, J. M. Berthou, H. Guenebaut, and D. A. Ramsay, C. R. Hebd. Seances Acad. Sci., Ser. B , 263, 1397 (1966). (14)B. Pascat, J. M. Berthou, J. C. Prudhomme, H. Guenebaut, and D.A. Ramsav. J. Chim. Phvs. Phvs.-Chim. Biol.. 65.2022 (1968). (15)R. G. W. Norrish a n i G. A.Oldershaw, Proc. R: SOC.London, Ser. A , 262, 1 (1961). (16)R. G.W. Norrish and G. A. Oldenhaw, Proc. R. SOC.London, Ser. A , 262, 10 (1961). (17)D. Kley and K. H. Welge, 2. Naturforsch. A , 20, 124 (1965). (18)K.H. Becker and K. H. Welge, Z . Naturforsch. A , 19,1006(1964). (19)G. DiStefano, M. Lenzi, A. Margani, A. Mele, and C. Nguyen Xuan, J. Photochem., 7, 335 (1977). (20)G.DiStefano, M.Lenzi, A. Margani, and C. Nguyen Xuan, J. Chem. Phys., 68,959 (1978). (21)C. Nguyen Xuan, G. DiStefano, M. Lenzi, A. Margani, and A. Mele, Chem. Phys. Lett., 57, 207 (1978). (22)C. L. Sam and J. T. Yardley, J. Chem. Phys., 69,4621 (1978). (23)J. H. Clark and R. G. Anderson, Appl. Phys. Lett., 32,46(1978). (24)J. H. Clark and R. G. Anderson, US. Patent 4 146 449 (Cl. 204157, IR; B OlJl/lO),27 Mar 1979, Application 856348, 28 Dec 1977; Chem. Abstr. 90,18927211(1979). (25)M. Larzilliere and M. E. Jacox, NBS Spec. Publ. ( U S . ) ,561,529 (1979).
The Journal of Physical Chemistty, Vol. 85,No. 13, 1981 1857
Phosphine has been detected as a minor constituent of the atmospheres of JupitermB and Saturn.29i30 Since PH3 absorbs some portion of the solar radiation above 120 nm which reaches into the atmospheres of these planets, many complex chemical processes may be initiated. The knowledge of the photochemistry of phosphine is, therefore, important for understanding the chemistry of these planetary atmosphere^.^'-^^ Prinn and Levis,32 among others, have proposed that the Great Red Spot on Jupiter may be due to red phosphorous formed as a final product of the photodissociation of phosphine. Our interest in the photochemistry of phosphine arises for two reasons: (a) The reports in the literature concerned with the photochemistry of phosphines devote little attention to the analysis of secondary products and quantum yield measurements. Some data for the far-ultraviolet photolysis are available from Melville et al.,4* but no such information has been published for the vacuum ultraviolet photolysis of phosphine. It is worth noting that for "3, which is chemically similar to PH3, secondary processes have been studied extensively.% (b) Formation of a solid film with commercially interesting properties may occur similar to the film formation found in the vacuum ultraviolet photolysis of silicon hydrides3G38and other compounds.39 Hydridic films of silicon have been widely used in photocells and solar cell^.^^^^ The analogous hydridic phosphorous films have not been used for these purposes as yet, although investigations of the properties of hydridic silicon films doped with phosphorous have been condu~ted.~~-~~
Experimental Section The photolyses were carried out in a cylindrical stainless-steel cell that had a diameter of 1.9 cm and an optical length of 13.4 cm. One end of the photolysis cell was fitted with a lithium fluoride window common to a xenon resonance lamp, and the other was coupled via a pinhole leak (diameter of 1 X 10-3-3 X lo9 cm) to a time-of-flight mass spectrometer. The apparatus has been described previo u ~ l y . ~The ~ , xenon ~ ~ resonance lamp, used as a source of 147-nm radiation, was filled with 0.7 torr of xenon and sealed with a greaseless stopcock after prolonged evacuation and degassing on a mercury-free high-vacuum system. (26)S.T. Ridgway, Bull. A m . Astron. Soc., 6,376 (1974). J.,207, (27)S. T.Ridway, . L. Wallace, and G. R. Smith, Astrophys. . . 1002 (1976). (28)R. Beer and F. W. Taylor, Icarus, 40, 189 (1979). (29)F. C. Gillett and W. J. Forrest, Astrophys. J.,187,L37 (1974). (30)J. D. Bergman, D. F. Lester, and D. M. Rank, Astrophys. J.,202, L55 (1975). (31)R. G. Prinn and J. S. Lewis, Bull. Am. Astron. Soc., 7,381 (1975). (32)R. G.Prinn and J. S. Lewis, Science, 190,274 (1975). (33)D. F. Strobel, Astrophys. J.,214,L97 (1977). (34)S. K. Atreya and T. M. Donahue, Reu. Geophys. Space Phys., 17, 388 (1979). (35)H.' 0.Okabe, "Photochemistry of Small Molecules", Wiley, New York, 1978,p 269. (36)G. G. A. Perkins, E. R. Austin, and F. W. Lampe, J. Am. Chem. SOC.,101, 1109 (1979). (37)G. G. A. Perkins and F. W. Lampe, J. Am. Chem. Soc., 102,3764 (1980). (38)P. A. Longeway and F. W. Lampe, J. Photochem., 14,311 (1980). (39)J. R. McNesby and H. Okabe, Adu. Photochem., 3, 157 (1964). (40)D. E. Carlson and C. R. Wronski, Top. Appl. Phys., 36, 287 (1979). (41)H.Dwand, Philos. Trans. R. SOC.London, Ser. A , 295,435 (1980). (42)M.Taniguchi, M. Hirose, and Y. Osaka, J. Cryst. Growth, 45,126 (1978). (43)S. Hasegawa, T.Kasajima, and T. Shimizu, Solid State Commun., 29,13 (1979). (44)N. Sol, D.Kaplan, D. Dieumegard, and D. Dubreuil, J. NonCryst. Solids, 35-36,291 (1980). (45)M.Hirose, M. Taniguchi, T. Nakashita, Y. Osaka, T. Suzuki, S. Hasegawa, and T. Shimizu, J. Non-Cryst. Solids, 35-36, 297 (1980). (46)E. R.Austin and F. W. Lampe, J . Phys. Chem., 80, 2811 (1976).
