AD-fi52 734 NEASUREMENT OF FRANCK-CONDON FACTORS FOR THE V'=@ i/PROGRESSION IN THE B-X S.. (U) ARMY BALLISTIC RESEARCHLAB ABERDEEN PROVING GROUND HD W R ANDERSON ET AL.

UNCLASSIFIED DEC 84 BRL-TR-2627 SBI-AD-F388 598 F/G 7/2 NLEIIIIIEIIEII_lllmmlllllllllllomommolESShEEE~E

.1.0

IfII.8

MICROCOPY RESOLUTION TEST CHART

[ , -.. .

AD-A 152 734

[AD

BR TECHNICAL REPORT BRL-TR-2627

LMEASUREMENT OF FRANCK-CONDON FACTORS

FOR THE V'=O PROGRESSION IN

THE B-X SYSTEM OF PO

William R. AndersonSteven W. Bunte r'.,TIC

Anthony J. Kotlar E (LECTE

APR 16 1985

December 1984. B

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED.

L- US ARMY BALLISTIC RESEARCH LABORATORYABERDEEN PROVING GROUND, MARYLAND

.C-,

Destroy this report when it is no longer needed.Do not return it to the originator.

Additional copies of this report may be obtainedfrom the National Technical Information Service,U. S. Department of Commerce, Springfield, Virginia22161.

The findings in this report are not to be construed as an officialDepartment of the Army position, unless so designated by otherauthorized documents.

The use of trade names or manufacturers' names in this reportdoes not constitute indorsement of any commercial product.

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READ INSTRUCTtONSREPORT DOCUMENTATION PAGE IlIFFOIR COMPLETING FORMREPORT NUMf3ER 12, GOVT ACCESSION 1.0.1 -F LIPIENT', CATAL.OG NUMBER

TECHITICAL REPORT BRL-TR-2627 ~ C-7 -_ ____

4 TI', ndStto YPE OF RE1

ORT & PERIOD 70vERED

MEASUREMENT OF FRANCK-CONDON FACTORS FOR THE v'=O FinalPROGRESSION IN THlE B-K SYSTEM OF PO ______________

6 PERFORMING ORG. REPORT N,.-BER

7 AUTHOR(.) 8 CONTRACT OR GRANT NUMBEkI-,

William R. Anderson* Stevenl W. Bunte

Anthony J. Kotlar _______ _________________9PERFORMING ORGANIZATION NAME AND ADDRESS 10 PROGRAM ELEMENT, PROJECT TASK(

AREA & WORK UNIT NUMBEPSZ

UT.S. Army Ballistic Research LaboratoryATTN: AMXBR-IBD 1L161 102AH43Ahordeen Provinjg Ground. MD 210556I I C- )TRr)L~iNG OFFICE NAME AND ADDRESS 12. REPORT DATE

V*. S. Armv BVi II st ic Research Laboratory December 1984A 1-1N: AMIBR-O)- ST rI3 NUMBER OF PAGE_.

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19 SUPPLEMENTARY NOTES

t~~t ~Y~RD1 (C,,tnm~ onrev~erse side if necessary tnd Identify by block num~ber)

1,aser Excited FluorescenceFranck-Condon FactorsOrganophosphonate Esters

20 ABSTRACT (CComtim e a nereff eid It nseIean~d IdertiIfFr bF block number) gkl

Laser Fluorescence of P0 produced in a microwave discharge throughorganophosphonate esters has been studied. The fluorescence was pumped inthe Bi do~uhlet sigma plus - X doublet pi 3250 Angstrom system. RelativeIntensities of fluorescence for the v prime equals zero progression were

* measurod. These intensities were used to derive Franck-Condon factors forthe v prime equals zero progression.

