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JOURNAL OF MO LECULAR SPECTROSCOP Y 153,73-80 ( 1992 )

The Infrared Emission Spectrum of Gaseous AIFHARTMUT G. HEDDERICH AND PETER F. BERNATH .2

Centre for Molecular Beams and Laser Chemistry, Department of Chemistry, University of Waterloo,Waterloo, Ontario, Canada ML 3GI

The high-resolution infrared emission spectrum of aluminum monofluoride has been observedwith a Fourier transform infrared spectrometer. More than 500 rovibrational Iines from bandswith o = 1 + 0 to u = 5 -+ 4 were assigned. The infrared data have been combing with previousmicrowave and millimeter-wave transition frequencies from the literature to yield improved Dun-ham coefficients for the X Z+ ekctronic ground state of AIF. Q 1992 Academic pm, hc .

INTRODUCTIONAt high temperatures aluminum monofluoride is easily produced in the gas phase

by heating A1F3 or a mixture of AlF3 and Al. There is chemical evidence that AlF isthe stable constituent of aluminum-fluorine systems at high temperatures ( I ).AIF has been the subject of numerous spectroscopic studies. The electronic spectraof AIF were recorded both in emission (2-7) as well as in absorption ( 7-13). Anexcellent overview of the electronic spectra was given by Barrow et al. (13). Themicrowave spectrum has been intensively studied ( 14-18). A compilation of the data

can be found in Huber and Her&ergs book ( 2 9).AlF has also been observed to give stimulated infrared emission (laser action) in

an exploding wire experiment (20). Visible chemiluminescence has been observedfrom the reaction of Al vapor with various fluorine containing molecules (21-23).Dyke et al. have reported the photoelectron spectrum (24). Recently, Dearden et al.(2.5) observed Rydberg states of AlF by using resonance-enhanced multiphoton ion-ization (REMPI) spectroscopy. In addition there are several excellent ab initio cal-culations of the molecular properties of the ground and excited states of AIF (26-28).In the infrared region a matrix isolation spectrum (29) and a diode laser spectrum(30) have been studied in detail. In this work we present the Fourier transform emissionspectrum of AIF. The spectrum was accidentally found during an attempt to measurethe infrared spectrum of MgF2.

EXPERIMENTAL DETAILSThe high-resolution infrared emission spectrum of AlF was observed with the

McMath Fourier transform spectrometer of the National Solar Observatory at KittPeak. The unapodized resolution was 0.0055 cm- with liquid helium cooled As:Sidetectors and a KC1 beamsplitter. The spectral bandpass was limited to 500- 1400cm- by an InSb filter for the upper limit and by the detector response and the trans-mission of the KC1 beamsplitter for the lower limit.

Camille and Henry Dreyfus Teacher-~hoIar.2 Also: Department of Chemistry, University of Arizona, Tucson, Arizona 85721.

73 0022-2852/92 $5.00Copyr ight 0 1992 by Academ x Press, Inc.All rights of reprcductm in any form reserved.

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HEDDERICH AND BERNATH

v=l->o , I IR( 1 7 ) R I f t I R ( 1 9 )= 2 - > 1 I I IR 1281 R 291 R 301 R I 3 1

v = 3 - > 2 , I I IR 42) R 1 4 3 ) R ( 4 4 1 R I 4 5 1

L i F L i F/ /

L I F

8 1 0 8 1 1 812

Rl;a, R ( 2 1 )I IR I 3 2 1 RI 3 3 1 R I 3 1

I I I IRI 4 6 1 R I 4 7 1 R I 4 8 1 R ( 4 9L I F

L i F

813 8 1 4Wavenumber (cm-)

FIG. 1.A portion of the high resolution infrared emission spectrum of AIF and LiF (8 IO-8 I5 cm-).