1858
The Journal of Physical Chemistty, VOI. 85, NO. 13, 1981
Blazejowski and Lampe
With the above-described construction of the lamp, light However, when the identical electronic structures of both intensities in the range of 0.6 X 1015-10 X 1015 quanta/s compounds are taken into account, similar extinction have been obtained. coefficients are expected, an expectation observed for other The light intensity incident on the reactant mixture was corn pound^.^^^^^ Absorption of the radiation was essendetermined by carrying out the photolysis of hexafluorotially complete at a phosphine partial pressure of 0.08 torr. acetone diluted with He, Ne, or Ar.47 Recorded traces of The photolyses were carried out with PH, (or PDJ a t the current at m/q 119 (C2F5' from C2F6) as a function of partial pressures of 0.08-0.48 torr with He, Ne, and Ar used time were used to determine the initial slope (dillg/dt)o. as diluting gases so that the total pressure in the photolysis The proportionality constant, Pl19, relating ion current at cell was 40 f 0.5 torr. All gas mixtures were prepared by m/q 119 to the pressure (concentration) was measured by using a Saunders-Taylor a p p a r a t ~ s . ~ , using samples of pure CzF6 diluted with rare gases. All Diphosphine was prepared by the neutral hydrolysis of measurements were carried out a t a partial pressure of calcium phosphide (Alfa Products) in a modification of the (CFJZCO = 4 torr, and the value @(CzF6)= 1.12 (ref 47) method of Evers and Street." The hydrolysis apparatus& was used to calculate the light intensity. The photodewas attached to a vacuum system, and the preparation was composition of PH, (PD,) results in a deposition of solid done in a slow flow of helium gas. The reaction products, film on the window of the lamp which reduces the light PH3, PzH4, and unreacted HzO, were passed through a intensity incident on the reactant mixture (Figure 4). This series of traps (numbered 1-3) and a KOH drying tube. necessitated a cleaning of the window, usually after a few The HzO condensed in trap 1 and in the drying tube, both photolyses of phosphine, as well as a determination of at 293 K. Relatively pure PzH4 was collected in trap 2 at 195 K (acetone slush bath), and PH, with traces of P2H4 incident light intensity prior to each quantum yield meain trap 3 a t 77 K (liquid nitrogen). The crude product surement. Reaction products were identified by comparison of the (P2H4)was evacuated many hours at 195 K and stored at overall mass spectrum produced by the photolysis with the 77 K in the dark. When mixtures with rare gases were individual spectra of Hz, HD, Dz, PzH4,48-50and PzD4.48 prepared, diphosphine was evaporated from a reservoir The quantum yields for the loss of reactants were deterwhich was kept a t 273 K. Deuterated phosphine and diphosphine were prepared mined from replicate measurements of the initial rates of in the same manner except for the substitution of 99.8% depletion of PH3 using the PH3+ (m/q 34) current or PD, deuterium oxide, obtained from Alfa Products. PzD4 was using the PD3+ (m/q 37) current. The parent ions (m/q purified as above. The crude PD, was purified by repeated 34 and 37) of the substrates were monitored because no s ~ ~ ~ ~ freeze-pumpthaw cycles at 142 K (n-pentane slush bath) corrections due to interferences from the p r o d ~ c t were until a reasonably pure sample was obtained. necessary. On the other hand, corrections due to impurDiphosphine is a colorless compound with a melting ities in PD, were necessary. p 0 i n t ~ 9of~174 ~ K and a boiling point" of -336 K. Heat, The quantum yields for the growth of products were light, and contact with impurities of various sorts (mercury, determined in the same manner, but experimentally degrease) cause slow decomp~sition."~~~ Therefore, it was termined values of Ai/At were used instead of the initial difficult to prepare mixtures of the pure compound in the slopes. The time of irradiation, At, was chosen so that the rare gases. Using the m q 34 ion current at 50 eV, we degree of depletion of substrates was less than 0.03 and estimate amounts of PH, d 5 7 to have always been less than the concentrations of products in the linear-growth region 10%. This estimate is supported by mass spectra obtained was sufficient to measure respective ion currents, Ai. This at low ionizing energy, Le., 11 eV. photolysis time was within the range of 6-12 s. The calThe amounts of impurities of the deuterio compounds ibration constants p2 and p4,which relate currents at m/q were estimated from their mass spectra at low ionizing 2 and m f q 4 to the concentrations of Hz and D2, respecenergy, i.e., 11 eV. Thus the sample of PD3 contained tively, were determined as above, using the pure comPHzD (7.5%), PHDz (1.4%),and PH, (1.0%) as impurities. pounds diluted with the rare gases. When the simultaP2D4contained impurities of two sorts, namely, PH,D3-, neous determination of the quantum yields of H2, HD, and ( n = 0, 1, 2, 3) and also PzH,D4-, ( n = 1,2, 3,4), with the D2 was of interest, P3 for HD was taken as the mean of P2 total perhaps up to 40%. and p4. He (99.995%), Ne (99.995%), Ar (99.998%), Hz In the case of diphosphines, it was not feasible to (99.95%), PH, (99.999%), n-butane (99.98%), and measure the calibration constants &(P&) and P70(PZD4) ethylene (99.98%), all from Matheson, and Dz (99.5%, in the same direct manner because of the thermal decomLinde), hexafluoroethane (PCR), and hexafluoroacetone position of these compounds. A satisfactory technique was (Du Pont) were used as received. Nitric oxide (99.0%), to measure the calibration constants for P2H4 and PzD4 from the Matheson Co., was subjected to a freeze-pumprelative to P34from PH,. In this way, phosphine instead thaw cycle in which the volatile material first appearing of the unstable diphosphines could be used for calibration during a slow warm-up period was used. purposes. Also in this case, some corrections due to the variable amounts of PH3 and PD3 in the P2H4 and PzD4 Results were necessary. Quantum Yields. Examination of the overall mass The vacuum ultraviolet absorption spectrum of PH3 has spectra of the contents of the photolysis cell during and been reported by DiStefano and co-workers,lgwho found after photolysis indicates that the gas-phase products of the absorption coefficient at 147 nm to be -1.9 X lo4 dm3 the decomposition of PH, at 147 nm are H2 and PzH4. The mol-' cm-'. For PD, only qualitative data are a ~ a i l a b l e . ~ ~ relative abundances of ions from PzH4, formed upon photolysis of PH,, are the same as in the mass spectrum (47) G. G. A. Perkins, E. R. Austin, and F. W. Lampe, J. Chem. Phys., 68, 4357 (1978). (48) Y. Wada and R. W. Kiser, Znorg. Chem., 3, 174 (1964). (49) T. P. Fehlner, J. Am. Chem. SOC.,90, 6062 (1968). (50) T . P. Fehlner and R. B. Callen, Adu. Chem. Ser., No.72, 181-90 (1968). (51) C. M. Humphries, A. D. Walsh, and P. A. Warsop, Discuss.Furaday SOC.,35, 148 (1963).