DD , 14n EDOTION OF I'NOY W5IS OBSOL E TE UNCLASS IFIED

SE CURITY CL ASSI FIC ATICON f THIS P A F When tV0'" F'

TABLE OF CONTENTS

PAGE

[. [NTROI)UCTION .. ............ ...... 5

It. EXPERIMENTAL ............ . ..... .......... .... ....... .. . ...... o6

[it. RESULTS AND DISCUSSION. . . .. .. ... . . .o.o. ......... . ... ... 6

tV. CONCLUSIONS ............................ o ......... .18

ACKNOWLEDGEMENTS......... .... o.o.. .. ... . ... . ........ .......... .19

REFERENCES ..... .... ............. . .. . ... * ................ 20

I)[STRIBu'rION LIST.. ...... . ... ....... . .o.. * ....... ...... 23

A,, 1• 1•85

... ~~ ~ A r16.. ., 1'. "8'".

I. INTRODUCTION

Electronic spectra of the PO radical have been known and studied for over

50 years.' Studies of the transition between the two lowest-lTing electronic

states, the B2 Z+ + X2 11 3250A system, have concerned rotational -5 andvibrational3'4 analyses and B state perturbations. 3'5 More recentInvestigations have reported the laser excited fluorescence (LEF)6 and

multphoton ionization spectra.7 ,8 Our interest in this radical results fromits involvement in several possible fragmentation detection schemes for nerveagents since their chemical structure is centered around a PO double bond. Inthe present work, LEF of the B-X system was further studied. A more detailed

account of the procedures and results is given than has previouslyappeared. 9 The PO was produced in a microwave discharge through two chemicals

lReferences to earliest work may be found in Spectroscopic Data,

Heteronuclear Diatomic Molecules, Vol. 1, ed. S.N. Suchard, IFl/Plenum DataCompany, NY, 1975. A compilation of papers from 1955 to 1979 is availablein K.P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure,

IV. Constants of Diatomic Molecules, Van Nostrand Reinhold, Co., NY, 1979.

2 N.L. Singh, "Rotational Analysis of the Bands of Phosphorus Monoxide,"

Can. J. Phys., Vol. 37, p. 136, 1959.

3 aR.D. Verma and S.R. Singhal, "New Results on the B2 +, b4 - and X2 States

of PO," Can. J. Phys., Vol. 53, p.411, 1975.

hS.R. Singhal, "High Resolution Study of the Spectral Region 3000A - 3900A of

the PO Molecule," Ph. D. Thesis, University of New Brunswick, Fredericton,

New Brunswick, Canada, 1973.

4 C. Couet, N. Tuan Anh, B. Coquart and H. Guenebaut, "Contribution A L'EtudeDes Systemes Electroniques du Radical PO. 3e Partie: Le Systeme 8(transition B2E+ - X2mr), .1. Chim. Phys., Vol. 65, p. 217, 1968.

5aS.R. Rai, D.K. Ral, and K.N. Upadhya, "Analysis of Some Bands of the 0

System of PO, 1. Phys. B: Atom. Molec. Phys., Vol. 5, p. 1038, 1972.

bS.B. Rai, B.R. Yadav, and D.K. Ral, "Perturbations in the B2 E+ State of PO,"

J. Chim. Phys., Vol. 73, p. 905, 1976.

6 M.A.A. Clyne and M.C. Heaven, "Laser-Induced Fluorescence of the PORadical," Chem. Phys., Vol. 58, p. 145, 1981.

7K.C. Smyth and W.G. Mallard, "Two-Photon Ionization Processes of PO in aCH 2 /Air Flame," .1. Chem. Phys., Vol. 77, p. 1779, 1982.

4 J.S. Chou, D. Sumtda, and C. Wittig, "2-Frequency 2-Photon Ionization ofNascent PO (X2 r) from the Collision Free IR Photolysis of Dimethyl-

Methytphosphonate," Chem. Phys. Lett., Vol. 100, p. 397, 1983.

9 W.R. Anderson, S.W. Bunte, and A.J. Kotlar, "Laser-Excited Fluorescence of1'0 from Organophosphonate Esters," Conference on Lasers and Electro-Optics83, Paper THD4, Baltimore, MD, May 1983.

