c.i. frum et al- fourier transform emission spectroscopy of the a'^3-pi-x^3-sigma^- transition of...

8/2/2019 C.I. Frum et al- Fourier Transform Emission Spectroscopy of the A'^3-Pi-X^3-Sigma^- Transition of PtO

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JOURN AL OF MO LECULAR SPECTROSC OPY 150,566-575 (199 I)

Fourier Transform Emission Spectroscopy of theA311-X 3E - Transition of PtO

C. I. FRUM, R. ENGLEMAN, JR., AND P. F. BERNATH~,~Department of Chemistry, The University of Arizona, Tucson, Arizona 85721

A new II electronic state of PtO has been observed between 7100 and 8015 cm- above theground state. Three independent electronic systems connecting R = O+, 1, and 2 in the upperstate to V = 1 in the ground state have been recorded in emission from a Pt hollow cathode withthe Fourier transform spectrometer associated with the McMath solar telescope at Kitt Peak. Weinterpret hese three transitions as arising from the spin components ofa new AII-XZ- transitionin Hunds case (a) notation. Molecular constants (including 62doubling parameters) for the newelectronic state have been determined from the analysis of the data. o 1991 Academic press, IX.

INTRODUCTIONThe emission spectrum of PtO has been previously recorded in the ultraviolet and

visible region of the spectrum by several workers ( Z-4). The first two electronic systems,the AZ+-XZ+ (I) and DZ+-XZ+ (2), were analyzed as Z+-lZ+ transitionsassuming a singlet state as the ground state for the molecule. In a matrix isolationinvestigation of PtO and Pt2, Jansson and Scullman (5) observed several transitionsassigned to PtO between 2500 and 9000 A but none of them matched the previouslymeasured A-X and D-X systems. The origin of this discrepancy is not clear. A fewyears later, Sassenburg and Scullman (3, 4) discovered additional emission bands ofPtO. All these new transitions had the previously known X Z+ state or a new statewhich they designated as the x state as the lower state. The new x state had the characterof an Q = 1 state and was 945.929 cm- above the X state. It was evident (3) that theground state of PtO has 32--symmetry and that the X and x states are in fact the D= 1 and 0 + spin components which originate from a 2 - state in Hunds case ( c ) couplingscheme (6).

We report here the discovery of a new 311electronic state of PtO about 7600 cm-above the ground state. The emission spectra analyzed here support the assumptionthat the ground state of PtO is a Z- state.

EXPERIMENTAL DETAILSThe new electronic transition of PtO was recorded in emission with the Fourier

transform spectrometer associated with the McMath solar telescope at Kitt Peak. Theinstrument was operated with a CaF2 beamsplitter and InSb detectors. The spectral

Current address: Department of Chemistry, University of New Mexico, Albuquerque, NM 87 131.2Also: Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada N2L 3G 1.3Camille and Henry Dreyfus Teacher-Scholar.OO22-2852191 3.00Copyright Q 1991 by Academic Fres, Inc.AU rights of repr oduction in any form r eserved.

566


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EMISSION SPECTRUM OF PtO 567band pass was 1850 to 9000 cm- with a resolution of 0.02 cm-. Eight consecutivescans were coadded for a total integration time of 40 min to increase the signal-to-noise ratio. However, the signal-to-noise was relatively poor ranging from 10 for thestrongest system to less than 3 for the weakest electronic transition.

Gaseous PtO was produced in a hollow cathode discharge lamp. The cathode wasmade of oxygen-free Cu with a platinum tube insert. A mixture of Ne and Oz flowedat a slow rate through the cathode during the experiment. The total pressure was 3.2Tot-r of which 0.4 Torr was Oz. At this pressure a discharge current of 190 mA yieldeda stable discharge.

The strong Ne atomic lines present in the spectrum were used to provide the wavenumber calibration. The spectrum was calibrated to better than f0.001 cm- withthe Ne line positions measured by Palmer and Engleman ( 7).

