F/g 7/4 . fllfl/ll/lfl EE2hIIEIIIhhEEThis interim report was submitted by The Aerospace Corporation,...
Transcript of F/g 7/4 . fllfl/ll/lfl EE2hIIEIIIhhEEThis interim report was submitted by The Aerospace Corporation,...
AD-AO79 613 AEROSPACE CORP EL SEGUNDO CA AEROPHYSICS LAB F/g 7/402 (1 DELTA)-? ATOM KINETIC STIJDIES.(U)NOV 79 Rt F HEIDNER. C E GARDNER F04701-79-C-0060
UNCLASSIFI ED TR-008015606)-2 SD-TR-79-6 NL
". fllfl/ll/lflEE2hIIEIIIhhEE
m o2h hh80h
0 (A)-I Atom Kinetic Studies
R. F. HEIDNER and C. E. GARDNER
El Segundo, Calif. 90245
DDC8 November 1979
,~JANIgOInterim Report LL]
APPROVED FOR PUBLIC RELEASE;DISTRIBUTION UNLIMITED
Prepared for
AIR FORCE WEAPONS LABORATORYKirtland Air Force Base, N. Mex. 87117
SPACE DIVISIONAIR FORCE SYSTEMS COMMAND
Los Angeles Air Force StationP.O. Box 92960, Worldway P tal CenterLos Angeles, Calif 1 17 0
This interim report was submitted by The Aerospace Corporation,
El Segundo, CA 90245, under Contract No. F04701-79-C-0080 with the
Space Division, Deputy for Technology, P.O. Box 92960, Worldway Postal
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Aerospace Corporation by W. R. Warren, Jr., Aerophysics Laboratory.
Lieutenant S. C. Garcia, SAMSO/DYXT, was the project officer for
Technology.
This report has been reviewed by the Information Office (01) and is
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This technical report has been reviewed and is approved for publica-
tion. Publication of this report does not constitute Air Force approval of
the report's findings or conclusions. It is published only for the exchange
and stimulation of ideas.
mes C. Garya, Lt, USAF .eph . Ca, Lt 4 ol, USAF,--Poject Officfr 6hief, Advanced Technology Division
FOR THE COMMANDER
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and AnalysisDeputy for Technology
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IS. SUPPLEMENTARY NOTES
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Electronically Excited Oxygen I AElectronic Energy Transfer1Flow-Tube Kinetic Studies Ip-A -?~Gas Mixing 'rCW Iodine Laser ( 4 AW o s
20. ,ABSTRACT (Continue an reverse side If necessary end identify by black number)
A discharge flow !.ystem has been used to refine kinetic rate measurementsfor the O2(1LA) + 17' energy-pooling process and for the iodine- catalyzed re-moval of O2(1A). Particular attentio{A/ras givenithe effects of I2-carrier gas(Ar) on the emission intensity of O2 (itA) and Oa2it). A heated 12 saturator anda saturator bypass technique were developed to minimize such e-urc-s. Thedata reported here indicate that processes proportional tck,(I2)A) are im-portant at [Oa(1A)I and [IYI densities, which are appropriate lra cw O2 (1 tA)-Iatom transfer laser.,
FOM 7 UNCLASSIFIED
CONTENTS
I. INTRODUCTION 7............................... 7
II. EXPERIMENTAL .............................. 11
III. RESULTS .................................... 17
A. Influence of Injected Ar on 0 (1A, 1Z) IntensityM easurem ents ................................. 17
IB. Energy Pooling of I with O2( A) ................ 20
IC. Iodine Catalyzed Removal of O ( A) .............. 26
IV. DISCUSSION .................................. 35
V CONCLUSIONS ................................ 39
APPENDIXES
A. Chemical Kinetics of the 2( 1A)-I Atom System ........ 41
B. Rate Coefficients for the Kinetic Model ofAppendix A ............................... 43
Acces5of r
'... ..