5

structurally similar to nerve agents, either dimethyl-methylphosphonate [DMMP,(Ci30) 2(P=O)CH3I or its ethyl substituted analog, diethyl-ethylphosphonate

(DEEP) which yielded comparable results. Excitation scans of the (0,0) bandof the B-X system were obtained, similar to previous results.0 In addition,relative fluorescence intensity measurements were made for the vibrationalprogression emitted from the v'=O excited level. Franck-Condon factors (FCFs)derived from these measurements are compared with values calculated from theRKR potentials. Though the nerve agents are violently poisonous, the

I simulants are only mildly toxic.* In fact, it is suggested that the simulantsare safer and much more easily handled than the poisonous PO precursors used

in previous studies.2 - 6

I1. EXPERIMENTAL

PO was produced by flowing about 7 x 10- 2 torr of DMMP or DEEP in about Itorr of argon diluent through a 2450 MlHz microwave discharge. The PO was

excited downstream from the discharge in a stainless steel cell usingradiation in the 3250A region from a flashlamp pumpyd, tunable dye laser(Chromatix CMX-4). The laser linewidth was 0.3 cm- FWHM. Typical pulseenergies were -4.2 mJ with pulse duration - I psec. Fluorescence was detectedusing either a monochromator with photomultiplier tube or a photomultipliertube with a visible cutoff filter. A small portion of the laser radiation wassampled by a reference photodiode prior to its entry into the fluorescencecell. Signals from the photomultiplier and power reference photodiode wereprocessed, and their ratio was taken in a boxcar averager. Hard copy wasobtained using a chart recorder or computer.

All of the figures and quantitative measurements presented hereininvolved DMJP as the precursor. However, as previously stated, qualitativelysimilar spectra were obtained using DEEP. Though careful quantitative studieswere not performed using DEEP, the intensities of PO fluorescence from the twoprecursors were comparable indicating similar yields of PO for each.

Ill. RESULTS AND DISCUSSION

(0,0) Band Excitation Scans

The spectrum of PO was first identified by running excitation scansthrough the (v', v") = (0,0) region of the B-X system and comparing results tothe previously measured emission2 ,3a and LEF6 spectra. Since the spin-orbitconstant of the X state is quite large (224 cm- ),2- 4 a large spectralsplitting of the subbands from the 2 H ground state is observed. Scans of both

the 1/2and B2 + / subbands are shown in Figure 1. Thespectrum was obtained by scanning the laser wavelength while the monochromatorremained fixed at 3250A with a bandpass of 33A FWHM. This handpassencompassed nearly the entire (0,0) region so that results using themonochromator-photomultiplfer vs filter-photomultiplier combinations werealmost identical.

*Of course, one shoild not go out of one's way to ingest or breathe the

si: mlants.

6- ',a I : Jz - . . .,- t - . ._ _ - "" -- "" " . . ,

I

kI

OP37 '3 2 9 25 21 17

I

3276 A 3274 A

4

Figure Ia. A Laser Excitation Scan Through The (0,0) Band Of The82E + + X211 System Of PO. Triangles On The Wavelength Scale

Indicate Laser Etalon Reset Positions, An Artifact Of The TuningMechanism. A. The B2£ + X f3/ 2 Subband.Wavelengths In Angstroms. (Continued)

7

I

LrriI jjl I I

Ii15 k3 I'! 9 7~I

10

pai, pI k I

W I}'!I rI :1 hh,

A 3271 A. 3269

S8Figure La. Laser Excitation Scan Through The (0,0) Band Of The

B2 E+ + X'ir System Of P. Triangles On The Wavelength Scale

Indicate Laser Etalon Reset Posi~ions, bn Artifact Of The TuningMechanism. A. The B £+ +. K 3/2 Subband.