RESULTS AND ANALYSISPC-DECOMP, a spectral analysis program developed by J. W. Brault of the National

Solar Observatory, was used for data reduction.Three independent electronic systems each having only one strong vibrational band

were identified between 7 100 and 80 15 cm- . An energy level diagram of the observedtransitions is shown in Fig. 1. These are found to be the transitions from the Q com-ponents of an excited state of 311 ymmetry to the Q = 1component of the 3L: groundstate of PtO. The three states which originate from a Hunds case (c) 311state with Q= 0, I,2 are designated as Of, 1, and 2 (the O- state was not observed). All individualbranches were picked out using an interactive color Loomis-Wood program runningon a 486133 microcomputer.

0'FIG. 1. Energy level diagram of the observed A%XZ- electronic system of the PtO molecule. The

energy levels are not drawn to scale.


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568 FRUM, ENGLEMAN, AND BERNATH

7160 7180 7200 7220 7240 7260FIG. 2. The A311-X3B- transition of PtO. The 0+-x1 system is shown here. Many low J lines are

missing in all three branches.

Platinum has six naturally occurring isotopes, 190Pt, .01%; 92Pt,0.79%, 94Pt, 32.9%;95Pt, 33.8%; Pt, 25.3%. The isotope splitting caused by the three major isotopes( L94Pt, Pt, and 196Pt) was observed at high J in the 0+-x 1 and the 2-x 1 systems.However, the intensity of these lines was so poor that we refrained from fitting eachisotopomer independently.

The electronic system lying at the lowest wavenumber was the most intense. Onlyone vibrational band was found in this region, as shown in Fig. 2. This band showeda strong Q branch and two weaker P and R branches of almost equal intensity asexpected for a transition with ASI = +l and one D = 0 state. The spectrum wasassigned to the 0+-x1 electronic transition of PtO. The rotational levels of the O+state have all e parity while the levels in the 1 state are split into e and fparity levelsby Q-type doubling. The spectrum was weak so the rotational assignment was com-plicated by the large number of missing low Jlines. Fortunately, the assignment couldbe carried out using a least-squares fitting program and a fast computer. We startedwith an initial guess and then shifted the assignment simultaneously in all threebranches to minimize the variance of the fit. As a final test for the validity of the

31 28 2.5 Q(J)I53 So 47 R(J)18 1 I - 14 12 P(J)

J II - n * * 0 ) /_, 7215 7220

FIG. 3 A. portion of the O-O band of the 0+-x 1 system.


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EMISSION SPECTRUM OF PtO 569assignment we predicted the R head from the molecular constants obtained and foundgood agreement with the measured value of 724 1.262 cm-. The molecular constantsof the lower state were found to be identical (within experimental error) with thevalues for the x 1, v = 0 tate as determined by Sassenberg and Scullman (3, 4) fromtheir analysis of several emission spectra attributed to PtO. The observed band wastherefore assigned to the O-O band, which seemed the most reasonable choice on thebasis of the Franck-Condon principle. A portion of this band is shown in Fig. 3 andthe determined molecular constants are presented in Table I. The line positions andthe differences between the observed and calculated values are shown in Table II.

The assignment for the other two systems was even more complicated due to lowerintensity of the transitions. Each system showed only one vibrational band. The strongersystem centered around 7999 cm- (see Fig. 4) showed six distinct branches: two Qbranches, two R, nd two P branches with two R heads at 8011.598 and 8012.703cm-. The Q branches were almost 10 times stronger than R and P branches whichshowed almost equal intensity. The transition was assigned as the 2-x 1 system of PtO(see Fig. 5 ). In a 2 state the O-doubling of the rotational levels also occurs but thesplitting is smaller since the interaction is of second order. The rotational assignmentwas carried out in a manner similar to that for the 0+-x1 system. Fortunately, wewere able to fix the ground constants to the values previously obtained, greatly facil-itating the assignment. However, the large number of missing lines in the spectrumrequired multiple shifts until all six branches fitted together and the variance of theoverall fit was a minimum. Finally, both the upper and lower state constants werevaried in the least-squares fit. As expected, the molecular constants obtained in thisway did not change significantly from the values obtained in the fit with fixed lowerstate constants. The values obtained for the molecular constants of the lower state ofthis transition confirm the assignment to the v = 0 level of the xl state. The best

