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