-1-
FIGURES
1. Electronic Energy Levels in O -12 System ................. 8
2. 12 Dissociation Cycle in 0 2(A)-I Atom Transfer System . . . 9
3. Schematic of O-I Diagnostic Methods ...... ............... IZ
4. Vapor-Pressure Curve for 1. ...................... 14
5. Variation of 0(A, 2 ) Emission with Ar Injection .......... 186. Effect of Ar on 16340 Versus [O2( A)]2 ................ 19
7. Determination of k 2 without Saturator Bypass Technique. . . . 23
8. Determination of k 2 by Use of Saturator Bypass Technique . . 25
9. Time-Dependent O 2 (1A) Dimol and 02( L) Emission in thePresence of 1 ................................. Z8
10. Time-Dependent First-Order Decay of O(I A)(X = 1. 27 4m) Versus 12 .......................... 29
Ii. Determination of kef f with First-Order Decay ofO2( A) Assumed ........... .............................. 31
12. Time-Dependent Second-Order Decay of 0 (1A)(X = 1. 27 Lm) Versus 12............' .......................... 32
13. Determination of k + k' with Second-Order DecayKinetics Assumed @or Z( .A) ...................... ... 33
-3-
i TABLES
I . Spectroscopy of the 02-1 Atom Transfer System .. .. .. ...... 13
I. Flow System Reactant Contact Time. .. .. ... .......... 16
4 I.Comparison of Kinetic Results .. .. .. ...... ......... 34
5
I. INTRODUCTION
Workers at AFWL recently demonstrated an efficient, chemically
pumped, cw electronic transition laser that is based on the o?('A)-I atom
transfer system.
k 1 3 2
o0(A) + .1( / o3Z) +I P.)
The intent in this technical report is to supplement and, where necessary, to
revise the conclusions reached in earlier studies on this transfer system. 2
The nomenclature and rate-coefficient numbering scheme introduced in the
pioneering studies by Derwent and Thrush 3 - 7 are used in this report. For
reference, the relevant spectroscopic energy levels and the logic flow chart
of the OZ(IA)-I atom transfer system are reproduced from Reference 2 and
appear as Figs. I and 2.
1 W. E. McDermott, N. R. Pchelkin, D. J. Benard, and R. R. Bousek,"An Electronic Transition Chemical La.er," App1. Phys. Lett. 32,469 (1978).
2 R. F. Heidner III, J. G. Coffer, and C. E. Gardner, O2(IA) - I AtomEnergy-Transfer Studies: CW Inversion on 1. 315 pim I-Atom Transition,TR-0078(36i0)-i, The Aerospace Corporation, El Segundo, Calif.(15 Dec. 1977).
3 R. G. Derwent, D. R. Kearns, and B. A. Thrush, "The Excitation ofIodine by Singlet Molecular Oxygen," Chem. Phys. Lett. 6, 115 (1970).
4R. G. Derwent and B. A. Thrush, "Measurements on Oz(IAg) and O2(IE+)in Discharge Flow Systems," Trans. Faraday Soc. 67, 2036 (1971).
5 R. G. Derwent and B. A. Thrush, "The Radiative Lifetime of theMetastable Iodine Atom I(5 2PI/ 2 )," Chem. Phys. Lett. 9, 591 (1971).
R. G. Derwent and B. A. Thrush, "Excitation of Iodine by SingletMolecular Oxygen," J. Chem. Faraday Soc. II 68, 720 (1972).
7 R. G. Derwent and B. A. Thrush, "Excitation of Iodine by SingletMolecular Oxygen," Disc. Faraday Soc. 53, 162 (1972).
-7-
H 20
C? 15 -0211+)
3-7E 5239 cm-1
02(161
11803 cm1
5
7603 cm-1 7882 CM1
0 02 1--2
Fig. 1. Electronic Energy Levels in 0 1~ System
-8-
17
02 ('A) 02 ('A) ---(1' A)41!1 + 0 31
-9-j
022
/I +IAL02111
f t
02 ig. 02.1 12 Disocat+i Cycle in* 2,Atom Tranfer System :
In this study, refined experimental methods were used, and conclusions
quite different from those of Derwent and Thrush were reached. These new
observations are of critical importance in the continued development of the
cw I*' laser that is based on energy transfer from O 2 (IA).
Io
-.10-
ti II. EXPERIMENTAL
The experimental apparatus is depicted in Fig. 3. 02(1A) is produced
by a microwave discharge in pure 02, and the 0 atoms that are simultaneously
produced recombine on a heated HgO surface. The absolute concentration of0 2 (1 A) was measured by means of an isother-1 al calorimeter method that is
described in detail in Reference 2. Spectro: opic methods were calibrated
against the probe measurements. The relevant spectroscopic features of the
0z-1 atom system are summarized in Table I.