TABLE IMolecular Constants Obtained from the Least-Squares Fit of the AII-X3X

Electronic Transition of PtO

State T B D 9 90/lO /10-j /lo8

xl 0.3783383(41) 0X39(26) 099127(u)) 0.339(15)0 7234.53284(13) 0.358&X6(40) 0.3277(19) -1 7861.89992(15) 0X265532(27) 0.15285(11) 0.23902(27) 0.1273(15)2 7999.42805(11) 0X74%38(16) 0..355370(41) - 0.1630(29)

Note. The values are given in inverse centimeters with one standard deviation enclosed in parentheses.a From the 0+-x 1 transition. For the l-x 1 and 2-x 1 fits these constants were held fixed.


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5 7 0 FRUM, ENGLEMAN, AND BERNATHTABLE II

Line Positions of the O-O Band of the 0+-x1 Electronic Transition of PtO

J Q(J) o-c P(J) o-c R(J) o-c

S6769

10111213141s161718192021222324252627282930313233343s3637383940414243444546474849505152535455565758596061

7232.0001 -47231.5387 -137231.0400 -127230.5025 -137229.9297 167229.3121 -197220.6627 147227.9678 -257227.2395 -137226.4732 37223.6662 -37224.8215 -17223.9384 27223.0169 67222.0559 17221.0574 5722O.OlB4 17218.9410 -237217.8279 -87216.6759 57215.4846 107214.2526 -67212.9827 -137211.6765 27210.3298 07200.9455 -17207.5210 27206.0580 -27204.5573 47203.0163 -47201.4374 -47199.8200 -17198.1641 67196.4669 -127194.7348 107192.9601 -57191.1483 -17189.2975 37187.4069 -27105.4784 4

7230.3342 -707229.3912 917228.3882 597227.3456 327226.2622 07225.1413 -47223.9867 587222.7761 -367221.5356 -277220.2515 -517218.9410 647217.5725 27216.1668 -297214.7231 -367213.2419 -177211.7166 -347210.154s -137208.5500 -207206.9078 37205.2210 -177 2 0 3 . 4 9 6 8 -77201.7327 77199.9257 -67198.0807 87196.1945 127194.2603 207192.2989 07190.2937 267180.2427 -37186.1544 1

7240.5870 -77240.3326 -37240.0381 67239.6985 -287239.3227 -167238.9071 57238.4487 77237.9509 237237.4113 307236.0265 -67236.2060 107235.5451 327234.6346 -337234.0944 157233.3106 397232.4794 -17231.6088 -247230.7024 67229.7490 -237228.7590 -57227.7264 -17226.6501 -217225.5438 727224.3793 -47223.1775 -397221.9390 -267220.6616 117219.3383 47217.9720 -177216.5670 -117215.1207 17213.6348 327212.1008 -37210.5279 -77208.9147 17207.2625 397205.5625 177203.8241 307202.0452 57

estimate for vibrational assignm ent of the band w as again O-O. Molecular constantsand the line position s of this transition are reported in Tables I and III, respectively.The system centered at 7834 cm-, the weakest of all, was analyzed in a similarmann er. This spectrum, wh ich h as been assigned to the l-x 1 transition of PtO, showedfour weak branches, two P branches and two R branches with two R head s at 7870.47 1and 7870.884 cm- (see Fig. 6). The presen ce of Q-dou bling of the rotation al levels


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EMISSION SPECTRUM OF PtO

_~~_ ~7 9 8 0 7 9 7 0 7 s m 7 s s o &J o 0 8 0 1 0

FIG. 4. The A%-X3Z- transition of PtO. The 2-x 1 system is shown here.

2 8 2 3

I7 9 9 0 7 9 9 5

FIG. 5 A. portion of the O-O band of the 2-x 1system of PtO.

..7 8 1 0 P-7 8 2 0 7 . 3 3 0 7 8 4 0 7 8 6 0 7 8 6 0 7 8 7 0FIG. 6. TheA311-X3Z- transition of PtO. The l-xl system is shown here.