(52) L. C. Glasgow and P. Potzinger, J. Phys. Chem., 76, 138 (1972). (53) K. W. Saunders and H. A. Taylor, J. Chem. Phys., 9,616 (1941). (54) E. C. Evers and E. H. Street, J . Am. Chem. SOC.,78,5726 (1956). (55) R. C. Marriott, J. D. Odom, and C. T. Sears, Inorg. Synth., 14, l(1973). (56) E. R. Nixon, J . Phys. Chem., 60, 1054 (1956). (57) T. P. Fehlner, J . Am. Chem. SOC.,89, 6477 (1967).
The Journal of Physlcal Chemistty, Vol. 85, No. 13, 1987
147-nm Photolysis of Phosphine and Phosphine-d,
1859
TABLE I: Quantum Yields in t h e Photolysis of Phosphine" intensity, quanta/s 1.4x 10'5
3.5 x 1015
a
P(PH,), torr 0.08 0.16 0.32 0.40 0.48 0.08 0.16 0.24 0.32 0.40 0.48
@(-pH,) 2.0 2.9 4.0 4.9 4.7 1.2 1.8 2.3 3.1
@(P*H,) 0.18 0.39 0.60 0.74 0.71 0.10 0.22 0.18 0.34
3.4
0.54
@(H2) 2.4 4.1 4.9 0.93 1.7 2.7 3.1 3.5 3.8
2@(P,H,)/ @(-pH,) 0.18 0.27 0.30 0.30 0.30 0.17 0.24 0.17 0.22 0.32
2@(H2 (- PH,)
@
1.7 2.0 2.0 1.6 1.9 2.3 2.0
2.2
Helium used as diluent gas. Total pressure was 40 torr in all experiments.
TABLE 11: Quantum Yields in the Photolysis of Phosphine-d," P(PD,), 2@(P2D4)/ 2@(D,)/ torr @(-PD,) @(P2D,) @ ( D , ) @(-PD,) @(-PD,) 0.16 0.32 0.48
1.2 1.7 1.9
0.040 0.10 0.10
0.93 1.6 2.3
0.067 0.12 0.11
1.6 1.9 2.4 a Neon used as a diluent gas. Total pressure was 40 torr in all experiments. Light intensity was 3.5 x quanta/ S.
l-!l!l
Light Ti me On Light O f f
Flgure 1. Depletion of PH, ( m l q 3 4 )and formation of H2 ( m l q 2 ) and P,H, ( m l q 6 6 ) 6 4 ) in the photolysis of PH,. Partial pressure of PH,
= 0.48 torr.
of a synthetic sample of prepared diphosphine. This fact indicates the absence of P2 in the gas phase. It was also supported by analyzing the increase of the ion currents of P2H4+ and P2+as functions of photolysis time. The mass spectra of the photolyte exclude the presence of P4 and any phosphorous hydrides of higher mass than P2H4 in the gas phase. The ion currents of PH3+ (i34 = [PH,]), H2+ (i2 0: [H,]), and P2H4+ (iM a: [PzH4])are presented in Figure 1 as functions of photolysis time. The shapes of the curves indicate that both products are formed simultaneously with decomposition of phosphine. The photolysis curves for the depletion of phosphine and for the increase of hydrogen are almost mirror images, a fact which indicates that molecular hydrogen is formed simultaneously with the decomposition of phosphine. However, it may be seen that the shape of the curve for P2H4 formation is slightly different from that of H2 The rates of formation of both products are the same in the first few seconds of photolysis, but the steady-state concentration of P2H4 is attained significantly sooner. Moreover, the concentration of PzH4begins to fall slightly before the irradiation is stopped. It is worth noting that the formation of diphosphine in the photodecomposition of phosphine has only very recently been reported. Ferris and B e n ~ o showed n ~ ~ that (58)J. P.Ferris and R. Benson, Nature (London),285, 156 (1980).
