J. fhys. Chem. 1983, 87,1924-1928
1924
plained. Conformations of this type are possible when n = 3 and 4, but not when n = 2. This idea is supported by INDO calculation^^^ for the radical Ph(CH2)3CH2..Three conformations of this radical, drawn by are shown in Figure 7. In these conformations, the aliphatic chain is fully staggered. The proton hyperfine splitting constants predicted by the INDO calculations are shown, except when they are less than 0.1 G. Relative to conformation b, in which the interaction between the unpaired electron and the phenyl group is probably minimal, conformation a is predicted to be more stable, by 54.1 kJ mol-', whereas conformation c is predicted to be less stable, by 37.2 kJ mol-'. It appears likely that the stabilization of the conformation shown in Figure 7a is overestimated by the INDO calculation^.^^ In spite of this, it does seem possible that there may be a small but significant stabilization of this conformation. The lifetimes of the different conformations are evidently too short for splitting due to the S protons or ring protons to be resolved. It may be that the disposition of the reactive groups shown in Figure 7a favors the formation of a transition state on the reaction pathway leading to Tetralin, which is formed as a major product during the decomposition of 5-phenylpentanoyl peroxide in benzene solution at reflux temperature.12 Doyle et a1.%studied the ESR spectra of a homologous series of three free radicals, of which the most comprehensive details were reported for the species 12 and 13.
C H2CH2C H i Ph
12
13
(54) Beppu, Y. QCPE 1979, 10, program 370. (55) It is interesting to note that CNDO calculations overestimate intermolecular interactions when they are mainly of the charge-transfer type: Lochman, R.; Weller, T. Znt. J. Quantum Chem. 1976, 10, 909. (56) Doyle, M. P.; Raynolds, P. W.; Barenta, R. A.; Bade, T. R.; Danen, W. C.; West, C. T.J.Am. Chem. SOC.1973,95, 5988.
For 12 and 13, the p protons appeared inequivalent in the ESR spectra recorded at -140 and -120 "C, respectively. This behavior may be contrasted with that of n-butyl radicals, the ESR spectra of which display line width alternation involving the p protons, but not inequivalent p protons, at similar temperature^.^^ For radical 12, the inequivalence of the protons suggests that rotamers 14 and 15 are preferred. The differences between the ESR
C H; I
14
CHi I
15
spectra of 12 and n-butyl radicals are understandable, because transitions between rotamers 14 and 15 are expected to be less frequent, for steric reasons, than the analogous transitions between rotamers 3 and 5 of n-butyl radicals. A similar explanation cannot convincingly be used to explain the differences between the ESR spectra of 13 and n-butyl radicals. A possible explanation seems to be that radical 13 prefers conformations analogous to the conformation shown in Figure 7a, in which the p protons are strongly inequivalent. Acknowledgment. This work was done while I was with the University of Malaya, Kuala Lumpur, Malaysia. I am indebted to Dr. K. H. Lee for valuable discussions. My thanks are also due to Mr. T. C. Chua, who carried out some of the synthetic procedures. Registry No. HOCH2CH2.,4422-54-2; t-Bu-CH2CHz-, 20199-83-1; t-Bu-CH&H&Hy, 85250-70-0; Ph,C-CH&Hz, 85250-71-1; Me-(CHJ2CH2.,2492-36-6; Me-(CH2),CH2., 2672-01-7; Me-(CH2)4CH2., 2679-29-0; Ph-(CH2)2CH2., 25088-33-9; Ph4421-85-6; n-propyl radical, (CHJ3CH2.,4399-93-3; Ph-(CH2)4CH2., 2143-61-5.
Collisional Relaxation of Iodobenzene Ions Naomi 6. Lev and Robert C. Dunbar' Department of Chemistry, Case Western Reserve University, Clevebnd, Ohio 44 106 (Received: October 10, 1982; In Final Form: December 27, 1982)
Collisional quenching of optically excited iodobenzene molecular ions was studied by analysis of the kinetics of sequential two-photon photodissociation in the ion cyclotron resonance ion trap. When ICR line broadening was used as an independent calibration of ion-neutral collision rates, it was possible to determine the number of collisions required for internal energy quenching, giving values of 2.5 collisions (iodobenzene bath gas), 7 collisions (cyclohexane), and 50 collisions (methane). These values are consistent with complete energy equilibration in the collision complex for iodobenzene bath gas, but much less than complete equilibration for the other two bath gases. A two-laser variation of the experiment in which an infrared laser supplemented the effect of the visible laser suggested that infrared radiation has an effect kinetically similar to visible radiation in this photochemical system.