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572 FRUM, ENGLEMAN, AND BERNATHTABLE III

Line Positions of the O-O Band of the 2-x 1 Electronic Transition of PtO

J Q,,(J) 0-c Q&J) O-C P.,(J) o-c P&J) o-c

11 7997.938812 7997.651413 7997.360114 7997.040815 7996.698316 7396.341517 7995.954918 7995.543619 7995.105520 7934.646221 7994.170222 7993.689323 7993.150724 7992.604725 7992.034126 7931.441927 7990.826128 7990.187029 7989.522330 7988.837531 798a.L27532 7967.395333 7986.638634 7985.859435 7985.056936 7984.231637 7983.379838 7982.507639 79a1.611240 7980.690341 7979.747442 7978.762243 7977.793744 7976.766245 7975.733046 7974.667847 7973.5837*a 7972.47094% 7971.333s50 7970.169451 7966.963952 7967.776053 7966.551054 7965.296555 7964.013356 7962.697957 7961.3762585960

a2-67-28-40-561312-7

-65-106

-4119-26-14-17-617

-130

-6-2-a-6-29

-102109

25-144

93-1483677716628a439

12716716586

195

7997.aL307997.54657997.25257996.94177996.61597996.25487995.88137995.4aa37995.07367894.64627994.L7827993.68937393.20087992.68167992.13687991.57687990.99237990.39017989.76177sas.lL567866.44767987.75607987.04457986.31237985.55927984.78307963.98617983.16707982.32a67981.46617980.56197979.67567978.76227977.79377976.82547375.63767974.81077373.70357972.72577971.63957070.53757969.41647868.25797367.09067965.90607964.68667963.45367962.18317960.9173

231-7-457

-27-26-11-4a5

-21-127-1%-7

-215

-233

-20-9-3

-1%-22-18-a

-15-13-la

0-6

-13-23115

-54-1

-34-26-14-63-4720

-103-6924

-2132

-62118

7989.8478 27988.8375 -327987.8225 1147986.7604 167985.6907 687984.5782 -aL7983.4640 -1%7982.3286 577981.1632 617979.9735 497978.7622 507977.5206 -257376.2721 5%7974.9857 -77973.6908 697972.3614 307971.0093 -77969.6423 35796a.2579 1337966.8285 111965.3912 417963.92a3 437962.4384 77960.9173 -1107959.3958 07957.8495 957956.2580 -327954.6601 107953.0277 -597951.3007 -427949.7223 957948.0212 397946.3227 2447944.5583 257942.7977 a07941.0015 13793s.la65 -57937.3388 -1127935.5125 2327933.5362 -867931.7001 367929.7974 3317927.8204 1237925.a361 a27923.8555 31%

7989.9926 1427988.9964 LO7987.999L 767986.9665 -679a5.9262 437984.8462 -997983.7709 147982.6600 -227981.5402 6179ao.3650 -37979.2204 487976.0258 67976.8253 1147975.5830 97974.3326 357973.os75 227971.7645 397970.4445 -67969.1070 -157967.7760 2507966.3724 -17964.9748 La7963.5567 447962.1075 -317960.6523 457950.1621 -la7957.6579 -a7956.1369 467954.5906 597953.0277 120794s.aL24 -13794a.Le27 1217946.5442 1827944.8607 1087943.1754 2327941.4327 -27939.7101 La27937.9318 257936.1436 -137934.3435 487932.5117 127930.6478 -1277920.6035 1507926.9160 235

in both states is responsible for the doubling in the R an d P branches. Althou gh a Qbran ch is allowed b y the electric d ipole selection rules, its inten sity is very small andis only rarely observed . The inten sity of the P bran ches was only slightly larger thanthe intensity of R branches. In fact, the R branches were so weak that only a few linesnear the R heads could be measured from the spectrum. Analysis proceeded as beforeand on the b asis of the values of the lower state molecular constants we assigned th isban d as a O-O vibrational ban d again. The molecular constants of this band are shownin Table I. The line positions and the differences between observed and calculatedline positions are given in Tab le IV. Th e fit of this ban d is not as good as the fits ofthe other tw o ban ds because of the poor sign al-to-noise ratio.