The 12 carrier gas was Ar. It flowed at atmospheric pressure
through an 12 saturator enclosed in an oven. A three-station digital thermo-
couple was used to monitor the temperature of the saturator. The Ar + 12
was metered by means of a stainless steel needle valve held at a temperature
several degrees warmer than the saturator. Partial pressures of I in Ar
were calculated from the vapor pressure data of Gillespie and Fraser (Fig. 4).
Mole fractions of 12 in Ar of (5 - 10) X 10-3 were obtained at saturator tem-
peratures of 60 to 70°C.
The quality of the kinetic data was improved markedly when a "saturator-
bypass" arrangement was used to inject the Ar + 12 into the 0 2 flow.
This arrangement permitted a constant flow of Ar to be continuously injected
into the 02 stream and a measured fraction to be saturated with I Thus,
the partial pressure of Ar in the flow remained constant while the concentra-
tion of injected 12 was varied.
Two methods of obtaining decay plots of 0 2 ( A), 02(Ir), and I' were
used. The Ar + 12 could be shunted to one of three fixed injectors (A, B, or
C), with the optical detectors used to monitor a fixed position on the flow
tube. Alternatively, a single injector was used, and the detectors were
8L. J. Gillespie and L. H. D. Fraser, "The Normal Vapor Pressure of
Crystalline Iodine," J. Am. Chem. Soc. 58, 2260 (1936).
A r
D A CHART SCP
I I ~THERMOMETERTRNIT
LOCK-IN PHOTONCOUNTER
SATURA ORp
r-- Ge GaAsI j PMT
0. I25 m 0.25 mI IIR VISIBLI
Fig. 3. Schematic of 0 -I Diansi ehd
2Nogwsi Mthd
S. Sfn Ln Sn -. n Smcm Nl N 70'
41 >4 O
0 S0
v ou -u 0 "S ' I
I-, .o IS' '0X
41 "d:I n 0
w 0 u
+1 N D 0o s
M "D
41 ~ ~ ~ ~ b u ' 41 I, 1"41~ ~~~ ISSN 4o 10'
41t > a S.41 41 4
o~~ +1 "g N 04-0~
Q '0 -o x 1<
0 Z.
o o~
0413 r
'a+ Uo U .0 414 z'O Z '.
4-'0 40 4 * .5 -. v -
:* Ua U PQ oro to. Z X*
be +1 bo r' c Ca a~ 41G 1
aS ~ ~ m 411 ' 5
0 41 ?: -
$4~M 'a14 Id.-4'Ix a'
0c .04 ' 0. u to0
IS' Co1 ' U -0 'aaUO~ ~~ ~ -0+ N.u
0 4
10 .10.0
1.0
0.12.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5
T_1x 10 3K_1
Fig. 4. Vapor-Pressure Curve for 1 2 (Ref. 8)
- 14-
translated along the flow tube (Positions 1, Z, 3, and 4) on a movable platform
mounted on a ball bushing rail system (Thompson Co.). The relationship of
the injector-detector positions to the contact time of the reactants is given in
Table II, e. g., B-2 indicates that Injector B was used with the detector at
Position 2.
The flow tube was made of square quartz (2.0 X 2.0 cm i.d.) and was
internally coated with Halocarbon wax. Deposits of iodine oxides could be
observed occasionally; however, mild external heating from a heat gun
restored the original properties of the Halocarbon surface.
-15-
Table H. Flow System Reactant Contact Timea
Contact Time, msecDetecto rPositionb Injector Position
A B C
1 52 90 128
z 73 iii 149
3 94 132 170
4 115 153 191
aTable entries must be divided by the volume
flow rate V(l/sec) to obtain the contact time inmilliseconds. Typically, V = 1.0 1/sec.
bSee Fig. 3.
-16-
III. RESULTS
A. INFLUENCE OF INJECTED Ar ON O2( A, im)
INTENSITY MEASUREMENTS
In earlier experiments carried out in this Laboratory, 2 He was used as
a carrier gas for IZ instead of Ar. However, severe gas dynamic effects are
possible when He is injected into 02P because the viscosities are so different.
