NOTES
Oct., 1963 removed a t the temperature of our analyses, 750'. Analysis numbers correspond to run numbers in Table I and indicate that the powdered sample has had the same outgassing treatment as the rod in the same numbered adsorption experiment. Some of the water obtained comes from the combustion of hydrocarbon impurities and this has been estimated by assuming that the hydrocarbon combustioii gives one molecule of H20 for each molecule of GOz. Subtracting this amount gives the figures in parentheses for hydrogen present on the glass surface either as free water or as hydroxyl TABLE I1 AXALYSISFOR CARBOX AND HYDROGEN Analysis Ha0, mg./g. coz, rng./g. (*0.3) (=to.3) 1 35.1 (32.0) 7.5 2 3
4
21.6 (20.0) 9.9 ( 9.9) 12.3 (11.8)
3.8 0 1.3
groups.6 Table I1 mill give an indication of amounts of contaminants in adsorption experiments although the correspondence may not be exact. The COz obtained in analysis 4 probably came from material picked up during prolonged exposure to water vapor as analysis samples were not protected by all-metal valves. Similar contamination did not occur in run 4 since there was no blackening of the rod after the final heating a t 300O. Discussion It is clear from the isotherms, which cover a range which includes the change of slope in expansion plots1 and a phase transition in a similar system,3 that there is no phase transition for the present system in the range covered. It is also apparent that variation in outgassing procedures has an appreciable effect on the isotherms and that there is a close relation between this effect, as shown by variation in either C or v, and amount of surface contaminant. This variation in Vm , and hence in the B.E.T. surface area, presumably arises from a variation in the nature of the surface, since outgassing temperatures were too low to cause appreciable sintering, and comparison of experiments 3 and 4 shows that the surface area is increased on reintroducing water contaminant. It is well known' that porous Vycor glass adsorbs hydrocarbon impurities from the atmosphere, but it appears from these results that hydrocarbon contamination is much less important than water contamination, as judged by surface covered. For example, assuming that the hydrocarbon contaminant is present mainly as --CHZ- groups (cross-sectional area 4.9 A.2) and that parenthesized figures in Table I1 represent run 1 and free water (cross-sectional area 10.8 k2), analysis 1indicate that after outgassing at loo', the remaining water covers about 90% of the surface and hydrocarbon about 4%,. While these estimates are approximate, since some hydrogen will be present as hydroxyl groups, the order of magnitude will be correct. After outgaming at 300', the hydrocarbon contaminant had undergone considerable decomposition, as shown by the color of the rod, and after treatment a t 450' in oxygen had been completely removed as shown (6) T. R.Elmer, I. D. Chapman, and AI. E. Nordberg, J . Phys. Chem., 66, 1517 (1962). (7) M. E. Nordberg, J. Am. Ceram. Soc., a7, 299 (1944).
2227
by the appearance of the rod and analysis for carbon. That considerable mater contamination (as hydroxyl groups) remains after heating a t 450' is in accord with other measurements. It is also noted that the reaction between water vapor and the surface a t room temperature, which produces contamination (presumably hydroxyl groups) not removed by heating a t 300', is probably a slow one siiice isotherm 4 is much closer to 3 than to 2 and similarly for the analyses. This again is in accord with Kordberg's observations.6 Acknowledgments.--We are grateful to the Corning Glass Works for the gift of Vycor glass and to the Microchemical Laboratory of the University of Otago for carrying out the analyses. We also acknowledge financial support from the New Zealand TJniversity Grants Committee.
THE REACTION OF HYDROGEN ATOMS WITH NITRIC OXIDE BY R. SIMONAITIS Department of Che?nistry, University of California, Los Sngetes, Califoinia Received Februaru $7, 1968
The isothermal calorimeter method for the study of hydrogen atom reaction kinetics was first developed and applied to the study of hydrogen atoms with acetylene,l ethane,z and methane3 by LeRoy, et al. The results in the case of ethane and methane have not been generally accepted. Schiff 4 ~ 6extended the method to the study of oxygen atom recombination in the presence of oxygen molecules and nitric oxide. The results compared fasvorablywith those of other methods. Dickens, et. al.,O repeated Schiff's work on the recombination of oxygen atoms in the presence of oxygen gas and showed that atom transport by diffusion must be considered in the analysis of data. The kinetics of the reaction of hydrogen atoms with nitric oxide was investigated by Clyne and Thrushn7 The rate was followed by measuring the intensity of the red emission by the excited HNO. The mechanism was shown to be ki
H
+ NO + A I +HKO + M
followed by the rapid reaction ka
H
+ H E 0 +H, + KO
k, was found to be 4.8 x 1015cc.2/mole2sec. a t 294'.K., when &I = H2; the activat'ion energy is 0.7 f 0.3 kcal./ mole. It' is the purpose of this note to report the results for the above reaction as determined by the isothermal calorimeter technique and to discuss t,he effect of the presence of the probe upon the atom concentration in t'he reactor. (1) J. R. Dingle and D. J. LeRoy, J . Chem. Phys., 18, 1632 (1950). (2) M. R. Berlie and D. J. LeRoy, Discussions Faraday Soc., 14,50 (1953). (3) M. R. Berlie and D. J. LeRoy, Can. J . Chem., 82, 650 (1954). (4) H.I. Schiff, L. Elias, and E. A . Ogryzlo, ibid., 37, 1680 (1959). (5) E. 8. Ogryzlo and H. I. Schiff, ibid., 31, 1690 (1959). (6) P.G.Dickens, R. D. Gould, J. W.Linnett, and A. Richmond, Nature 187,686 (1960). (7) M. A. A. Clyne and B. A. Thrush, Trans. Faraday Sac., 67, 1305 (1961).