diphosphine is an unstable product in the 206-nm photolysis of phosphine. Our results demonstrate clearly that diphosphine is also an unstable product of phosphine photodecomposition at 147 nm. Quantum yields for the depletion of substrates and for the formation of the volatile products are shown in Tables I and 11. It may be seen that all quantum yields increase with an increase of the partial pressure of substrate. The pattern of changes of @(-PH3)with substrate pressure is similar to that reported in the Hg-photosensitized photolysis of PH3,6and it is worth noting that analogous pressure dependencies of the quantum yields have been reported in the vacuum ultraviolet photolyses of a number of other corn pound^,^^ e.g., (CF3)2C0,47SiH4,36and Si2H6.37The values of the quantum yields were determined at various stages of the film deposition on the window of the lamp, and at various ages of the lamp. As a result, the incident light intensities were varied within a factor of 10 from that characteristic of a freshly filled lamp with a clean window. As may be seen in Table I, all quantum yields decrease with increasing light intensity. The quantum yields are independent of the amount of deposit on the window and the walls of the reaction vessel. Also, as seen in Tables I and 11, the quantum yields in the photodecomposition of PD3 are smaller than the corresponding values in the case of PH3 Moreover, the dependencies of the quantum yields on pressure and light intensity are not as strong for PD3 as for PH3. The last two columns of Tables I and I1 indicate the material balances obtained by consideration of only gaseous products. The amount of phosphorous in the reacted phosphine that is accounted for by diphosphine increases with increasing partial pressure of phosphine to a plateau of -30% in the case of PH3 and 12% in the case of PD3. Thus the major fraction of the phosphorous reacted is contained in the solid deposit on the windows and the walls. The last column in Tables I and I1 shows that @(HJ and @(D2)are in excess of the values characteristic of PzH4 being the only phosphorous-containing product. The values of 2@(Hz)/@(-PH3)and 2@(D2)/@(-PD,) are consistent with the principal reaction being conversion of
-
1880
The Journal of Physical Chemistry, Vol. 85,
No. 13,
1981
Blazejowski and Lampe I .o
P>._
0
1
I
30
60
I
I
120
I
I
I
180
Time of PH, Photolysis
I
240
I
0.7 O.*I
\
1
300
(SI
Flgure 2. Reduction of incident light intensify by the formation of the deposit on the window of the photolysis cell: (A) pRls = 0.48 torr; (0) ppHs= 0.32 torr; (0) ppHs= 0.16 torr.
phosphine to a solid phosphorous hydride, (PH),, phosphorous, and molecular hydrogen. Solid substances formed on the walls of the photolysis cell and on the window of the lamp may be seen directly as a white or light yellow deposit. This deposit, on the window of the lamp, causes a decrease in the flux of the incident radiation, as may be seen in Figure 2. The amount of the deposit increases with time of irradiation, and the rate of buildup of the deposit increases with an increase in the partial pressure of phosphine. The pressure effect in the formation of the deposit probably arises from differences in the optical lengths for absorption of the radiation. A t higher pressures of the substrate, radiation is absorbed in thin layers close to the window, and the solid deposit is formed mostly on it. At lower pressures of PH3, radiation is absorbed in the entire volume of the photolysis cell and the deposit is formed uniformly on the walls. The composition and the structure of the solid deposits have not been studied. However, on the basis of material balances, we conclude that the deposits are mixtures of higher phosphorous hydrides and phosphorous. The material balances with respect to the gaseous products for all experiments carried out show that the ratio of hydrogen to phosphorous in the solid formed ranges initially from 1.3 for photolyses a t the lowest partial pressure of phosphine to 0.6 for photolyses at the highest partial pressure of phosphine. The presence of phosphorous in the deposit has been supported by performing Hg-photosensitized photolyses of H2 or D2 in a cell whose walls were previously covered with the solid products of the 147-nm photolysis of PH3. Under these conditions only PH3 or PD3 was found in the gas phase. It is difficult to predict the behavior of solid phosphorous hydrides in the presence of H or D atoms. However, solid phosphorous seems to be the only possible precursor for PD3 in reaction of the deposit from PH3 with D atoms. The reactions of other forms of phosphorous with hydrogen atoms have been well described.*~~~ Effect of Monoradical Scavengers. In the formation of diphosphine, two pathways might be expected: (a) combination of PH2 radicals and (b) insertion of P H into a PH3 molecule. Sometimes it is possible to distinguish these pathways if the photolyses are performed in the presence of scavengers of monovalent radicals, i.e., NO, 02,CH2= CH2. For example, it is well-known that monovalent carbon,%silicon,s38 and even NH260radicals are effectively
Figure 3. Dependence of the fractional quantum yields of hydrogen formation on the composition of reactants in the photoiyses of PH3-PD, mixtures: (0)@(H2); (A) @(D2); (0) @(HD).
intercepted by nitric oxide. Accordingly, we have examined the effect of nitric oxide on the photolysis. Although no information about the reactivity of NO toward PH2 radicals is available, it is known that NO does not react with phosphine.61 The mass spectra recorded during photolyses of PH3NO mixtures a t 147 nm were quite different from those observed in the photolysis of pure phosphine. Two new products were found, namely, N20 and probably PH2N0. The latter was identified from the observation of a new peak, m / q 61 (PNO'), along with an increase of relative intensities of ions m / q 62 (PHNO+ and Pz+)and m / q 63 (PHZNO' and P2H+)as compared with the relative intensities of these ions in the mass spectrum of pure diphosphine. The quantum yield for formation of P2H, is reduced by the presence of NO, but there is also an increase of @(-PH3). Although this complicates the monoradical scavenging mechanism and precludes drawing firm conclusions, it is noteworthy that this behavior in the presence of NO is completely analogous to the photochemical behavior of SiH4 in the presence of NO.36 Ethylene, in such concentration that its absorption was negligible in comparison with the absorption of phosphine, did not affect the course of photolysis of PH,. Also, no effect on the photolysis was observed when H2 or D2 was added. Photolysis of PH3-PD3 Mixtures. In an attempt to obtain further mechanistic insight, we have examined the isotopic distribution in the gaseous products of the photolysis of PH3-PD3 mixtures. The dependence of the fractional quantum yields of hydrogen formation, Le., @J(@(H2)+ NHD) + ND2)),is shown as a function of reactant composition in Figure 3, the points being the experimental data and the lines being calculated from a mechanism of hydrogen formation to be discussed subsequently. It is clear from the experimental data that the yields of H2 and D2 are significantly higher (by a factor of -2) than would be the case if hydrogen was produced solely from reaction 1. This indicates that a major primary H + PH3- H2 + PH2 (1) process must be the formation of molecular hydrogen. Combining this fact with the spectroscopic observation of electronically excited P H radicals leads to the conclusion that a major primary process must be reaction 2. PH3 + hu PH* + Hz (2) +
(59) M. Halmann,Top. Phosphorous Chem., 49 (1967). (60) H. 0. Okabe, "Photochemistry of Small Molecules", Wiley, New York, 1978, p 262.