It was hypothesized that the use of an Ar carrier would greatly alleviatc this
problem with only a small change in the partial pressure of Oz -
This hypothesis was explicitly tested by injecting Ar counter to the O?flow through L-shaped injectors (Fig. 3). Clyne evaluated the mixing times
characteristic of similar arrangements. From his studies, a mixing time of
5 rnsec was predicted. The partial pressures of 02 and Ar were calculated
on the basis of complete mixing with the conventional formula
1 PTOT (Z)
where the rh. are molar flow rates.1
The decay times of 2(1A) were essentially unchanged by the injection
of Ar into the flow of active O. The intensity of both the "dimoll emissionand the Oz(IT) emission, both proportional to [O2(iA)]Z, decreased markedly
with Ar addition; however, the ratio of these two intensities remained roughly
constant (Fig. 5). Theoretically, a plot of 16340 versus [O 2 (1 A)]? calculated
from Eq. (2) should be a straight line; but, as demonstrated in Fig. 6, there is
9 M. A. A. Clyne and H. W. Cruse, ''Rates of Elementary Reactions Involvingthe BrO(X 2 Tr) and IO(X 2 7T) Radicals," Trans, Faraday Soc. 66, 2214 (1970).
-17-
4
6f340
3
'7619
CO
'6340
00.5 1.0
P r Torr
Fig. 5.Variation of 0,('A, ~ Emission withAr Injection
-18-
0.9-
_0.8-
CnC
B0.6 -3 A
1.0 0.95 0.90 0.85 0.80
2 2 calculated
Fig. 6. ]Effect of Ar on 1 6340 Versus[02(az
-19-
a substantial deviation from linearity. Three possible explanations for this
behavior are:
1. The O 2 and Ar are not completely mixed.
2. The increase in system pressure with Ar addition has aneffect on the 0 2 (IA) production mechanism.
3. The addition of Ar has an effect on the dimol emissionmechanism.
The first explanation is supported by the fact that the dimol emission in-
creases as a constant mass flow of Ar is injected farther upstream (A - B - C).
The measured intensity deviation from the gas dynamic predictions (25% low
for hAr /rho? = 0.4) is rather small. The second explanation given may be
valid also since the system pressure increases by approximately 25% for
rhAr/rho 2 = 0.4. Evidence for the third possibility has been cited recently
at AFWL;* however, as demonstrated in Fig. 5. this effect is minor in the pre-
sent system unless compensating errors exist for 02( 1E) and dimol emission.
The correct evaluation of the kinetic effect of I? (and therefore I atoms)
on electronically excited 02 requires that the amount of Ar carrier be limited
to approximately 10 to 20% of the 02 mass flow. This constraint mandates
the saturation of the buffer gas stream with IZ at elevated temperatures. The
"1saturator bypass" technique is equally important since it permits the mixing
of Ar with O? to be identical as the partial pressure of 12 in the Ar is increased.
Tiie total pressure is, thus, held constant, and, therefore, the discharge produc-
tion of Oz(IA) should also be constant.
IB. ENERGY POOLING OF I: WITH 02(.-
It is a generally accepted fact that O2(1I) is enhanced by the addition of
I2 to a stream of electronically excited 02. The mechanism is as follows:
D. Benard, private communication, 1978.
-20-
k 3?
0O 2 ( A ) + I --- + 0 213 : (3) -
k5
O2(IA) I* - 2; 4
Unfortunately, earlier work in this Laboratory and also by Derwent and
Thrush 3 - 7 failed to give the general analytic expression for the function
0 2 (ilZ) = f(1 2 ), which correctly describes the time-dependent removal of 0 2 (tA)
by I atoms. The simplest analytic approximation was derived in an earlier
study, Eq. (B-13) of Reference 2, where 1Z10 represents the steady-state
-1= 2 (5)
10 k 9 (k 5 + k 6 ) [Oz(3M)]
concentration, which results from O(I A) energy pooling with no I., i. e,
k
O( 1A) + 0 2 (1 A) 0 02(1 Z) + Oz(3Z) (6)
Two processes reduce the [0 2 (1 A)] between the Ar + I? injector and the1 0fluorescence region, thus reducing O2( Z) 0 . They are:
1. The previously discussed gas dynamic perturbations causedby the Ar carrier gas introduced with the I Z .
2. The I-atom catalyzed removal of 0 2 (IA), which is discussedin the Section III. C.
Thus, a variation of Eq. (B-i ) of Reference 2 must be applied in order to
properly evaluate k2 . Either of the following two expressions will provide
proper analytical forms for determining k 2 :
-12 -
~Z 1640k k,\ 6340 k (k5 + k6) [i(3E
( .kk [i] (8)TO '1.- 27 / k 9 :k(k 5 + k 6 ) [02( 31)]
Two experimental approaches were applied to measuring k 2 . In the first
approach, considerable data reduction and system modeling are required.