Introduction The study of two-photon dissociation processes in the ion cyclotron resonance (ICR) spectrometer provides the possibility of studying excitation and relaxation processes of highly vibrationally excited intermediates. It has been 0022-3654/83/2087-1924$01.50/0
shown that the excited iodobenzene cations created by the absorption of one visible photon' or several IR photons2 (1) Lev, N. B.; Dunbar, R. C. Chem. Phys. Lett. 1981, 84, 483.
0 1983 American Chemical Society
Collisional Relaxation of Iodobenzene Ions
have energy relaxation times on the order of hundreds of milliseconds, in the absence of collisions. By adding bath gases and calculating the change in dissociation rate as a function of pressure one can study the rate of collisional quenching of these excited intermediates for various bath gases. In this way, Kim and Dunba? studied the efficiency of a series of bath gases in quenching excited bromobenzene cations. The efficiency of collisions with bath gas molecules was calculated by comparing the quenching rate derived from a two-photon experiment with a calculated collision rate. A wide range of efficiencies was reported, from more than 50 collisions required for methane to only a few for C6H6, C6H5F, and C6D6. Although this experiment provided noteworthy information about both absolute and relative collisional quenching rates for ion-molecule collisions, its quantitative reliability can be improved by taking advantage of ICR lie-broadening information. The totalrate of ion-neutral collisions, derived from theory in the work of Kim and Dunbar: can be measured directly from the collisional broadening of the ICR lines. This technique, which both eliminates the resort to collision-rate theory, and also cancels errors in pressure measurement, was incorporated into a new series of measurements, using iodobenzene ion as the excited ion partner.
Experimental Section The experimental arrangement has been described previously. Experiments were done in the pulsed mode in a trapped cell ICR spectrometer. A small pressure of iodobenzene ((2-6) X torr) was introduced through one inlet and the bath gas through a second inlet. Bath gas pressures in the 10-’-104-torr range were used for the laser excitation-quenching experiments, and pressures in the 10-5-torrrange for the line-broadening studies. Pressures were read from the ion pump gauges. For the laser experiments, ions were created by a 50100-ms electron beam pulse and trapped for 1.5-2.0 s. A Coherent Model 490 dye module with rhodamine 6G dye, pumped by a Coherent CR12 argon ion laser, was used. The laser beam was spread to a diameter of several centimeters to ensure good overlap with the ions in the ICR cell. Power at the cell was 20-100 mW/cm2. Greater intensity led to dissociation of all the ions in the cell. For the line-broadening experiments, a shorter trapping time of 140 ms was used to minimize ion loss due to the high pressures. At the highest pressures, with methane bath gas, a continuous electron beam was used, but detection was still in the pulsed mode (the trapping time of 140 ms was followed by ion detection and then ejection). At lower pressures, ion concentration was kept low by shortening the electron beam pulse, in order to prevent line broadening from space-charge effects. Line shapes were recorded by sweeping the magnetic field through a 250-G range, about 5 amu at the rf frequency used, 98.5 kHz. The line-broadening and laser experiments for a given bath gas were performed either on the same day or on successive days to ensure that experimental conditions would be comparable. Two molecules were used for this study, a “large” one, cyclohexane, and a “small” one, methane. Because the intent was to study nonreactive collisions, molecules were chosen that did not react with the iodobenzene cations: adding either methane or cyclohexane caused little change (2) (a) Honovich,J. P. Ph.D. Thesis, Case Westem Reserve University, 1982. (b) Honovich, J. P.; Dunbar, R. C. J.Am. Chem. SOC.1982,104, 6220. (3) Kim, M. S.; Dunbar, R. C. Chem. Phys. Lett. 1979, 60, 247.
The Journal of Physical Chemistry, Vol. 87, No. 11, 1983 1925
b ”
2
4
”
’
6
’
8
’
(0’
Pressure, 1(r5torr
Figure 1. ICR line width (half-width at half-height) as a function of pressure for C,H,I+ with bath gases: (A)C6H& (0) cyclohexane; (D) methane.
in the iodobenzene ion signal. In contrast, addition of a small amount of benzene or bromobenzene for example changed the intensity of the iodobenzene signal; the uncertainties introduced by such bath-gas reactivity led us to reject these molecules.