Solid MgF2 was heated to about 1500 K in an alumina tube furnace. The apparatusused was described in detail in the observation of the SiS emission spectrum (31).Deposition of solid material onto the KBr windows was avoided by pressurizing thesystem with 5 Torr of argon. The temperature of the furnace, as measured by a chromel-alumel thermocouple placed between the heating elements and the ceramic tube, wasincreased at a steady rate of about 5 Kjmin. A series of spectra were taken as thefurnace heated up and then cooled down. Initially a globar was placed behind thetube furnace and its image was focused on the g-mm aperture of the Fourier transformspectrometer. No absorption spectra were observed, but when the globar was shut off(at a temperature of about 1300 K) a strong emission feature was monitored. Athigher temperatures the line intensities increased. The maximum temperature whichis accessible with our current oven system is about 1500 K and it was at this temperaturethat the best emission spectrum was obtained. The emission signal decreased rapidlyas the furnace cooled and disappeared at about 1200 K.

RESULTSThe emission features were observed in the region where the infrared spectrum of

MgF2 was expected. However, the high-resolution spectrum showed a pattern typicalof a diatomic molecule. After some thought and a literature search, we found that theemission spectrum belonged to LiF (32). At higher temperatures MgF2 could reactwith water, which is always present in our system, and form HF. Pure rotational linesof HF were observed in the spectrum (33, 34). The HF reacted with Li impuritiesand formed LiF (33). After assigning the LiF spectrum, several hundred emissionlines with weaker intensities remained (Fig. 1). A literature search showed that theselines belong to AlF (30). The explanation for this observation is, presumably, thereaction of HF with the alumina tube at high temperature.

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INFRARED EMISSION OF AlF 75TABLE I

Observ ed Line Positions of AIF

7.5 7673 i472 i371 ;??O iibX hY67 686.5 6b64 b.563 6462 6361 6259 6038 5957 5x56 ii55 -5664 5553 i452 5351 j250 3149 io4x 4Y47 1846 4i45 4643 .lJ42 4341 $240 4139 4038 393; 3836 3335 :ifj34 3533 3432 3331 3230 3129 3028 2926 725 L%4 252 2320 2119 2018 1917 1816 Ii1.5 1614 1513 1412 1311 12IO 11

9 10a 9i 5* i3 4I 22 13 24 :16 ii 68 i9 8

10 911 1013 12L4 1315 I4

ohwrvd ohs.-talc. u n c e r t a i n t y 1 f ' , I l f l ohserved ohs:caic. uncertainty/cm- /lOscmF /lO%d16 ii I 0 808.92433 -8 i0

6 7 9 . 2 2 5 9 6682.78345686.31002

807.98443

688.06226689.86437691.54065694 9a805696.6Ya45700.08838701.78458703.46277705.13485706.79775710.09783ii i 73608713.36489714.98618716.59894718.20357719.79962i2138672722.96571724.53589i26.09784i27.65116729.Mo9730.73200732.25917735.28783736.78884i38.28170739.76560741.24232742.70607i44.16322745.61144747.05044748.480%749.902267Al.31430752.717747.54.11184755.49681756.87290759.59695760.94616762.28481764.93689767.54652768.84123770.12428771.39831772.66288733.91731775.36323716.39882777.62537778.84203780.04886781.24686782.43485783.61295787.08965i88.22892no.47809794.85781795.92846796.98884799.07704800.10952801.12946802 13956803.13938804.129o58tNliiR807.03715

36

-138

21194

-443163

-4673

-26-111

1238

-538

-31-16-15

1429-5

1-22-13

-916

1-17-15-36

531

22 1-1

6II-131213

-912

7-214

-1961

916 3

-2063

-164

22-2726-10

8-6

-43-2

3-14

4-1

-4;1

16-208

24102117I?

-922

5 05 05050

10 0.jOi0

10 0.jO

10 050

1.50.jO50.505050io50.5050405050505050505050505050

25 05050505050SO5050.505050.j@

1M )$0

20 020 0

505050505050505050SO505050M50.xI50SOSO

20 05030.xl.jO.%.5O50

15 0

17 1618 Ii19 1820 IY21 2022 2123 2?24 2325 2426 2.527 26?a 729 2830 2931 3032 ai33 z34 a335 3436 3937 1638 Ri39 3840 $941 4042 1143 4244 4345 4446 4.j47 4648 4749 4850 19Sl .Xl52 ZY53 .5254 5355 5456 55.57 5658 ii59 j860 i961 6062 6163 6264 6365 6466 656i 6668 6769 6871 7074 i375 7476 i377 i678 ii79 ita80 i9a1 8083 8287 8688 87a9 8890 8991 9076 ii74 7573 7472 73i0 il69 i067 6866 6765 66 2 I