It is presented in order to demonstrate the errors introduced by gas dynamic
problems.
From Eq. (B-6) of Reference 2, the expression can be written
1 0 / \i/Z2(-64."27 = exp(kff[I])t (9)
0(tN) 16340) 1 1.27
where keff is a measured rate coefficient equal to [kIk6 /(k 5 + k 6 )] + k7
(Section UI.C), and t is the time between 12 injection and 02('Z) monitoring.
The 16340 cannot be monitored directly since 12 (B -. X) emission is too great
to permit the higher values of 12 addition, which are of interest. The It. 27
can be monitored directly, however. Figure 7 is a plot of the three stages of
data reduction: (1) the raw (I7619/I0619 - i) versus [I]/[02(3Z)] data,
[Eq. (5)] (Curve A); (2) the data corrected for the gas dynamic reduction of
the [0 2 ('A)]2 by use of the results presented in Fig. 6 (Curve B); and (3)
doubly corrected data that incorporate the gas dynamic correction and the
correction derived from Eqs. (8) and (9) (Curve C). This last plot is roughl-
linear and yields a value k2 = 2. 5 x 1010 cm 3 /mol-sec.
2 Z
k .....-..-
PI (Tord x 103
0.5 1.0 1.5 2.0 2.5
5/C
krducio of . -... , -- -
3-Z3
0.25 0.50 0.75 1.0
[111[3213}), X 103
Fig. 7. Determination of k2 without Saturator Bypass Technique.
A, raw data; B, data corrected for gas dynamic effects;
C, dat.a corrected for gas dynamic effects and for linear
k ef f reduction of 0 2(I
The second experimental method is much more reliable. As described
in the experimental section, the "saturator-bypass" method of controlling theAr concentration was used. A constant-mass flow rate of Ar was injected
into the active 02, and a varying fraction of this flow was passed through the
I? saturator. Thus, the total pressure in the system remained constant
(to approximately 0. 3%), and gas dynamic corrections to partial pressures
were eliminated. The fundamental emission signal of 0 2 (1 A) at . 27 ILm is
not overlapped by any other spectral feature except for I" at 1.315 pLm. This
latter problem was eliminated by the use of very narrow slits on the near
infrared monochromator. Thus, experimental values of I0 . 27/I1.27 could
be provided as input to Eq. (8). At PTOT = 3.67 Torr, k2 = 5.5 X 1010
cm 3 /mol-sec was determined, and at PTOT = 1. 69 Torr the result was
k = 4. 6 X 1010 cm 3 /mol-sec (Fig. 8). Therefore, the best value of the
I -O2(iA) energy pooling rate is
k2 = (5.0 ± 1.0) x 1010 cm 3 /mol-sec (10)
where the error reflects the uncertainty in the amount of 12 added, but not
the uncertainty in the quantity ki/k 9 (k 5 + k6 ) required to solve Eq. (8). The
result is approximately three times faster than that reported by Derwent
and Thrush, 7 i.e., k 2 = (1.6 ± 0. 2) x 1010 cm 3 /mol-sec. The quantity
k i /(k 5 + k 6 ) was shown to be cloqmely approximated by the equilibrium con-
stant for Process (i),2,7 i.e., KEQ= k,/k 5 L k 1 /(k 5 + k 6 ). The 0 2 (IA)
ene rgy-pooling rate
k 9
02(1A) + o (1A) -. o2(1M) + oz(32:) (6)
4has been reliably measured only once, and any error in that quantity is
reflected in the reported value of k 2 .