(61) M. Halmann and L. Kugel, J. Chern. SOC.A, 3272 (1962).
The Journal of Physical Chemistry, Vol. 85,No. 13, 1981 1881
147-nm Photolysis of Phosphine and Phosphine-d,
eq 5, in which [P2H4I0is the concentration of diphosphine
(X/[PzH4])e-xt= h/[P2H,IO + k ( l
-
e-M)
(5)
0I
B ‘Y)
1 081 00
I
I
1
02
01
03
I
(I-e-A’I
Flgure 4. Second-order kinetic plot relative to the thermal decomposition of phosphine.
at the instant the light is turned off. A plot of the left-hand side of eq 5 vs. (1-e-xt), shown in Figure 4, yields a very satisfactory straight line indicating the second-order nature of the diphosphine decomposition. From the slope of the line in Figure 4, we obtain a second-order rate constant of It = (4.25 f 0.18) X lo-’* cm3/(molecule s). In most of the photolysis experiments, a much larger leak, having a leak rate constant of 1.13 X s-l was used. The measured value of the second-order rate constant for diphosphine decomposition permits us to conclude that thermal decomposition of diphosphine cannot explain the much lower quantum yields of its formation relative to those for the disappearance of phosphine. The thermal decomposition probably is a contributing cause of the slightly different time dependencies for hydrogen formation and diphosphine formation seen in Figure l.
Discussion The isotopic distribution in the diphosphine formed was Nature of the Primary Processes. Theoretical considexamined mass spectrometrically at low ionizing energy erations& of the vacuum ultraviolet absorption bands of so as to minimize fragment ion formation. Although the phosphine around 147 nm suggest that Rydberg-type accuracy was not sufficient to draw quantitative conclutransitions are involved. Combination of this suggestion sions over the entire range of masses corresponding to with the data of DiStefano et al.l!+zl leads to the conclusion P2HnD4-,(n = 0, 1,2, 3,4), large amounts of PzHzD2were that absorption of 147-nm radiation is due principally to formed at all reactant compositions. Since the insertion the processes mechanism of either P H or PD into PH3 and PD3 can never produce P2H2D2,we must conclude that the major PH3(g1A1’) + hu PH3(C1A1’) (6) source of diphosphine is the combination of PH2 radicals as shown in reaction 3, a reaction that probably requires PH3(Z1A1’) + hu PH,(fPA,”) (7) a third body. with the photodecomposition being a result of the reactions PH2 PH2 M P2H4 M (3) of the products of reactions 6 and 7. The Rydberg-type transitions are spin-allowed, and so the absorption coefDecomposition of Diphosphine. It has been mentioned ficient at 147 nm is quite large. Since the spectrum of earlier that diphosphine accounts for at most 30% of the ,~~ phosphine at 147 nm is diffuse or c o n t i n u o u ~transitions phosphorous from the reacted phosphine. This raises the 6 and 7 probably do not comprise all of the possibilities. question as to whether this low yield of diphosphine is It is difficult to predict with any degree of certainty the characteristic of the photochemistry of phosphine or decomposition pathways of the excited phosphine molewhether it is an artifact due to the decomposition of dicules. Spectroscopic studies already mentioned indicate phosphine. The thermal decomposition of diphosphine ~ ~most ~ ~ ex~ ~ ~ ~that ~ ~PH, ~ ~PH2, ~ H2, and H are products of the primary has been reported p r e v i o ~ s l y .The decompositions. Energetic considerations suggest that H tensive work on diphosphine decomposition is that of and H2 should be in their ground electronic states but that Fehlner,57who reported the reaction to be of zero kinetic P H and PH2 are formed in excited electronic states. All order in the temperature range of 570-650 K with an acfragments may carry excess vibrational, rotational, and tivation energy of 92.8 kJ/mol. translational energy following dissociation. Inclusion of We have examined the time dependence of the thermal spin and orbital symmetry conservation r ~ l e s ~and ~ , ~ ~ * ~ disappearance of diphosphine at room temperature subenergetics leads to the following primary dissociations of sequent to its formation by the 147-nm photolysis of PH3 phosphine molecules excited by absorption of 147-nm rain our mass-spectrometric flow system. After formation diation: of P2H4 by the photolysis, the light is turned off, and the rate of loss of PzH4subsequent to this time (as indicated PH(CIAl’) PH2(A2A1)+ H(Q) (8) by the intensity of the ion with m l q 66) can be written as r ~ ~ rate constant of in eq 4, where X is the f i r ~ t - o r d e leak PH(b’Z+) + Hz(ZIZg+) (9) -d[P,H,]/dt = X[PZH4] + k[PzHJ” (4) PH(b’l;+) + 2HPS) (10)
+
+
-
--
+
-
- -
the apparatus and n is the reaction order. In order to obtain decomposition rates comparable to the leakage into the ion source, a very small pinhole with a leak rate constant of 4.74 X s-l was used. The best fit to the experimental data is for n = 2; i.e., the decomposition of diphosphine is second order, as may be seen in Figure 4. Integration of eq 4 with n = 2 yields
For kinetic and mechanistic purposes it is convenient to consider the detailed processes 6-12 to be represented by the three primary processes 13-15, where the 4’s rep-
(62) T. P. FehlnerJ. Am. Chem. SOC.,88, 1819 (1966). (63) T. P. Fehlner, J. Am. Chem. SOC.,88, 2613 (1966). (64) T. P. Fehlner, J. Am. Chem. SOC., 90, 4817 (1968). (65) R. B. Callen and T. P. Fehlner, J. Am. Chem. SOC., 91, 4122 (1969).