Experimental Matheson nitric oxide (9976 min.) was subjcctcd to t)iill) to bulb distillation, retaining only thc middle fraction, until the resulting solid material was colorless. Ifydrogen was pashed through 20cm. platinized asbestos at ~100’to remove traces of oxygen and was dried by passage through several traps containing silica gel a t liquid nitrogen temperature. The apparatw was essenthlly that desc~ibedby Scfliff.4 1 1 ~ drogen atoms 13 ere produced by subjecxtlng hydrogen gas t o :I microwave discaharge (2450 Mc./sec.), and thc hydrogcn :Ltoin decay along a cylindrical reactor, 2.3 (‘in. in d w n e t e r :ind 30 (mi. long, was followed by a movable isotherinul probe. l‘hc probe was a 36 I%.S.gage platinum nire, 23 cni. long, wountl into II coil. The atom concentr,ition nv~b(*:d(ul:Ltcd frorii thc ho,it I i t w i ated when the detector W:L* opwited undri isotliwniul trnditiori.. Iiimir flow vclociticr of u h i t 110 ( * i n . m . ~ i i d:L tc1(,11 piessure of 2 to 4 inm. were U b d . (
Results It was observcd that if a sccoiid probe is placcd dowiistream from the first oiir, thr atom concentration registered by the latter nil1 decrcasc ith decreasiiig distance betnecn t h r two probcs; thciscfoi*c, it is calcar that the probr iiiflucncrs the atoni coiiccntratioii. This probe erfcct is considcrcd iii tlic analysis that follo\v5. Thc hydrogeii atom decay nas foulid to tw first order in hydrogcii atoms, hydrogcii molecules, i.r. M, and iiitric oxidc molecules, i i i agreemciit with Clyrie arid Thrush. For a statioiiary state of I I S O
+
dIS,/dt = [ k ~ ~X.I(SO)(AI)](II)= k’(l1)
(I)
where lZ11 is for the reaction 21T
+ wa11
---it
IT,
+ wall
The equation of continuity for hydrogen atoms is -L)du2/d.P
+ Ir0dii/d.c + Xn = 0
(2) whcre I ) is the binary diffusion coefficient, Vo is tlie linear flow velocity, n the atom concentratioii, and li the first-order rate constant, which is k11 arid k’ in the absencr and in the preseiice of SO, respectively. 1Squation 2 coiisitlers atom transport by flow and axial diffusion, but neglccts radial difhioii and the small change in the linear velocity over tlie rcaction zoiie. Consideriiig the protw as a circular disk cxtendiiig ovcr the cross secatioii of tlie reactor, cq. 2 is subject to the boundary conditions 71.
=
no at
.2:
= 0, dn/d.2:
+ ? n / =~ 0 a t r = 1,
where L is tlic position of the probc a i d m is a coiistaiit, equal to V O / D k,,/D; I;,, is t h t rate constaiit for the recombinatioii of hpdrogcn atoms 011 platiiinm. ‘I’hc solution is
+
L
At large distances of the probe from the origin, i.c. for large L, terms coiitainiiig are very srnall; thus (3) reduces to
vliere u10 is tlic atom coiicciitratioii a t IJ1. I‘rom ccy. 111 nl”,72 s. I,‘ should be linear, with slopc s = -ri. Good liiiear plots wcrc obtained, botli i i i the preseiice and abse11ce of nitric oxide. The rate coiistant li is calculated from the equation 4 a plot of
k
=
5.WD
+ 2.3sr”
(3
The valiie of kl calculated from (1) and ( 5 ) is 11.0 X 10’j cc.2/molc2 sec. at 298’ I was calculated by Amdur.8 IGquatioii 3 is identical with the one derived from eq. 2, when the boundary conditions are n = 0 at 2 = 03 and 11 = no at 5 = 0 ; these t)ouiidary contlitioiis correspond to tlie absence of the probe.6 ‘l’hn effect of the probe is to change the atom coiicentratioii a t the position of the probe by the constant factor (TI - r 2 ) / ( r 2 m),providing the probe is a t a sufficient distance from the origin. Acknowledgment. -.The author wishes to rxprrss his appreciation to l’rofcssors R. Hardwick and I