-24-
PlITorr) x 103
0.3 0.6 0.9 1.2 1.5 1.8
8-
6-
N4
1 2 3 4 5 6
11/10 2( 3E) I x 104
Fig. 8. Determination of k 2 by Use of Saturator BypassTechnique. A, raw data; B, raw data correctedby measured (I0 7/I.27), Eq. (8).
-25-
The absolute value of k? can be viewed in two perspectives from a laser
systems point of view. 0 2 (iZ7) is critical to the operation of the cw 07(1&)-1
atom transfer laser since it dissociates 12 with high efficiency. The larger
value of k 2 reported here aids this initiation process and removes I? as a
potential deactivator of I . Eventually, k2 could serve as a pressure-scaling
limitation on the transfer laser since this energy-pooling process is second
order in 02(iA). Note that the "Oz(l Z) catastrophe" observed in the previous
study2 is largely eliminated for discharged 02 by means of the heated satu-
rator and the "saturator-bypass" method. The 'T, catastrophe has been
observed in real time in related experiments;'.- however, for discharged
oxygen, it must have an onset at added 12 pressures greater than 2 mTorr.
C. IODINE-CATALYZED REMOVAL OF Oz(IA)
Derwent and Thrush 7 reported that the measured removal rate of O 2 ('A)
in the presence of I was first order in [O(IA)] and first order in [I]. The
analytic expression for this kinetic behavior was presented as Eqs. (B-5) and
(B-6) in Reference 2.
-dO2 ( 1 A) [ kik6 ](B-6,
dt k + k6 7 ][][02(A)] Ref. 2)
That analysis results in a first-order decay of Oz( iA) given by
L0z( A) J f
*2
R. F. Heidner III, unpublished results.
-26-
The improved experimental procedures described previously were employed
to collect data on the decay of 1. 27- tm and 6340-A emission in the presenceof added I. These data indicate that second-order decay processes in
0 2 (1 A) are not negligible at Oz(iA) and I-atom densities appropriate for atransfer laser device.
The most interesting second-order loss process for 02( A) is the
energy-pooling reaction with I.
k 2
0 o2( A)+ o 02( Z)+ 1 (4)
The collisions that do not result in 02(1Z) must be considered also, e.g.,
!k/
OZ( A) + 1 0 2( Z) + 1 (12)
The decay of 0 2 (IA) monitored by the dimol emission at 6340 A is shown in
Fig. 9. Curvature in the plots is evident although contrary to the prediction
of Eq. (ii). A second discrepancy with theory is that these plots do not
extrapolate well to the intensity at t = 0. Unfortunately, dimol emission is
a poor diagnostic at high 12 addition because of interfering I 2 (B - X) emis-
sion. Thus, the experiments were continued with 0 2 (1 A) fundamental
emission at 1.27 pLm. In changing of diagnostics, considerable sensitivity
to second-order effects is lost because the dimol emission is proportional
to [0 2 (IA)] 2 , and because the dirnol detector (RCA GaAs phototube) is very
stable compared to the intrinsic Ge detector used for . 27-ptn radiation.
Nevertheless, Fig. 10 is a plot of 11. 27 versus time as a function of added
12, with it assumed that first-order kinetics apply. Curvature is not evident
within experimental error; however, the intercepts are not constant, and,therefore, the linearity may be an artifact of the small dynamic range of
-27-
10-9~ =20
9- 2 -
8-~%
x 44*A B b'Lq C
20
__ AOD7619
Aen6340
0 25 50 75 100 125 150 175t, msec
Fig. 9. Time-Dependent 02 A) Dimol and 02()Emission in Presence of 12. 1 + V -72.6 x5 jo-li mol/cm 3 , 02(3L) = 1. 6 x 10mol/cm 3 ; 0(A1 1. 5 x 1to 8 mol/cm3 .
28-
40
Cd,
1098
7
60 2 0 4 0 6 0 8 0 100 120 140t, msec
Fig.10.Time-Dependent Firs t-Order Decay of 02('A)Fi. (X = 1. 27 m) Versus 12, 1 + I* (mol/cm 3 ):
A, 0; B, 4.05 X 10- 1; C, 1. 06 x 10- 10; D,1. 54 x 10- W; EF, 1. 09 x 10-10; F, 2.*10 X 1-0G, 3. 39 x 10- 10;P I-T 4. 38 x f0_1
-29-
0 2 (IA) concentrations measured. If the data are plotted according to Eq. 11),
an empirical first-order removal rate of keff = 1.5 X 1010 cm3/mol-sec is
derived from Fig. it. Derwent and Thrush 7 reported keff = (8.0 ± 1.0)x 1010cm 3 /mol- sec.