(66) Y. Hatano, Chem. Phys. Lett., 56, 314 (1978). (67) H. 0. Okabe, “Photochemistry of Small Molecules”, Wilev. _ .New York, 1978, p 71. (68) M. N. R. Ashford, M. T. Macpherson, and J. P. Simons, Top. Curr. Chem., 86, 1 (1979).
PH3(O1A2/’)
-
PH2(%2Bl)+ H(%)
PH(clII) + Hz(X’Zg+)
(11)
(12)
1862
Blazejowski and Lampe
The Journal of Physical Chemistry, Voi. 85, No. 13, 1981
resent primary quantum yields. PH3 + hv
-.% PH* + H2
h + hv+PH2* +H PH3 + hv -% PH + 2H
PH3
(13) (14)
(15) Secondary Reactions. As seen in Table I, quantum yields for the disappearance of phosphine depend on the light intensity and the pressure and attain values in excess of 4. If one assumes the usual reactions of free radicals with neutral molecules in the gas phase, primary processes 13 and 14 can account for at most three and two molecules per quantum destroyed, respectively. Yet reactions 13 and 14 must be occurring, according to spectroscopic evidence; moreover, the results of the photolysis of mixtures of PH3 and PD3 indicate that reaction 13 is a major process. In order to obtain quantum yields for phosphine destruction above 4, with inclusion of all three primary processes, and to account for the light-intensity dependence, we suggest that the photodecomposition involves a short chain reaction. After consideration of a large number of possible mechanisms subsequent to reactions 13-15, we propose that shown by eq 16-24 as representing the most satisPH* + PH3+ PH PH2 + H (16) (17) PH* PH3 PH + PH3 (18) H PH3 H2 + PH2 (19) PH2* PH3 PH3 PH2 PH hv (20) PH* (21) PH2* PH2 + hv
+
+ + +
-+
+
+
+
+
-
+
+
PH
+ PH
Wall
-
P ~ ( s+ ) Hz
(22)
Wall
PH(s) + H PH2 (23) P2H4 + M (24) PH2 + PH2 + M factory description of the 147-nm photolysis of phosphine at relatively high partial pressures of PH3 (i.e., >0.2 torr). This mechanism is valid only a t relatively high partial pressures of PH3 because we have neglected the reactions of H atoms with PH2 radicals and with each other. Such reactions will become important at low partial pressures of PH3 and will compete effectively with reaction 18. Efficient collisional quenching of emission from PH* by PH3 has been demonstrated.18~21~22 Since the radiation energy emitted, namely, 83 kcal/mol, is in excess of the average P-H bond energy in PH3,19 we assume that quenching may be also accompanied by dissociation and write eq 16 and 17 to describe these processes. On the other hand, collisional quenching of PH2* cannot supply enough energy to dissociate PH3.19 However, degradation of the excitation energy in PH2* can occur by the very probable atom transfer reaction, as written in eq 19. that under Reaction 18 has been found to be so fast69*70 our conditions other reactions of H atoms cannot compete with it. Reactions 20 and 21 simply describe the fluorescence from PH* and PH2*. Energetic considerations using average bond energies and known thermochemical information'l indicate that the only energetically
feasible reaction of PH with PH3 is insertion to form P2H4. However, our experiments in PHy-PD3 mixtures show that the formation of P2H4 occurs mainly by combination of PH2 radicals and not by insertion. Moreover, insertion could only arise with singlet PH, while most spectroscopic studies have shown readily the emission from triplet PH,15917-19P but only recently has the observation of excited singlet PH been reported.20*21 Therefore, we conclude that PH radicals (at least triplet PH) do not react with PH3 in the gas phase. Most of the phosphorous lost from the gas phase during the reaction must appear in the solid film produced, since only P2H4 is observed in the gas phase and the yield is too low to account for all of the phosphorous reacted. Therefore, reactions 22 and 23 are proposed to account for this fact. In addition, since H atoms react only by reaction 18, reaction 23 is one of the propagation steps, reaction 18 being the other, for the necessary chain-reaction component of PH3 disappearance and H2 formation. Finally, the formation of diphosphine via coupling of PH2 radicals, in agreement with our studies in the PH3-PD3 mixtures, is written as reaction 24.
Formation of Hz, HD, and Dz i n PH3-PD3 Mixtures. Primary Quantum Yields. The predominant formation of H2 and Dz, relative to HD, in photolyzed PH3-PD3 mixtures indicates that primary process 13 must play a very important role. We may make this conclusion somewhat more quantitative on the basis of the mechanism discussed above. A full kinetic treatment of hydrogen formation in an irradiated PH3-PD, mixture using the complete mechanism of eq 13-24 leads to very cumbersome and intractable expressions. If, however, we neglect the heterogeneous reactions 22 and 23, we can get approximate relationships for the relative quantum yields of H2, HD, and D2 which are valid within the accuracy of other assumptions that are made. A standard, steady-state kinetic treatment of the PH3-PD3 system, neglecting eq 22 and 23, leads to eq 25-27, where y is the ratio [PH3]/([PH3]
+
(69) J. H. Lee, J. V. Michael, W. A. Payne, D. A. Whytock, and L. J. Stief, J. Chern. Phys., 65, 3280 (1976). (70) J. H. Lee, J. V. Michael, W. A. Payne, D. A. Whytock, and L. J. Stief, NBS Spec. Publ. ( U S . ) , 526, 345 (1978). (71) H. M. Rosenstock, K. Draxl, B. W. Shiner, and J. T. I*erron, J. Phys. Chem. Ref. Data, 6,Suppl. No. 1 (1977).