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EMISSION SPECTRUM OF PtO

TABLE III-Continued573

J RJJ ) O-C R_(J) o-c

4 8002.8902 -575 aoo3.5379 10668 8005.3093 1259 8005.8299 -150

1011 8006.8832 4312 8007.3656 1013 8007.8368 7414 8008.2805 7515 6008.6955 -616 8008.0803 -17717 8009.4856 6718 8009.8378 -10019 8010.1756 -1920 8010.5067 1142122 8011.0788 114232425 8011.7652 -1226 8011.9554 -1527 8012.1168 -9028 8012.2663 -7329 8012.3841 -1573031323334 8011.6644 -4735 8011.4607 -5036 8011.2286 8737 8010.9388 -11938 8010.6487 -12439 8010.3383 -9640 8010.0096 -2541 8009.6543 742 8009.2706 -1843 8008.4487 7444 8007.SS26 1345 8007.5155 -3146 8007.0166 -5747 8006.5157 12448 8005.9664 5749 8005.368S -5s50 8004.611S 5851 8004.1882 -4552 8003.5378 -18453 8002.8SOZ -6054 8002.2125 25.5 8001.5017 -2s56 8000.7723 -657 8000.0072 -100

8003.5021 4758004.0999 3798004.6759 3718005.2373 12068005.7560 20

8006.7470 -1018007.2128 2988007.6395 -944

8008.4487 -948008.8350 678009.1767 128009.4856 -1408009.7996 -128010.0804 168010.3382 458010.5645 -98010.7785 45

8011.1232 18

8011.36358011.46078011.53198011.58748010.72748010.50678010.26818010.00s68009.71748009.40668009.08038008.69558007.90668007.46458007.01688006.51578006.00638005.48038004.33388003.72508003.09228002.43838001.74928001.042S8000.30247998.5460

-122-70-4460

-34-76-57

5-27-3

111-117-2s-9236

-123-86-25-39-24

474

1::68135

DISCUSSION

From the a2a47r2 electronic configuration of PtO three states are possible, namely,2+, 3Z-, and A. The 3Z- is th e ground state according to Hunds rules. We havenot been able to locate any published ab initio calculations on PtO. However, NiO,although poorly characterized experimentally due to its highly perturbed spectra (8-IO), has been the subject of several calculations (II, 12). In NiO the ground state iscalculated ( 11, 12) and observed to bc X Z ( 10). Both of the ab initio calculations(11, 12) on NiO predict low-lying 311 states.


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574 FRUM, ENGLEMAN, AND BERNATHTABLE IV

Line Positions of the O-O Band of the l-x 1 Electronic Transition of PtOJ P,,(J) o-c Prf(J) o-c R,,(J) o-c Rff(J) o-c

a 7854.95559 7853.9415

10 7852.888711 7851.800312 7850.698813 7849.545214 7848.379215 7847.l7ol16 7845.939617 7844.67441819 7842.038020 7840.674021 7839.293222 7837.860323 7836.400724 7834.917125 7033.395426 7831.840227 7830.269828 7828.657329 7827.019130 7825.347231 7823.648032 7821.916833 7820.154434 7818.368535 7816.545536 7814.694937 7812.815538 7810.904339 7808.968740 7807.001841 7804.990142 7802.975443 7800.924544 7798.832545 7796.728946 7794.590547 i792.42634849505152

1512151a3

-2359

-639

-332655

-5-2310523

-16

-1:-10-2

-29-7

-190

-1-123919la246

3644

-108-228

-6925

29

7852.96777851.91327850.80627849.68627848.51897847.36457846.15197844.91367843.63767842.33l57840.99627839.64027838.24677836.82507835.37367833.89287832.38217830.84357829.27577827.67957826.05287824.39767822.71657821.00367819.26417817.49517815.69947813.87717812.02267610.14107808.23217606.29147804.33747802.33337800.32ol7798.28157796.20417794.10437791.96747789.82217787.64587705.44757783.2122

-261

-96-82

-23837326931

-10-4414-7

-13-20-27-39-37-36-28-35-37-12-19-6-51345363437-399-2826944436

-151

56-1

7870.8724 1937870.7965 547870.7059 627870.5871 a37870.4496 2097870.2728 2337870.0556 1457669.6131 947669.5654 2607869.2562 1587666.9203 177868.5742 78786a.l9ol 447867.7712 -567867.3405 a