When the same data are plotted on the basis of second-order kinetics
(Fig. 1U), the result is extremely interesting. The decay of 0 2 (1 A) is
written as follows:
0z( A) [02(I A)A[?
d dt [02(tA)][I*I = 2(k2 + k')KEQ 3 (13)dt 2 2 EQ [0 ( 3 )
[- [O2 (A)] 0 = 2(k2 + kz)KEQ [I] ] (14)
The intercept variation in Fig. 12 may be within experimental error,
and the linearity is no worse than that in Fig. 10, in which first-order
kinetics is assumed. With the measured value of [0 2 (IA)]5 1 inserted into
Eq. (14), the quantity 2(k + k') :- 1. 3 X 10t cm3/mol-sec is determined(Fig. 13). Given the assumptions involved, this value is rather close to the
value of k? = (5.0 ± 1.0) X 1010 cm 3 /mol-sec, which was determined by acompletely different method. Data over a much larger dynamic range would
be required in order to accurately deconvolute the first- and second-order
components of the decay of 0 A). The results of these studies are
compared with earlier results in Table III.
-30-
5
5 3 0
0 k ef 1.52 x1010CM /mol-sec
2 2
15 mlarr
00 1 2 3 4
1*)+ (111 x 10 10 Mal/cm 3
Fig. If. Determination of keffwith First-OrderDecay of 020A) Assumed
14
10 280 mlorr12
_E
C 1
C14
0= 20466-0 102tme
2-2
IA
141
-12
-I 10
10 0
C 2 8
4- 0
[I]I402 13) x g
Fig. 13. Determination of k2 + k'z with Second-OrderDecay Kinetics Assumred for 0 2('IA)
-33-
-40
0 .0
- 0 -4
13
t4-
- - 00
0* 0
0~~~ '1.00 -
--41
* . 4-w,+ 4)
0 •0 k
a 0
. 0
SIllI
k 4
.44 .0oM
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Lo
IV. DISC USSION
The efficient operation of the cw 02 (iA)-I atom transfer laser requires
a kinetic environment consisting of high concentrations of OZ(IA) and I".
Since I/I must be greater than 0. 5 in order to exhibit laser action, kinetic
studies must distinguish the effects of ground-state and excited-state I atoms.
I to I ratios higher than those used by Derwent and Thrush7 were used in
these studies, which may explain the differences in Table III. Measurements
I 'of the energy-pooling rate k2 between 02( A) and I tend to be low unless
the accelerated decay of 0 2 ( A) by iodine is explicitly accounted for by Eq. (8).
Thus, the present value of (5.0 ± 1. 0) x 1010 cm 3 /mol-sec is strongly
favored over earlier measurements. 2,' 7 Even this value could be systemati-
cally in error if k9 were incorrectly determined. The large value for
k? is supported by the rapid dissociation of injected 12 by 0 2 (1 2-)
Oz( Z ) + 12k 5(3 Z) + 21 (15)
The iodine-catalyzed removal of 0 2 (iA) is a much more complicated
question. The results of the present study support a substantial contribution
to the decay of 0 2 (1 A), which is proportional to [0 2 (IA)]. The following is
a numerical example of the difference between first- and second-order
kinetics. The experimental conditions are typical of the recent laser i experi-
ments; in addition, the I*: and O2(IA) densities are comparable to the present
studie s.
[02( 1 A]o = 1. 5 X 10-8 mol/cm 3 (280 mTorr)
[I] + [i'] = 3.0 x 10-jo mol/cm 3 (6 mTorr)
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[O2(i A)]
[O2(3z)] 0.4
The first-order half-life of O(iA) can be expressed as
= (In Z)(kefI]) " I (16)
= 62 msec (Derwent and Thrush)
= 340 msec (this work)
The second-order half-life of 0 2 (IA) can be expressed as
~1/2 =jZk1 ')I'1- (17)
= Z8. 3 msec (this work)
The predicted second-order half-life for 0(IA) would appear to be the cor-
rect order of magnitude to describe the laser operation. Even the large keff
for first-order decay given by Derwent and Thrush 7 results in a relatively
slow decay. Three scaling cases must be considered:
i. The [0.(IA)]/[0 2 (3Z)] 0 could be increased, which wouldimprove the mass efficiency of the laser but would alsoincrease the decay rate by increasing [ii ] prior to theoptical cavity. Fast, efficient mixing would be imperative.