Results The line-broadening data can be analyzed by graphing the half-width at half-height of each peak against the pressure. A t low pressure the line width is the result of inhomogeneous broadening and is essentially independent of pressure. At sufficiently high pressures, however, the line width shows a linear dependence on pressure. The slope of this line (in units of radians) is equal to the momentum transfer collision rate constant, which is the collision rate constant, assuming the ion loses all its nonrandom velocity in each collision. This result can be derived from the ICR power absorption equation
where E is the amplitude of the applied radio-frequency field, r is the detect time, m and e are the mass and charge of the ion, and 5 is the collision frequency. This equation gives a Lorentzian line shape, whose width is proportional to the collision f r e q ~ e n c y . ~ If we set Z = Fe2r/(4m)for convenience,the absorption at resonance is A(w
w,)
= Z/[
(2)
At half-height then (3)
E=
(w - @l/2)
(4)
Graphs of line width vs. pressure for C6H51+with the bath gases iodobenzene, cyclohexane, and methane are shown in Figure 1. The quantity of interest for determining the number of collisions required to quench an excited ion is the orbiting collision rate, the rate at which an ion passes close enough to a neutral molecule to be drawn into an intimate collision complex. (Grazing collisions are unlikely to lead to energy transfer.) The orbiting collision rate ko can be related to the momentum transfer collision rate by the formula 0.9(M - m) ko N E (5) M (4) See, for example, Lehman, T. A.; Bursey, M. M. “Ion Cyclotron Resonance Spectrometry”, Wiley: New York, 1976.
1928
Lev and Dunbar
The Journal of Physical Chemistry, Vol. 87, No. 1 1, 1983
TABLE I collisions needed for quenching k,QGf kgRQdvf k , (or kb)=pe>f (k,ik,) 18f 3 13 7 i 2 2.5 * 1 4.0 f 0.4 10 0.08 + 0.02 0.33 f 0.04 50+ 15 CH, 10 0.8 f 0.2 1.8 k 0.2 5.5 f 0.7 7* 2 C-C6H1'l cm3 molecule-' s - * . Measured momentum transfer rate constant. a Rate constant in units of Orbiting rate constant derived from E. Theoretical orbiting rate constant. (See ref 7 . ) e Rate constant measured for two-photon quenching. f Uncertainties quoted d o not reflect the substantial systematic uncertainty in pressure calibration, which, as mentioned in the text, cancels o u t in calculating the last column of entries.
lo+ 2
C6H51
where m is the mass of the ion and M is the mass of neutral. (The approximate factor of 0.9 allows for the additional momentum transfer in grazing collisions; see ref 5). The collision rates measured in these expts. are listed in Table I. It should be emphasized that the quantity of ultimate interest is the collision number given in the last column, which, being a ratio, is independent of pressure calibration. The rates 5, ko, and k, in the table, taken separately, are dependent on the pressure calibration and are therefore approximate. An approximate pressure calibration was obtained from the ion pump current: this has been found by previous capacitance manometer calibration to be roughly correct for iodobenzene in this instrument; methane and cyclohexane readings were corrected by using the correction scheme of ref 6. No particular claim is made for the accuracy of these pressure calibrations: the rates may be taken as order-of-magnitude indications, but factor of two errors would not be surprising. Given also for comparison are the orbiting rates kgR calculated from the Langevin expression corrected for dipole effects following Barker and Ridge.' The laser results were analyzed with the two-photon formalism described previously,8 with the addition of a second collisional relaxation rate for the bath gas:
kbCBl
where B is the bath gas. This leads to the equation
_1 -- l a l + la2 + k,[C6H51] + kb[B] D
Pala2t
(7)
( D is the dissociation yield, -In (signalkht../signalkht When 1/D is graphed vs. the pressure of B (the pressure of C6H51is kept small and constant), as shown in Figure 2, the resulting line has slope a = intercept P =
lal
kb -
12UlU2t
+ l a z + k,[C6H51] PUlU2t
(9)
Using the value of k, derived from an experiment with iodobenzene as the only bath gas,g and making an as(5) Dunbar, R. C. J . Chem. Phys. 1971,54, 711. ( 6 ) Bartmess, J. E.; Georgiadis, R. M. Vacuum, in press. (7) Barker, R. A.; Ridge, D. P. J.Chem. Phys. 1976, 64, 4411. (8)Dunbar, R. C.; Fu, E. W. J. Phys. Chem. 1977,81, 1531. (9)(a) Lev, N. B. Ph.D. Thesis, Case Western Reserve University, 1982. (b) Lev, N.B.; Dunbar, R. C. Chem. Phys. In press.