X09.8.527.5810.77071XI 1.67640812.5157.5813.461768143389.3815.20506816.06076816.90581817.i1025M18.56431819.37905820.18051820.97300821.7.5436822.52545823.28725824.03544824.77426825.50247826:2195Y826.92619827.62204828.30644828.98a91829.64395830.29634830.93756831.56781832.18705x32.795.53833.39272833.97872834.55407835.11818835.67093836.21271836.744328837.26243837.77058838.2680(1838.75368839.22807839.69117840.14289840.58354841.012lY841.42996841.83637842.23102842.61446842.98617843.34669844.63287844.97470845.26516845.54396845.81285846.06778846.31167846.54466846.76431847.t7019847.83937847.97724848.10364848.21811848.31932672.45038675.96306677.70613679.442256a2.89188684.60413688.00680689.69453691.37525

304

12-i6

-65

18164a

13 6-616

-110

15 094

14-9-3

9-38

80

18149I189

-137

13-4-4-8

-34-39

7420

-616

-25-20

3-12

-2-16

213-26

-61-97

46-37-50

22-63-32-2

3912 922 3IYl23

11 63

-2224

-2481

-29-37

50.5050.50

100io505050i0i0

15 050505050

15 05050i05050505050.5050505050505050SO50.50.5o.5O50505050505050505050505050505050.%

10 010 0

50505050

IO 0.%50,50

15 020 020 0

501.50

50505050

1Cil5050

.f f ii if,i8 79 I 0ii 78

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76 HEDDERICH AND BERNATHTABLE I-Continued

s J if 1 IwrvPII IE~CRI~.~ n r r r t a i n l y . / " , , $ 1 OI W! " m l d , s . GA. l l l l r r r l r l l l l y- -64

63 6462 fi361 6260 6159 6058 .5Y57 58i6 ii5.5 5653 5452 5351 5250 51.49 5048 4Y47 4845 4644 4543 444 4340 4139 4038 3937 3836 3735 3634 3533 3432 3331 3230 3129 3028 2s26 2725 2624 2523 2422 2321 219 2018 1917 1816 li15 1614 1513 1412 1311 1210 11

9 108 97 86 73 42 33 26 37 68 79 8

12 1113 1214 1315 1417 1618 li19 1820 1921 2022 2123 2224 2325 2427 2628 2729 2830 2931 3032 3133 32

694.71342696.36976698.018306YY.6.5ii4iO1.29036iO2.91398i04.52975i06.13673iO7.7355ii10.90866712.48210714.04i62715.60477il7.1.5297718.69321720.2%452723.26203724.76i.59726.26461727.75314730.70357i32.16551733.61902735.06345i36.49933737.92630739.34403740.75277742.15332743.54412744.92638746.29964747 66353750.36431751.70105753.02864754.34697755.65608i56.95600759.52805i60.79984762.06247763.31584764.55975765.i9438767.01948768.23504769.440777i0.63774771.82397773.00242774.17008775.327567i8.74449ii9.86366786.37378789.49700790.51745791.52866792.5288s795.47065796.43114797.38225798.32116800.17100801.07990801.97920802.86794803.74630804.61392805.47231806.31954807.15658808.79909809.60458810.39970811.18411811.95798812.72130813.47359

401933

-4iI2

-i1s

-13-2.5

-1-42-32-13-42-1s-28

8-2-218

7-14

1-11

619

-3-32

14-Ii

-117

337

12968

15-9

-14-8-8

61110

-2319

5 0 35 345 0 36 d.5S O 38 .3 i5 0 39 :38i 0 40 .I93 0 41 4050 22 1150 43 460 44 4:s50 45 4450 46 4.5i0 47 46i0 48 ki50 49 48i0 i0 I950 51 i050 52 5150 53 52SO 54 5350 5s 5450 56 5550 58 5750 59 i850 60 .5950 61 6050 62 6150 63 62SO 64 6350 66 6.5.50 6i 6650 68 6750 69 68SO 70 6950 72 il50 73 7250 74 i350 75 7450 77 i650 79 i 850 82 8150 87 86.50 70 7150 69 i050 68 69SO 6i 6850 66 6750 64 6550 63 6450 62 6350 61 6250 60 6150 59 6050 58 5950 57 5850 56 5i