2. The [O2 (lA)]/[O2 (3 Z)]0 ratio could remain constant, but thetotal O pressure could be increased. The decay rate wouldremain constant if the [I] + [I " ] remained constant.
3. The [I] + [1*1 could be increased to enhance the gain andimprove the energy extraction. This technique could accel-erate the OZ(/A) loss rate to unacceptable levels.
-36-
Gain length scaling may be required rather than [I*] scaling in order to
increase overall system gain. Scaling from [O?(,A)] /[O2)] = 0.4 to
O2(iA)]/[O ) = increases the decay rate of O2(iA) less than a factor
of 2 and should be pursued if technically feasible. Increasing the pressure
of the 0 2 (IA) is very desirable unless the Derwent and Thrush4 value for
k 9 is much lower than the actual value. Experiments on the decay rate of
SO(1 A in pure oxygen system strongly support the Derwent and Thrush
value.
-37-
1
V. CONCLUSIONS
Modification of the Derwent and Thrush3 - 7 kinetic rate package is
necessary because the Oz(A)-I* energy-pooling rate is substantially faster
than these authors have proposed. Furthermore, collisions between O(I A)
and I*", resulting in kinetics that are second order in 0z(IA), may dominate
the removal of OZ(1A) at densities appropriate to the transfer laser. This
area of the kinetics, which includes temperature-dependent measurements,
is of critical importance in accurate laser modeling.
-39-
APPENDIX A
CHEMICAL KINETICS OF THE O2 (1 A)-I ATOM SYSTEMa
I k 1 31+ 2 ( A) -4 1' + 2 . (A-i)
kz
i + Oz( 1A) - I + 2(1 Z ) (A-2)
1 2 31 + Oz( A) - I + 2(3z) (A-Z')
k3
I* a I + h,) (A-3)
0 2 ) O(3Z) + h\) (A-4)
Z37 k 5 OIA
1+ 0 (Z) --- + 2 A) (A-5)
:" + O 2(3Z) --- + O(3Z) (A-6)
i k73 (A- 7)1 +0 2 A) -0 + 0 2( A)
kI: + M . I + M (A-8)
0( A) + 0( 1 A) 2 O*('2-) + 00Th (A-9)
0 2 2;) + wall 0 O( A) + wall (A-10)
a Where possible, the above reactions are numbered as they appear
in Reference 7.
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*kI + wall Ip + wall (A-i11)
.1 k1 12 302 A) + wall 0bO(2 + wall (A -12)
k
14 14
02 ( Z) + o2m 0, 2( A) + 2 (A- 4)
12Z)+ 0 ( Z) + 2 (A- 15)
I17 ) + 0 A) 770+ +z ? + ) (A-17)
k18or I + wall b* 1/21 2 + wall (A -18)
-42-
APPENDIX B
RATE COEFFICIENTS FOR THE KINETIC MODEL OF APPENDIX A
Process k Reference
k ~(4.6 ± 1. 5) X t1 cm 3/mol- sec
10 3k 2 (t. 6 ± 0. 2) X 10 cm /mol- sec 7
(5 t 1) x 10 tocm 3/mol-sec This Work
k + '6 0t cm 3final-sec This Work
k37.8 sec- 2
k40. 077 sec 13 32
k5(1. 6 ± 0. 5) X 101 cm /mol- sec 2
k 6 3.4 x 10 tocm 3/mol- sec 2
k 7 8 x 10 t cm 3/mol-sec 2
k7 3
k91.2 x 10 cm 3/mol-sec 2
k 1 0 0 Yoi x to- 2
kl YH 1 1 2
k 13~
14 34k 151x 10 14cm 3/mol-sec 2
k 1 6 4 x 10 13 cm 3 /mol-sec 2
k 8y 1 8 (Pyrex)- 1; Y18 (Halocarbon)ft 10- 2
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