61
0
0
a,
e. 7
I
-
8
8
0
.
.
2
&essure,
8
6 10-6
torr
10
Figure 2. The reciprocal of the dissociation (D = -in (signai,wton/ signal,, on) as a function of pressure for CBH,If with bath gases (0) Cyclohexane and (B) methane.
sumption about the relationship of u1 and a2,one can then find kb. a1 and a2 need not be equal, although detailed analysis of intensity and pressure dependence data for two-photon dissociation suggests that uz S a1 5 3u2 If we call the u2:a1 ratio R, so that a2 = Rul, the kinetics for the case that the bath gas is the parent gas can be solved to yield
It, =
a(1 + R ) 2
B2Rt
t 10)
This expression is quite insensitive to the value of R in the neighborhood of R = 1: variation of R over the range from 1/3 to 3 changes the calculated value of k, by only *15%. For the case of bath gas different from the parent gas, the expressions are more complicated,14but the conclusion is the same that the determination of k, is very insensitive to R. We will assign R = 1/2, and incorporate the uncertainty in k, arising from the unknown R into the reported uncertainty in k, values. It is often presumed that extensive ion-molecule energy transfer is likely only through the close contact of an orbiting collision, so that a comparison of ko with k, gives a direct indication of the number of collisions required for quenching. The outcome of this comparison is shown in Table I for each bath gas. IR-Visible Two-LaserExperiment. The results of experiments with methane and cyclohexane bath gases with simultaneous visible and infrared irradiation are shown in Figure 3, in the same format as Figure 2. The immediate observation is that the pressure-dependent behavior under two-laser irradiation is qualitatively similar to that under visible-only irradiation. To the extent reflected in these resuls, the photochemistry resulting from adding IR illumination is indistinguishable from that resulting from increasing the intensity of the visible laser. In extensive analysis of two-laser photodissociation of iodobenzene ions at a visible wavelength of 610 nm, it was concluded that the effect of the IR laser is to pump ions
The Journal of Physical Chemistry, Vol. 87,
Collisional Relaxation of Iodobenzene Ions
No. 11, 1983 1927
of two or three for iodobenzene ion.
2
I
0
3
P r e s s u r e c - c ~ H , ~10-6 ,
torr
5,
0
I
2 Pressure
4
CH,,
6
10-6 t o r r
Figure 3. 1/D as a function of pressure for (a) cyclohexane; (b) methane: (0)visible laser only; (0)visible and I R lasers.
from low internal energy up to an energy above the onephoton t h r e ~ h o l d .Within ~ ~ ~ the present model, this would suggest treating the effect of the added IR excitation by increasing the value of ul, giving the expression
Plots of 1/D against pressure do give lines similar to those for the one-laser experiment, with smaller slopes and intercepts. The assumptions about the nature of the two-laser enhanced photodissociation process embodied in eq 11makes possible a quantitative analysis for k,(2),the collisional quenching rate constant under two-laser conditions, which is of interest as a way of characterizing the IR-excited ion population. Unfortunately this analysis fails: this can be illustrated for the simpler case of parent neutral as bath gas, which shows the nature of the problem. Reduction of the kinetic equations for the two-laser case with parent neutral bath gas gives
L r
J
where p and R are as defined above for visible-only irradiation, and a2and p2 are the slope and intercept parameters for the two-laser case. For the present experiments p2/p lies between 0.5 and 0.7, so that this expression becomes extremely sensitive to the value of R . Since, as discussed above, R is poorly known, no meaningful determination of k,(2) is possible. Physically, this problem arises because under IR irradiation the u1 transition is quite highly saturated. One important conclusion can be derived, however: values of R smaller than 0.5 are absolutely inconsistent with the two-laser data within the analysis described here. This gives further support to the assertion that u1 and u2 do not differ by more than a factor
Discussion These results can be compared directly to the bromobenzene results of Kim and D ~ n b a r . The ~ number of collisions with methane required to relax the excited ions is essentially the same: -50 for C6H51+,more than 50 for C6H5Br+. The cyclohexane CGH5I' system has no direct counterpart in the C6H5Br+data, but the collision number is larger than the required number for benzene (4) and less than for propane (more than 20). The number of collisions required for C6H51+to be relaxed by parent neutral is more than the one collision reported for C6H5Br+with C6H5Br. However, the iodobenzene ion-iodobenzene neutral system seems to be similar to C6H5Br+with benzene (4 collisions) or fluorobenzene (3 collisions). It seems possible that the exceptionally efficient C6H5Br+quenching is the result of a long-range charge transfer process. If we assume energy transfer to be efficient only during orbiting collisions,the extreme limit of efficient quenching will occur when internal energy is