Wavelengths In Angstroas. (Continued)

iB

0

. - *•...-*, .*, - * .

p22 9 911 13 15

-~ R,

2 10 20 30

I \ ; ', '

( II

' , , I '

A3267

Figure la. A Laser Excitation Scan Through The (0,0) Band Of The

B2 E + X2w System Of PO. Triangles On The Wavelength Scale

Indicate Laser Etalon Reset Positions, An Artifact Of The Tuning

Mechanism. A. The B2E + + X2 W3/ 2 Subband.

Wavelengths In Angstroms. (Continued)

9

6

R217 21 25 29 ' 33

3264 A 2262 260 A

Figure la. A Laser Excitation Scan Through The (0,0) Band Of The

B2 + + X2 f System Of PO. Triangles On The Wavelength Scale

Indicate Laser Etalon Reset Pos tions, An Artifact Of The TuningMechanism. A. The B E+ + X w 3/2 Subband.

Wavelengths In Angstroms.

100L

-.4

5 27 25 19 15 II

I !I

132,51 3249

Figure lb. A Laser Excitation Scan Through The (0,0) Band Of The+ X2 System Of PO. Triangles On The Wavelength

Scale Indicate Laser Etalon Reset Positions, An Artifact Of TheTuning Mechanism. B. The B2E + + K2 1/ 2 Subband.

Wavelengths In Angstroms. The Q, Branch, From N"=6 To The Head,

Was Recorded At A Sensitivity About Two Times Lower Than

The Rest Of The Subband. (Continued)

S

11

0

21 H 6 R+RG I

F, 6-~ 0 1i0 17

V4 I it

3247 A3245A

Figure b. A Llser Excitation Scan Through The (0.0) Band Of The

AB +~ Y v System Of P0. Triangles on The Wavelength

"o i i' nAt if a

Scale Indicate Laser Etalon Reset ost ions, AnAtiat Of The

Tuning Mechanism. B. The . Subband.

Wavelengths in Angstroms. The 01 Branch, From N"=6 To The Head,

Was Recorded At A Sensitivity About Two Times Lower Than

4 The Rest of The Subband. (Continued)

12

4

S, , , ,'1 . . S . - R 2 1

17 30 34IR 21

32142

* I

2 E+ + isytmO P.TinlsonTeWvlnt

131

+ 1

CI ,

,/ ,K ., FA . '., ,', ,"I. ,. ' ,,?," , i.,,, ,/4 .K .u . I ' ,

A[ ,242 A,

I

K

Figure1 lb ALaser Excttion Scan Through The (0,0) Band Of The+X i System Of P0. Triangles On The Wavelength

Scale Tndicate Laser Etalon Reset P~sttons, An Artifact Of TheTuning Mechanism. B. The B2E + + X21r1/2 Subband.

Wavelengths In Angstroms. The Q1 Branch, From N"=6 To The Head,

*I Was Recorded At A Sensitivity About Two Times Lower Than

The Rest Of The Subband.

'+ 13

6

The earlier work on PO contains a discreyacy as to the rotationalnumbering of the P1 branch in the (0,0 band.= '' For this reason, themeasured line positions were refitted using a weighted nonlinear leastsquares routine and standard doublet Hamiltonian.1 I The results indicate theoriginal P1 branch assignments

2 ,3 b were correct.* Therefore, the rotationalassignments in Refs. 2, 3b should be retained. The assignments of the PIbranch in Figure 1, Reference 3a and Figure 2, Reference 6 should be increasedby one unit.** The correct assignments are shown in our Figure lb.

The fitting of the band has led to predicted bandhead positions and thecorresponding values of J" at which they occur. The J" values at which thevarious branches turn have not appeared previously because of the difficultyin resolving this very dense region of the spectrum. The i' value at whichthe branches reverse and the calculated wavelength of the appropriatetransition are given in Table I. The observed bandheads from Reference 3a arealso given for comparison.