10 0 55 5650 54 5550 53 5450 52 5350 51 5250 50 5150 49 50

10 0 47 4850 46 4750 45 4650 44 4550 43 4450 42 43SO 41 4250 39 4050 38 3950 37 3850 36 3750 35 3650 34 3550 33 3450 32 3350 31 3250 30 3130 29 30

2 12 12 I2 I2 12 12 12 I2 I2 12 12 12 12 I2 i2 I2 I2 12 I2 I2 12 12 12 12 I2 12 12 12 12 12 I2 12 12 12 12 12 12 12 12 12 12 13 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 23 2

814.21690 75X14.94776 15815.66849 11817.07793 13817.76653 13X1 8 . 4 4 4 i Y 5 7819.11044 -x2819.76737 -10820.41286 2d?l.04748 13821.66970 -128822.28378 9822.88535 -12823.47610 -19X24.05620 7824.62522 24xS.18288 YY25.i2958 2826.26558 328 2 6 . i 8 9 9 7 1 0827.30330 -6827.80566 -5628.77687 -3829.24562 -9829.70345 17830.14943 -17830.58371 -93831.00869 30831.42067 -16832.21145 -20832.58987 -12832.95700 7833.31209 -3s833.65620 -29834.30979 -37834.61865 -108834.91828 52835.20413 -9835.74396 158836.23467 64836.88363 -29837.73384 179674.35579 89676.05402 11 667i.i4320 25679.42516 2681.09914 -27684.42469 64686.07388 -49687.71653 -12

4631

-400

-25-93

27-344-9-113

10 4-834

-1111

i-3

-5312

01110

51571

-1-46

6 8 9 . 3 5 0 6 3 -23690.97715 17692.59578 82694.20516 37695.80650 6697.39945 -42698.98493 -13700.56180 -18702.13048 -13703.69052 -39705.24344 59706.78537 -105708.32135 -22711.36678 25712.87613 -15714.37776 24715.87025 5717.35418 -13718.83004 23720.29672 4723.20460 19724.64604 82726.07705 -23727.50052 -6728.91460 -48730.32057 -19731.71751 -7733.10552 -1734.48458 0735.85486 17737.21579 -6

i 05 0i 05 05 0

1005 0i 0, 5 0

15 05050i0i0SOSO5050505050505050SO

10 0505050,5050505050

10 05050

15 05050

20 010 015 0505050

10 050505050

10 0J O50505050505050

10 0505050505050505050

10 0505050505050505050

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27 28 3 225 2628 29

3 224 2s

3

3 2

2

23 24 3 222 23 3 22 1 22 3 220 El 3 219 20 3 2Id 19 3 2l i 1 8 3 216 17 3 215 16 3 214 1.5 3 213 14 R 212 13 :1 2I1 12 .J 210 11 3 2

9 10 3 28 9 3 17 x 3 25 6 3 23 4 3 23 2 3 25 4 3 27 6 3 2

10 9 3 211 10 3 213 12 3 214 13 3 216 15 3 217 16 3 218 17 3 219 18 3 220 19 3 221 20 3 222 21 3 223 22 3 224 23 3 22.5 24 3 226 25 3 227 26 3 228 27 3 230 29 3 231 30 3 232 31 3 233 32 3 234 33 3 235 34 3 236 35 3 237 36 3 238 37 3 239 38 3 240 39 3 241 40 3 242 41 3 243 42 3 244 43 3 245 44 3 246 45 3 247 46 3 248 47 3 250 49 3 252 51 3 253 52 3 254 53 3 256 55 3 257 56 3 258 57 3 260 59 3 261 60 3 262 61 3 263 62 3 264 63 3 265 64 3 266 65 3 267 66 3 268 67 3 265 66 4 358 59 4 357 58 4 3