7866.3835 197065.8658 507865.3184 607864.7517 1517664.1369 347863.5064 327862.8502 427862.1543 -767861.4371 -140

7870.27287870.15077869.98067869.81317669.56547869.31987669.03647868.71067866.38597666.00397667.60107867.15297666.70607666.21707665.69317865.13747864.54717863.94177863.30537662.61367861.92077861.20157660.4367

-87-5

-87

-88-12-9

-4766

-13-2

-146195740-4

-101-63-46

-295-276-235-350

Since PtO is clearly a Hunds case (c) molecule we approached the problem ofanalyzing the spectrum by treating each component of the triplet state as independentstates. The 0+-x1 transition was treated as a ICY-II transition, the l-xl as a II-II transition, and the 2-x 1 transition as a A- II transition. The following termvalues expressions were used:

F(J) = BJ(J+ 1) - D[J(J+ 1)12 for Z+ statesF(J) = B,J(J+ 1) - D,[J(J+ 1)12 + qJ(J+ 1)/2

+ dJ(J + 1 I 2 0 for II statesF(J) = B,J(J+ 1) - D,[J(J+ 1)12 f qD[J(J+ 1)12/2 for A states,


10/10

EMISSION SPECTRUM OF PtO 575where the upper (lower) sign refers to e (f) parity. The Q-doubling appears as A-doubling in this treatment and therefore we preserve the notation for the coefficients4 and qD*If the 2, 1, and O+ states were to arise from an isolated 311 state then the 1 statewould be midway between the O+ and 2 states and the rotational constant would beequal to the average of the Bs for the 2 and O+ states. Unfortunately, this was not thecase. The 1 state lies at higher energy than expected and the B value is different fromthe predicted value (Table I). This clearly indicates that the 1 state of PtO is stronglyperturbed by other electronic states of appropriate symmetry and confirms the Hundscase (c) character of the A311 state of PtO.

ACKNOWLEDGMENTSThe National Solar Observatory is operated by the Association of Universities for Research in Astronomy,Inc.. under contract with the National Science Foundation. We thank J. W. Brault and G. Ladd for their

assistance in recording the spectra. Acknowledgment is made to the donors ofthe Petroleum Research Fund.administered by the American Chemical Society, for support of this work.

RECEIVED: July 23, 1991REFERENCES

I C. NILSON, . SCULLMAN, ANDN.MEHENDALE. J. Mol. Spectrosc. 35,177-189(1970).2 R. SCULLMAN,U.SASSENBERG,ANDC.NILSSON,C~K. Phys. 53,1991-199911975).3 U. SASSENBERG ND R. SCULLMAN, . Mol. Spectrosc. 68,331-332 ( 1977).4 U. SASSENBERG ND R. SCULLMAN, hys. Ser. 28, 139-l 59 ( 1983).5 K. JANSSON ND R. SWLLMAN, J. ol. Spectrosc. 61,299-3 12 ( 1976).6 G. HERZBERG, Spectra of Diatomic Molecules, 2nd ed., Van Nostrand-Reinhold, New York, 1950.7 B. A. PALMER AND R. ENGLEMAN, R., Atlas of the Thorium Spectrum, Los Alamos National

Laboratory, unpublished, 1983.8. B. ROSEN,Nature 1 5 6 , 570 (1945).9 M. J. MCQUAID, K. MORRIS,ANDJ. L. GOLE, J. Am. Chem. Sot. 1 1 0 , 5280-5285 (1988).

10. V. I. SRDANOVAND D. 0. HARRIS,J. Chem. Phys. 89,2748-2753 ( 1988).I I. S. P. WALCHAND W. A. GODDARD,J. Am. Chem. Sot. 1 0 0 , 1338-l 348 ( 1978 ).12. C. W. BAUSCHLICHER,R., C. J. NELIN, AND P. A. BAGUS,J. Chem. Phys. 82, 3265-3276 ( 1985).

c.i. frum et al- fourier transform emission spectroscopy of the a'^3-pi-x^3-sigma^- transition of...

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