Franck-Condon Factors for v'=0

For the measurement of FCFs, the laser wavelength was fixed on thestrongest feature of the excitation spectrum, the Ql + QP21 bandhead (seeFigure 1 and Table 1). The monochromator was then scanned to obtain relative

* intensities of the vibrational bands originating from v'=O. Signals were*obtained for v"=O, 1, and 2, but not for v"=3. Since the FCFs are expected to

lOaA..T. Kotlar, "An Evaluation of the PO (0,0) B2 E+ - X2 rr Spectroscopic

Parameters for Diagnostic Applications," Chemical Research and DevelopmentCenter Scientific Conference on Chemical Defense Research, Aberdeen ProvingGround. MD, November 1983.

bA.J. Kotlar, BRL Report to be published.

*1A.J. Kotlar, R.W. Field, J.1. Steinfeld, and J.A. Coxon, "Analysis ofPerturbations in the A2'i - X2 E+ 'Red' System of CN," J. Mol. Spectrosc.,

Vol. 80, p. 86, 1980.

*The discrepancy apparently arose from an accidental mislabeling of the P1branch in Figure 1 of Reference 3a. Cross checks of our result byM. Heaven 12 and R.D. Verma1 3 were in agreement.

12 M. Heaven, private communication.

13 R.D. Verma, private communication.

•* Some confusion could result because in the text of Reference 6, the authors

state that the P1 branch assignments of Singh2 must be increased by one

unit. However, in their Figure 2 of Reference 6, as in the similar FigureI of Reference 3a, the numbering is lowered by one unit. Therefore, we doindeed mean the numbering in their figure must be increased by one unit.It should be noted that the rotational assignments given in tabular form bySinghal3 b are in excellent agreement with those of Singh.

14

Table 1. Bandhead Positions in the (0,0) Band of the B-X System of POa

Wavelength (A) Assignment

Observed Calculated

3246.1 3246.2 Q1 (27.5)

3246.2 QP2 1 (27.5)

3270.4 3270.4 P2 (44.5)

3270.5 PQ12 (45.5)

a - Observed values were taken from Reference 3a.

decrease for higher v", higher values were not checked. Magnitudes of the

signal levels observed for v"=O and 2 necessitated usage of different voltages(an uncalibrated gain change) on the photomuliplier. Therefore, the bandintensity ratios were obtained in pairs with the (0,0):(0,1) ratio at low andthe (0,1):(0,2) ratio at high sensitivity. At least four scans were obtainedfor each band at the necessary sensitivities. A representative pair of bandsis shown in Figure 2. Areas under these curves were obtained by computer

integration (trapezoidal summation) and averaged for the four runs. The areaunder the (0,0) bands was then corrected for a small amount of laser scatterfrom the cell walls and windows whose magnitude was obtained from runs withthe microwave discharge off (see Figure 2). Finally, the combined lensing,

monochromator-photomultiplier system's spectral sensitivity was calibratedusing an NBS traceable tungsten standards lamp. The ratios of Einstein band

emission coefficients thus obtained were AO 1 : AO 0 = 0.0690 ± 0.0073 andAO,2: AO0 4 0.0824 ± 0.0119. These ratios may be used irrespective of any

assumpt'ons about the electronic transition moment. If one assumes theelectronic transition moment is constant over the range of internuclear

distance sampled in the three vibrational hands, then by doing the appropriatealgebraic manipulations, FCFs may be derived from these Einstein coefficient

ratios. These are shown in Table 2.

Table 2. Measured and Calculated Franck-Condon Factors for the v'=0Progression in the B-X System of PO. The electronic transition

moment was assumed constant in the derivation of FCFs from

experimental data (see text).

S(v' v) qv', v', (meas.) v.. (RKR calc.)