fully equilibrated within each orbiting collision complex. This limit may be readily calculated by assuming the ion and neutral to reach a common vibrational temperature at each collision, and finding the number of collisions required to bring the ion from its initial energy of -2 eV to below 0.4 eV (which is the internal energy at which one-photon dissociation (the u2 process) is just possible). In this equilibration limit, iodobenzene bath gas requires between two and three collisions, cyclohexane about two collisions, and methane about fifteen collisions. From Table I it is seen that iodobenzene neutral as bath gas comes very close to quenching at the rate anticipated from this full-equilibration limit. This is not surprising, since the similar vibrational frequencies of ion and neutral, as well as the possibility of symmetric charge transfer, will favor efficient energy transfer within the intimate collision complex. On the other hand, quenching by either cyclohexane or methane bath gases is only about a quarter as fast as that expected on the full equilibration assumption; the orbiting collision complexes are far from reaching statistical sharing of internal energy between ion and neutral. For the case of the ion moving in its parent gas, charge-transfer quenching provides an alternative (or supplementary) mechanism to energy-transfer quenching. We should consider briefly how this is expected to affect the observed rates. Assume, for lack of other knowledge, that nonorbiting charge transfer occurs by long-range electron exchange, with no transfer of either momentum or internal energy between ion and neutral. (Short-range symmetric charge transfer occurring during orbiting collisions is effectively equivalent to any other orbiting collision for this purpose. But note that the possibility of symmetric charge transfer during orbiting collisions gives additional, and strong, grounds for expecting the parent neutral to be the most effective quenching gas.) On this assumption, each long-range charge transfer event will give complete momentum quenching and also complete internal energy quenching, so that f and k, should be equal. As we have seen, the experimental uncertainties in E and k, for iodobenzene neutral allow the possibility that they are equal, although the best values favor the conclusion that f > k,. Thus a contribution to k, from long-range symmetric charge transfer is not inconsistent with the data, but the data suggest a predominant contribution to quenching by orbiting energy-transfer collisions in which f can be greater than k,. In evaluating the rates of quenching by relatively inefficient quenching gases where the equilibration assumption
1028
J. Phys. Chem. 1003, 87, 1928-1931
fails seriously, possible assumptions are that each collision removes a constant amount of energy, independent of the initial internal energy, or that each collision removes a constant fraction of the initial energy. Rossi and Barkerlo claim to have demonstrated that the second model describes energy transfer from excited azulene to cold azulene, and this model is also used by Houriet and Futrell" in analyzing energy transfer from (C5H9')* to methane. The present experiments cannot distinguish between the two possibilities and provide only the total number of collisions to quench. If we assume constant energy loss per collision, a methane collision would remove about 300 cm-', a cyclohexane collision about 2000 cm-', and an iodobenzene collision about 6000 cm-'. If the ion loses a constant fraction of its energy on each collision, that fraction would be -50% for C6H,I, 20% for cyclohexane, and 3% for methane. Other studies of energy transfer from ions have yielded a variety of results. The results of Kim and D u n b d have already been discussed. For collisions of C5Hg+with CHI in a tandem ICR, the average energy transferred was found to be 1400 cm-l." Rosenfeld et a1.I2 reported that ap(10) Rossi, M. J.; Barker, J. R. Chem. Phys. Lett. 1982,85, 21. (11) Houriet, R.; Futrell, J. H. in 'Advances in Mass Spectroscopy"; Daly, N. R., Ed.; Heyden: London, 1978 Vol. 7A.
proximately 100 collisions are required to cool CH30HFformed with 15 kcal of excess energy, when the colliding gas is methyl formate. Freiser and Beauchamp13found that, in a two-photon ICR experiment like the one described here, CH3CN was approximately 25% as effective in quenching excited benzene ions as benzene itself. A range of collision efficiencies has thus been reported, with no systematic explanation of which factors determine the efficiency. Further studies, with a systematic variation of the properties of the bath gas, are in progress. Acknowledgment. The support of the donors of the Petroleum Research Fund, administered by the American Chemical Society, and of the National Science Foundation, is gratefully acknowledged. N.B.L. acknowledges with gratitude the support of a Goodrich predoctoral fellowship during part of the period of this research. Registry No. C6H51+,38406-85-8; CBH& 591-50-4; CsHI2, 110-82-7;CHI, 74-82-8. (12) Rosenfeld, R. N.; Jasinski, J. M.; Brauman, J. I. J. Am. Chem.