1
@(HD)=
+ [PD,]) of the reactants; kD/kH is the ratio of rate constants for D and H atom abstraction from PD3 and PH3, respectively, and is taken as 0.3 by analogy with other
-
The Journal of Physical Chemistry, Vol. 85, No. 73, 7987
147-nm Photolysis of Phosphine and Phosphine-d3
TABLE 111: Primary Quantum Yields in the 147-nm
I
I
I
Photolysis of PH, and PD, process ~
1863
@
PH, t h u + P H * + H, PH, t hv -+ PH,* + H PH, t hu -+ PH + 2 H PD, + hu + P D * + D, PD, + hv + P D , * + D PD, + hu ’PD + 2 D
0
0.8 0
0
similar systems;72uD/uH is the ratio of quenching cross sections (i.e,, reactions 16 and 17) for PD, and PH3, respectively, and is assumed, by analogy with Hg(3P1) quenching,73to be 1/3; and 4 b H are the quantum yields of primary processes a and b, i.e., reactions 13 and 14, respectively, for PH3 molecules, and 4 a and 4 b D are the same primary processes for PD, molecules; C is the total concentration of phosphine, i.e., [PH,] + [PD,] = 1.55 X 10l6molecules/cm3; kB/k16 is estimated from the measured luminescence lifetime of PH* and quenching cross sectionz to be 4.4 X 1015molecules/cm3; and all other terms are as discussed previously. With these estimated numerical values, eq 25-27 may be used to calculate relative values of the quantum yields of Hz, HD, and Dz (for a first choice of the primary , c$bH, 4 b D ) as functions of the quantum yields c$d-$a, reactant ratio y. The values of the primary quantum yields and other parameters were then adjusted to give the best fit to the experimental data, the results of which are shown as the solid line in Figure 3. The assumption was made that $Jd + 4 b H + 4 c =~4a @bD @,.D = 1. In this Way, the following values of parameters have been found: k D / k H = 0.3; a D / q + = 0.1; and k a / k 1 6 = 2.5 x ioi5molecules/cm3. The fit is quite good, as may be seen in Figure 3, and it is from this procedure that we have derived the primary quantum yields shown in Table 111. Kinetic Treatment of the Mechanism. A standard, steady-state kinetic treatment of the mechanism depicted by eq 13-24 leadds to the following expressions for the quantum yields for PH3 depletion, H2formation, and P2H4 formation: 9(-PH3) = 3 - 24, - 4 b
+
B
i
-~
‘(P2H,)
Y
h
A
,
A
A
A
I
I
Partial Pressure of PH,
i n Torr
Flgure 5. Dependence of quantum yields on partial pressure of PH, in the photolysis of phosphine. Light intensity = 3.5 X loi5 photons s-’. (0) @(-PH3); (0) iP(H2); (A) W&J. I
I
I
I
I
I
I
I
J
+
+
2dak16[PH31 ki6[PH31 + h7[PH31 -F kzo
0
8
0.1 0.1 0.35 0.4 0.25
+
(&)
112
4i
0
It 0 0
I I
I 2
I
I
3
I 6
I 5
4
I
I 8
7
1
IO
9
L i g h t I n t e n s i t y ( p h o t o n s s - ’ ) a IO-’’
Flgure 6. Dependence of quantum yields for depletion of phosphine on the light intensity. ppH)= 0.48 torr.
the derived quantum yields as functions of pressure in Figure 5. The values giving the best fit to the data are k171k16= 1.1, kpo/k16 = 4.4 x ioi5 molecules/cm3 and k 2 3 /(kZ,[M]) = 1.6 X l O I 4 molecules/(cm3 s). As may be seen in Figure 5, the quantum yields derived from the mechanism are in reasonable accord with the experimental results at partial pressures of PH3 above 0.2 torr. The mechanism fails, however, at lower pressures, and we believe that this failure is due to the occurrence of other reaction channels for H atoms. Thus at the lower pressures reactions 31-3374975compete with reaction 18 with H PHZ P H + Hz (31)
+
H
-+
+ PHp + M PH3 + M H + H + M -Hz + M
(32)
+
(33)
In eq 28 and 29, q is the rate of absorption of quanta per unit volume. Using the values of the primary quantum yields in Table 111, and choosing values of k17/k16, kzo/k16, and kZ:/(kp4[MI) to give the best overall fit to the experimental data at PH3 partial pressures above 0.2 torr, we have plotted
the net result of depressing all of the quantum yields. In the true limit of zero partial pressure of PH3, all fragments from primary processes will go to the walls and 9(-PH3) 1, @(HA a, = 0.8, and a(P2H4) 0. These limits appear to be approximately satisfied by the experimental data in Figure 5. The experimental and derived dependence of 9(-PH3) on light intensity, for the higher partial pressure of PH,
(72)E.R.Austin and F. W. Lampe, J. Phys. Chem., 81,1134(1977). (73)J. G.Calvert and J. N. Pith, “Photochemistry”,Wiley, New York, 1966,p 74.
(74)D.W. Trainor, D. 0. Ham, and F. Kaufman, J. Chem. Phvs.. 68. 4599 (1973). (75)A.J. Stace and J. N. Murrell, Int. J. Chem. Kinet., 10,197(1978).