(0,0) 0.9213 * 0.0071 0.9776

(0,1) 0.0720 ± 0.0076 0.0194

(0,2) 0.0067 ± 0.0012 0.0028

(0,3) Not detected 0.0001

15

.;v ~ .- , (~-- . .--

(0,0)GA IN I

.!.1

LASER SCATTER

3296 3216

4

j,. ,.,(0,1)

~ GAIN 708

3421 3391 3361

Figure 2. Fluorescence Scans Of The (0,0) And (0,1) Vibrational Bands.Wavelengths In Angstroms. Note That The Baseline For The

Laser Scatter Scan Is Displaced Upwards From That For6 The Scan Of The (0,0) Band. The Scattering Correction

To The (0,0) Intensity Is Actually Quite Small.

16

I :" .

FCFs were also obtained from theoretical calculations for the entire v',v array using the RKR potentials. Subsequent to these calculations, it wasdiscovered that similar calculations had been peyformed previously bySinghal and concurrently by Smyth and Mallard. All of these results are inexcellent quantitative agreement for the v'=O progression. The present

theoretical results for the v'=O progression are shown in Table 2 forcomparison with the experimental results. Note that though the qualitativetrends are quite similar, the quantitative agreement is poor, especially forthe small FCFs. Small FCFs are especially difficult to calculate because theyresult from the cancellation of many positive and negative contributions inthe integration of the vibrational wavefunctions; that is, they resultessentially from the difference of two large, nearly equal numbers. Suchproblems have been suggested previously as the cause of a several orders ofmagnitude difference in measured and calculated FCFs in the A-X system ofNH." Along these lines it is also worth noting that Smyth and Mallard state7

that their multiphoton ionization results could perhaps be better explained ifthe RKR calculational procedure underestimates several of the smaller FCFs.Unfortunately, the sketchy data presently available do not allow one to becertain whether problems with the FCF calculations or changes in theelectronic transition moment with internuclear distance, as is known to occur

in the A-X system of OH, 15 are responsible for the poor agreement in Table2. In any event, the Einstein emission coefficient ratios may he usedirrespective of any assumptions about the form of the transition moment. Themeasured Einstein coefficients are to be preferred over those calculated from

the theoretical FCFs, especially for rotational quanta near N'=27 (turningpoint of the Q1 bandhead) where the measurements were performed.

Concentration of PO

A rough estimate of the density of PO in the excitation region wasobtained using a procedure entirely analogous to that used previously for C2and CN, and NCO in a flame with changes appropriate to the tunable, pulsedlaser. In the present work, the absolute fluorescence intensity in the (0,0)hand was directly measured rather than referenced to N2 Raman signals as was

14 W.R. Anderson and D.R. Crosley, "Laser-Excited Fluorescence in the A-X

System of NH," Chem. Phys. Lett., Vol. 62, p. 275, 1979.

15aD.R. Crosley and R.K. Lengel, "Relative Transition Probabilities and the

Electronic Transition Moment in the A-X System of OH," J. Quant. Spectrosc.Radiat. Transfer, Vol. 15, p. 579, 1975.

hD.R. Crosley and R.K. Lengel, "Relative Transition Probabilities in the A-X

System of OD," J. Quant. Spectrosc. Radiat. Transfer, Vol. 17, p. 59, 1977.

16 1.A. Vanderhoff, R.A. Beyer, A.J. Kotlar, and W.R. Anderson, "Ar+ Laser-Excited Fluorescence of C2 and CN Produced in a Flame," Combust. Flame,Vol. 49, p. 197, 1983.

1 7W.R. Anderson, J.A. Vanderhoff, A.J. Kotlar, M.A. DeWilde, and R.A. Beyer,"Intracavity Laser Excitation of NCO Fluorescence in an AtmosphericPressure Flame," J. Chem. Phys., Vol. 77, p. 1677, 1982.

17

-"4 ' - - " -- . . ." ; , i . : ' ' ' .

done previously. The Einstein coefficients were obtained using the B statelifetime, 250 nsec, measured in Reference 6 and the measured FCFs.