SOC. 1979,101, 3999. (13) Freiser, B. S.; Beauchamp, J. L. Chem. Phys. Lett. 1975,35, 35. (14) We note for completeness the expression analogous to eq 10 for a bath gas different from the parent: 2/32
+-
R2t2
Fluorine-I9 Relaxation Study of Perfluoro Chemicals as Oxygen Carriers PeJmanParhaml and B. M. Fung' Deperrment of Chemistry, University of Oklehoma, Norman, Oklahoma 73019 (Received:November 4, 1982; In Final Form: December 27, 1982)
Fluorine-19 magnetic relaxation of fluorine atoms in cis- and trans-perfluorodecalin,perfluorotributylamine, and an emulsion of perfluorotributylamine in water was studied at 75.38 MHz and 298 K. It was found that the longitudinal relaxation rate (l/Tl) of each fluorine nucleus depended linearly on the partial pressure of oxygen in mixtures of N2 and O2that were used to saturate the liquids. The slopes of the plots were different for each type of fluorine atom in a perfluoro chemical. This was explained by the preferential approach of oxygen to some parts of the organic molecule over other parts. This is likely due to steric effect rather than specific binding.
Introduction A number of perfluorinated organic compounds is widely used as blood substitutes.' They are often called perfluoro chemicals (PFC). The PFC's can be used as blood substitutes because they are good carriers of oxygen and carbon dioxide, inert, nontoxic, and can be transpired from the body. Over the past 16 years, a great deal of progress have been made in the field of PFC blood substitutes.',2 Numerous experiments on animals have been performed,'J and a number of clinical tests has been reported recently.H (1) J. G. Riess and M. LeBlanc, Angew. Chem. Znt. Ed. Engl., 17,621 (1978). (2) R. P. Geyer, K. Taylor, R. Eccles, T. Zerbonne, and C. Keller, "Abstractof Papers",183rd National Meeting of the American Chemical Society, Las Vegas, NV, Mar 28-April 2, 1982; American Chemical Society: Washington, DC; FLUO1. (3) T. H. Maugh, 2nd, Science 206, 205 (1979). (4) E. R. Gonzalez, J. Am. Med. Assoc., 243, 720 (1980). (5) K. K. Tremper, R. Lapin, E. Levine, A. Friedman, W. C. Shoemaker, Crit. Care Med., 8, 738 (1980). (6) K. Honda, S.Hoshino, M. Shoji, A. Usuba, R. Motoki, M. Tsuboi, H. Inoue, and F. Iwaya, N . Engl. J. Med., 303, 391 (1980).
The most commonly used PFC's to date are perfluorodecalin (octadecafluorodecahydronaphthalene), per, fluorotripropylamine (heneicosafluorotri-n-propylamine) and perfluorotributylamine (heptacosafluorotri-n-butylamine). In preparing a blood substitute, one or several PFC's are usually emulsified in a Ringer's solution, using Pluronic F 68 (a block polymer of poly(ethy1ene oxide) and poly(propy1ene oxide)) as a emulsifier. Other PFC's and fluorinated surfactants developed recently can form more stable emulsion^.^ While hemoglobin has a definite binding for molecular oxygen, PFC's probably act as simple solvents for oxygen and other gases.2 The volume of oxygen dissolved in the (7) R. C . Xiong, Chung-hua Wai R o Tsa Chih (Peking),19, 213 (1981); MEDLINE 0530118 81260118 (1982). (8) T. Suyama, K. Yokoyama, and R. Naito, b o g . Clin. Biol. Res., 55, 609 (1981). (9) R. E. Moore and L. C. Clark, Jr., "Abstract of Papers", 183rd National Meeting of the American Chemical Society, Las Vegas, NV, Mar 28-April 2,1982; American Chemical Society: Washington, DC; FLUO5; manuscript submitted for publication.
0022-3654/83/2087-1928$01.50/00 1983 American Chemical Society