739.91264

/

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78 HEDDERICH AND BERNATHTABLE I-Continued

s S !f lf observed ohs.-talc. uncertainty/cm- /10-5cm- /lOWcme49 48 4 3 804.56925.51 50 4 352 51 4 353 52 4 354 53 4 355 54 4 356 55 4 360 59 4 362 61 4 366 65 4 368 6i 4 369 68 4 354 55 5 45152 5450 51 5 449 50 5 446 47 5 445 46 5 442 43 5 441 42 5 44041 5438 39 5 435 36 5 434 35 5 433 34 5 432 33 5 431 32 5 43031 5429 30 5 428 29 5 42728 5 424 25 5 423 24 5 422 23 5 417 18 5 413 14 5 411 12 5 410 11 5 4910 5 4

805.67146806.20624806.72980807.24320807.74505808.23530810.06994810.95076812.53725813.26274813.60946683.36754687.96765689.48564690.99347695.46905696.94490701.32026702.76167704.19339707.03438711.22931712.61214713.96411715.34709716.70303718.04953719.38701720.71452722.03565725.94266727.22482728.50129734.73822739.56521741.92314

-7-7-7

-3711

0-72

287636

-3022

-26-13

9819

-21374638

-86-13

-10451

-10-96

-91213

-9938

16 1-2512 2

-94-50-36-8143.08763

744.24444 40

505050505050

10 050

10 05050505056

10 05050505050

10 050

10 05050

10 0565050

10 050

20 050

15 010 0

5050

10 050

The spectral analysis program PC-DECOMP, developed by J. W. Brault, was usedfor data analysis. The rotational line profiles were fit to Voigt lineshape functions.The strong lines show a ringing caused by the sin x/x lineshape function of the

TABLE IIDunham Coefficients for AIF in cm-

constant this work Ref. (30)Y,, 802 ,323 5 (15) 802 ,324 0 (148)YXl -4 ,849 536 (98) -4 ,849 45 (90)Y30 0 ,019 97 (24) 0.019312(157)

103 Y#J -0.0295(20)YO, 0.552480296(49) 0.552480075(151)

103 Y,l -4.984 214 (60) -4 ,984 385 (248)103 Y*, 0 ,017 53 (22) 0.017274(124)10 F31 0.0503 (24) 0.0331(178)106 Yoz -1 ,048 80 (68) -1.046651(424)109 YIP 1 854 8 (80) 1 ,700 (289)109 Y** 0 ,060 (19) 0.0689(37)102 Yo3 -0.3050(93)

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INFRARED EMISSION OF AIF 79Fourier transform spectrometer. The ringing was eliminated by using the filter fittingroutine available in PC-DECOMP. The signal-to-noise ratio for the strongest linesbelonging to the fundamental band of AlF was about 50 and the resulting resolution-enhanced linewidth was 0.0005 cm-. Pure rotational lines of HF were used for absolutecalibration (1tO.0002 cm- ) of the spectrum (34). For this calibration the HF absorptionlines, taken in a spectrum at lower temperature, were calibrated against CO:! (35).The AlF line positions are listed in Table I.

Bands with v = I --* 0 to v = 5 + 4 of AlF were picked out by using an interactivecolor Loomis-Wood program which runs on a 486/33 MHz microcomputer. Datareduction was made by using the well known Dunham equation (36)

T(v, J) = C Ye [J(J+ I)].LiPure rotational transitions ( 16, 17) were corrected for the effect of hype&e structureand included in the final fit. The Dunham coefficients are shown in Table II.

ACKNOWLEDGMENTSThe National Solar Observatory is operated by the Association of Unive~ities for research in Astronomy,

Inc., under contract with the National Science Foundation. We thank J. W. Brault, R. EngIeman, Jr., C. I.Frum, and J. Wagner for assistance in recording the spectra. This work was supported by the AstronauticsLaboratory, Edwards Air Force Base. CA, and the National Sciences and Engineering Research Council ofCanada (NSERC). Acknowledgment is made to the Petroleum Research Fund. administered by the AmericanChemical Society, for partial support of this work. H.G.H. thanks the Deutsche Forschungsgemeinschaftfor a postdoctoral scholarship.RECEIVED: October 25, 1991

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