Linestrengths necessary for the calculation of absorption coeffic ents for theresolved rotational lines were obtained using formulae of Earls. 18 The

pumping transition(s) was assumed to be Doppler broadened at 400 K, atemperature typical of our flow system. The measurement was made by pumping

in the Q, bandhead where the laser line overlaps several rotational lines ofPO. To estimate the effective number of transitions pumped, the relativeintensities of RI(27) and the Q, handhead, which occurs near N"=27, wereobtained from the excitation scan. After correcting for rotationallinestrengths, it was found that the laser effectively overlaps 6.9transitions.* Finally, the importance of quenching was ascertained. It isexpected that the quench rate of B state PO by Ar is certainly less than thatof N9 measured in the previous LEF study 6 and found to be gas kinetic. Now,in comparing the Einstein emission coefficients, Aviv.., to the quench rate, Q,for N2 at I torr, it is found that the radiative and quench rates are nearlyequal. Saturation checks were run using the ratioing boxcar averager so thatstimulated emission is known to be unimportant. The fluorescence rate under

these conditions is proportional to A,v/[(E.. Av, ") + Q ] rather than AvIv,./Qas in Eq. (3) of Reference 16. The quench rate actually used was that ofN2. However, if the quench rate of Ar is much less than for N2 , the effectwould reduce the estimated PO density by only a factor of about 2. The

density estimated in this manner was about 1 x 1010 cm- 3 . Thus, about 1 x10-5 of the phosphorus was present as PO. Because of the variousuncertainties involved in these estimates, they are believed to be good onlyto within a factor of t0.**

IV. CONCLUSIONS

In these experiments, PO was obtained for fluorescence ;tudies usingorganophosphonate esters as precursors. Discovery of these sources should aidin further research on PO as they are more easily handled than earlierprecursors. The measurement of FCFs, together with the previous lifetimemeasurements, now makes quantitative determination of PO using absorption orfluorescence techniques possible.

18 L.T. Earls, "Intensities in 2T - 2Z Transitions in Diatomic Molecules,"

Physical Review, Vol. 48, p. 423, 1935.

*This procedure is valid because the Boltzmann fractions and normalizedrotational linestrengths, and, hence, Einstein coefficients, do not varysignificantly around N"=27. The result is similar to that obtained by

dividing the laser linewidth, 0.3 cm 1, by the density of lines in theregion of the Q, bandhead.

**This uncertainty limit could have been reduced to about a factor of 2.5,even in the absence of further quench rate Information, if a more carefullaser power measurement had been available at the time of the experiment.The result shows that good quantitative measurements of Pt1 could he madeeven in the absence of very precise quench rate tnformation.

18

:" ""6" "" " " " '' ++ : :+

ACKNOWLEDGEMENTS

-. The authors extend their gratitude to Dr. M. Heaven and Dr. R.D. Verma- for discussions of spectral assignments and to Dr. Verma for sending

tabulated line positions used in early analysis of spectral data. Gratitudeis also extended to Dr. Dennis Flanigan of the Chemical Research andDevelopment Center for providing the organophosphonate esters used in thisstudy. This study was performed under internal funds of the BallisticResearch Laboratory.

r

S

19

,.. - 'I - ..... ..

REFERENCES

1. References to earliest work may be found in Spectroscopic Data,

Heteronuclear Diatomic Molecules, Vol. 1, ed. S.N. Suchard, IFI/PlenumData Company, NY, 1975. A compilation of papers from 1955 to 1979 is

available in K.P. Huber and G. Herzberg,, Molecular Spectra and Molecular

Structure, IV. Constants of Diatomic Molecules, Van Nostrand Reinhold,

Co., NY, 1979.

2. N.L. Singh, "Rotational Analysis of the S Bands of Phosphorus

Monoxide," Can. J. Phys., Vol. 37, p. 136, 1959.

3a. R.D. Verma and S.R. Singhal, "New Results on the B2 + , b4 C and X2 1

States of PO,- Can. J. Phys., Vol. 53, p.411, 1975.

h. S.R. Singhal, "High Resolution Study of the Spectral Region

3000A - 3900A of the P0 Molecule," Ph.D. Thesis, University of New

Brunswick, Fredericton, New Brunswick, Canada, 1973.