+
-
-
~
~~
~
~~~
~
~~
1864
J. Phys. Chem. 1981, 85, 1864-1871
studied, is shown in Figure 6; the solid line is from eq 28, using the values of k17/k16, kzo/k16) and k??/(kz4[M]) mentioned earlier, and the points are experimental. A On the other hand, eq 30 similar plot is found for @(Hz). and, therefore, the high-pressure mechanism predict no intensity dependence for @(PzH4),but a dependence is observed experimentally (cf. Table I). We do not fully understand this discrepancy, but a possible explanation might be that photodecomposition of PzH4 is influencing our measurement of its initial rate of formation. This influence, which would be to reduce the quantum yield, would become increasingly stronger as the light intensity is increased.
The complete mechanism is clearly very complicated, and that shown for the high-pressure situation by eq 13-24 is undoubtedly oversimplified. Nevertheless, the agreement obtained between the experimental quantum yields and those derived from the mechanism of eq 13-24, including their dependencies on pressure and intensity, suggests that the proposed mechanism is a good approximation that forms a useful framework in which to consider the vacuum ultraviolet photodecomposition of phosphine. Acknowledgment. This work was supported by the US. Department of Energy under Contract No. DE-ASOB76ER03416.
Solute Liquid-Gas Activity and Partition Coefficients with Mixtures of n-Hexadecane and n-Octadecane with N,N-Dibutyl-2-ethylhexylamide Solvents C.-F. Chlen, M. M. Kopecni,+R. J. Laub,’ and C. A. Smith Department of Cbmistry, The Ohio State University, Columbus, Ohlo 432 10 (Received: January 13, 198 1)
GLC-based activity ( y i ) and partition (KRm)coefficients are reported for aliphatic, alicyclic, chlorinated aliphatic, aromatic, and heterocyclic solutes (A) at infinite dilution with blends of n-hexadecane and n-octadecane solvents (B)with N,N-dibutyl-2-ethylhexylamideadditive (C) over the volume fraction range 4c = 0-1 at 20-50 “C. Comparison of pure-solvent activity coefficients for n-hexane, n-heptane, and benzene of this study with those of others establishes a level of agreement of fl-2%. Plots of blended-solvent partition coefficient against additive volume fraction are in every instance found to be curved positively, although the degree of curvature for three of the four chlorinated aliphatic solutes is slight. Theoretical expressions conforming to conventional models of solutions are employed to fit a quadratic function to f l %to the data for all solutes except dichloromethane, chloroform, and 1,2-dichloroethane for which convergence could not be obtained. Solute-solvent and additivwolvent interaction parameters are derived from the fitted functions; those of the latter found with n-hexane, n-heptane, and cyclohexane are, as expected, approximately solute independent. The resultant averaged values are employed to deduce presumed hydrogen-bonding complexation constants KAC for the three chlorinated hydrocarbons with the amide additive, but which in every in$tance are found to be negative. A previously reported model of solutions which predicts linearity of plots of KR(M)against 4~ is alternatively examined from the standpoint of additive self-association. Hypothesis of a dimerization constant Kd of 0.20 dm3mol-’ and of KAc of 0.05 dm3 mol-’ enable the experimental data of the chlorinated solutes to be fitted to f1.5%; when KAC is set to zero, the model also describes the (nonlinear) alkane, alicyclic, and aromatic solute data with the same degree of accuracy. Failure of the conventional model cannot in the present instance be reconciled, however, with the success of the extended form of the alternative presented; it is therefore suggested that, in view of the importance of mixed-solvent systems, the situation warrants further and comprehensive study.
The various forms of relevant eq~ationsl-~ derived in the course of spectroscopic and chromatographic study of weak intermolecular complexation have been shown rigorously3 to comprise only one or another alternatives of the simple relation formulated initially by Purnell and Vargas de Andrade4J and later expanded6 and clarified’ by Laub and Purnell:
KR(M) = ~ B ~ R (+ B )~cKR(c)
(1)
where K‘,,,, is the solute (A) partition coefficient with mixed solvents B and C (M = B + C), @J represents a volume fraction, and K&i) (i = B or C) is the solute partition coefficient with the respective pure phase. Albeit demonstrated experimentally to apply to several hundreds of systems, eq 1has nonetheless been criticized consistently on the basis that it cannot be derived from models of ‘Boris Kidric Institute of Nuclear Sciences-VINCA, Chemical Dynamics Laboratory, P.O. Box 522, Beograd 11001 Yugoslavia.
solutions which, broadly speaking, are considered to be more conventional and, hence, more generally “realistic”! While eq 1 has in more recent work been shown9 to be indistinguishable from contemporary descriptions1@l2of (1) R. J. Laub and R. L. Pecsok, J . Chromatogr., 113, 47 (1975). (2) R. J. Laub and R. L. Pecsok, “Physicochemical Applications of Gas Chromatography”, Wiley-Interscience, New York, 1978, Chapter 6. (3) R. J. Laub and C. A. Wellington in “Molecular Association”, Vol. 2, R. Foster, Ed., Academic Press, London, 1979, Chapter 3; R. J. Laub
and J. H. Purnell, unpublished work. (4) J. H. Purnell and J. M. Vargas de Andrade, J. Am. Chem. SOC.,97, 3585 (1975). (5) J. H. Purnell and J. M. Vargas de Andrade, J . Am. Chem. SOC.,97, 3590 (1975). (6) R. J. Laub and J. H. Purnell, J . Am. Chem. Soc., 98, 30 (1976). (7) R. J. Laub and J. H. Purnell, J. Am. Chem. SOC.,98, 35 (1976). (8) C. L. Young, J. Chromatogr. Sci., 8 , 103 (1970). (9) R. J. Laub, D. E. Martire, and J. H. Purnell, J. Chem. SOC.,Faraday Trans. 2, 74, 213 (1978). (10) G. M. Janini, J. W. King, and D. E. Martire, J . Am. Chem. SOC., 96, 5368 (1974). (11) G. M. Janini and D. E. Martire, J . Chem. SOC.,Faraday Trans. 2, 70, 837 (1974).
0022-3654/81/2085-1864$01.25/00 1981 American Chemical Society