4. C. Couet, N. Tuan Anh, B. Coquart and H. Guenebaut, "Contribution A

L'Etude Des Systemes Electroniques du Radical P0. 3e Partie: Le

Systeme a (transition B2 E+ - X.1), 1. Chim. Phys., Vol. 65, p. 217,

1968.

5a. S.B. Rai, D.K. Rai, and K.N. Upadhya, "Analysis of Some Bands of the 5System of PO," J. Phys. B: Atom. Molec. Phys., Vol. 5, p. 1038, 1972.

b. S.B. Rai, B.R. Yadav, and D.K. Rai, "Perturbations in the B2 E+ State of

PO,- T. Chim. Phys., Vol. 73, p. 905, 1976.

6. M.A.A. Clyne and M.C. Heaven, "Laser-Induced Fluorescence of the PO

Radical," Chem. Phys., Vol. 58, p. 145, 1981.

7. K.C. Smyth and W.G. Mallard, "Two-Photon Ionization Processes of PO in a

C2 H2 /Air Flame," J. Chem. Phys., Vol. 77, p. 1779, 1982.

8. .J.S. Chou, D. Sumida, and C. Wittig, "2-Frequency 2-Photon Ionization ofNascent PO (X211) from the Collision Free IR Photolysis of Dimethyl-

Methylphosphonate," Chem. Phys. Lett.. Vol. 100, p. 397, 1983.

9. W.R. Anderson, S.W. Bunte, and A.J. Kotlar, "Laser-Excited Fluorescenceof PO from Organophosphonate Esters," Conference on Lasers and Electro-

Optics 83, Paper THD4, Baltimore, MD, May 1983.

lOa. A.I. Kotlar, "An Evaluation of the P0 (0,0) B2E + - X2 1ir SpectroscopicParameters for Diagnostic Applications," Chemical Research andDevelopment Center Scientific Conference on Chemical Defense Research,

Aberdeen Proving Ground, MD, November 1983.

b. A.J. Kotlar, BRL Report, to be published.

II. .J. Kotlar, R.W. Field J.I Steinfeld, and T.A. Coxon, "Analysis ofPerturbations in the A2i1 - XI 'Red' System of CN," J. Mol. Spectrosc.,

Vol. 80, p. 86, 1980.

20

I

12. M. Heaven, private communication.

13. R.D. Verma, private communication.

14. W.R. Anderson and D.R. Crosley, "Laser-Excited Fluorescence in the A-XSystem of NH," Chem. Phys. Lett., Vol. 62, p. 275, 1979.

15a. ).R. Crosley and R.K. Lengel, "Relative Transition Probabilities and theEIectronic Transition Moment in the A-X System of OH," J. Quant.spoctrosc. Radiat. Transfer, Vol. 15, p. 579, 1975.

h. D.R. Crosley and R.K. Lengel, "Relative Transition Probabilities in theA-X System of 01)," J. Quant. Spectrosc. Radiat. Transfer, Vol. 17,p. 59, 1977.

It. [.A. Vanderhoff, R.A. Beyer, A.J. Kotlar, and W.R. Anderson, "Ar+ Laser-

E1k-fted Fluorescence of C2 and CN Produced in a Flame," Combust. Flame,Vol. 49, p. 197, 1983.

17. W.R. Anderson, .J.A. Vanderhoff, A.J. Kotlar, M.A. DeWilde, andR.A. Beyer, "Intracavity Laser Excitation of NCO Fluorescence in anAtmospheric Pressure Plame," J. Chem. Phys., Vol. 77, p. 1677, 1982.

18. L.T. Earls, "Intensities in 211- 2E Transitions in Diatomic Molecules,"Physical Review, Vol. 48, p. 423, 1935.

21

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