New rotational analysis of the A1Π-X1Σ+ transition of AlBr

JOURNAL

OF MOLECULAR

SPECTROSCOPY

145, 12- 17 ( 1991)

New Rotational Analysis of the A’II-X H. BREDOHL, Institute

qf‘ilstrophysics.

I. DUBOIS, E. MAHIEU, University

‘l2+ Transition of AlBr AND

F. MELEN’

qf‘LicYge.B-4200 Ougrbe-Lic?gc Belgium

Twenty-eight bands of the A ‘II-x rZ+ transition have been fully analyzed. The vibrational constants obtained for the A ‘II state do not agree with earlier data. On the other hand the observations suggest that the conclusion about the predissociation ought to be revised. ‘L IWI Academic Press. Inc.

INTRODUCTION

Two electronic transitions are known for AlBr; Crawford and Folliot ( I) observed the UV system in 1933 and Miescher (2) identified the a311,-X ‘S+ system in 1936. The UV system, which forms the subject of the present paper, was identified as the A ‘IL-X iZf transition by Jennergen (3) who analyzed nine bands including u’ = 0. 1, and 2. Later on, Ram et al. (4) analyzed seven bands of the same system with an extension to the v’ = 3 vibrational level. They reported a break-off in the rotational structure at J = 93 and J = 67 for the u’ = 2 and 3, respectively. More recently, Griffith and Mathews (5) observed this system with a higher resolution; they gave more accurate constants and discussed predissociation. The a311 -X ‘Z+ transition has been partly analyzed by Lahshminarayana and Haranath (6) and reanalyzed up to v’ = 2 by Griffith and Mathews (5). The ground ‘Z+ state is the only one to be known with great accuracy since it has been studied up to 2, = 8 by microwave spectroscopy ( 7, 8). In this paper, we gave a new analysis of the A ‘II-X ‘ZZ+ transition. Twenty-eight bands have been fully analyzed for the isotopic species A179Br, against six in the preceding paper (5). EXPERIMENTAL

DETAILS

The emission spectrum of AlBr has been obtained in a Microtron 200 W discharge in flowing Argon in which traces of AlBr3 were introduced from a heated side-tube, in the same way as the one used for AlCl ( 9). The spectrum was recorded between 2700 and 3000 A in the third order of a 2 1-ft Eagle spectrograph equipped with a 1200 lines/mm grating at an inverse dispersion of 0.37 A/mm. Exposure times from l/4 to 1 hr were needed with a slit width of 1.5 pm on II a 0 Kodak plates.

r Present address: Max Plank Institut fiir Physik and Astrophysik. Institut fiir extraterrestrische Physik. D-8046 Garching bei Mtinchen, Federal Republic of Germany. 0022-2852/91 $3.00 Copyright C’ 1991 by Academic Press. Inc. All nghts of reproduction in any form reserved.

12

THE

A ‘II-X’S+

TRANSITION

OF

AlBr

13

The plates have been measured on a Grant photoelectric comparator against Fe and Ne lines provided by a hollow-cathode discharge. The relative accuracy is estimated to be about 0.02 cm-’ for unblended lines. ANALYSIS

All the observed bands are red-degraded and the vibrational analysis is almost obvious for the 79Br and *‘Br isotopes. No band with v’ > 3 is observed, confirming the predissociation of the excited state. Twenty-eight bands have been analyzed for the two isotopic species and no perturbations have been detected. The rotational lines of all the analyzed bands are given in Table 1 (a and b) which may be obtained upon request from the authors.’ The maximum J value observed for all the bands is given in Table I. It must be pointed out that the lines are observed with normal intensity above the break-off mentioned by the preceding authors (4. 5 ). This problem will be discussed later. DETERMINATION

OF THE

MOLECULAR

CONSTANTS

All the bands reported in Table I have been submitted to an individual fitting. The constants obtained are given in Table II (a and b) for the two isotopic species Al “Br and Al *‘Br. In these fittings, due to their high accuracy. the ground state constants have been kept frozen to their microwave values ( 7, 8). A few H distortion constants have been determined; they are also given in Table II. The individual bands have been merged ( IO) to obtained the B and D values given in Table III. It must be pointed out that BRP and BQ as well as DRp and D, values differ by less than a standard deviation on the constants. The X-doubling in the A ‘II state is therefore negligible at the accuracy of our analysis. The merged values have been used to determine the equilibrium constants given in Table IV. The rotational constants are in reasonable agreement with those of Griffith and Mathews (5) but the vibrational constants of the A ‘II state disagree with the values of Ref. (5) (4% for w, and 63% for w,x,). This discrepancy is still to be understood since, on the other hand, the ground state constants agree with the values reported by Huber and Herzberg ( I I ) . PREDISSOCIATION

A breaking off of the branches has been reported by Ram et al. (4) at J’ = 93 for the u = 2 level and at J’ = 67 for the o = 3 level. Griffith and Mathews (5) reported the same conclusions. On our spectra, the branches can be followed to higher J’ values with a normal intensity distribution. For the u = 2 level, the branches are followed up to J 2: 100. Above this point, it is impossible to say anything about an eventual break-off since the structure is entering the head of the next band of the same sequence; the 3-2 band for instance masks the structure of the 2- 1 band above the last observed (J = 97). ’ A few copies of Table 1 are also held on deposit in the Editorial

Office of the Journal.

14

BREDOHL

ET AL.

TABLE II (a) Molecular

Constants

from Individual

'RP

(A1’9Br) (in cm -’ ) -

Analysis DRpx107

BQ

DQx107

llnax

689

0 154511(12)

0 154512(13)

1 893( 18)

I 894(39)

124

161

0 049

35462

297

0 1544944(56)

0.1545137(48)

1.9300(52)

l9580(35)

119

209

0 054

35089.336

0 i545280(70)

0 1545546(52)

19550(59)

1 9900(33)

126

176

0.064

34722

402

0 154511(37)

0 154497(15)

1 874(76)

1869(15)

98

104

0 086

36120

479

0 1519404(63)

0 1519579(48)

2 2600(68)

2 2940(37)

114

I90

0.047

35746

097

0 151987(13)

0 1521232(90)

* 329(27)

I aa3(12)

90

139

0 062

34638

I75

0 151915(16)

0 151868(17)

2 0790(33)

2 052(35)

104

167

0051

34274

228

0 151773(15)

0 151696(16)

2 39804)

2012(15)

100

136

0094

3:9,2

21:

0 151933fI6!

i, ‘52nl9(11)

2 167(16)

2298(11)

106

74

0071

33553

465

i

0 1:?026(iai

2X3(97)

2 328(42)

110

51

0 078

36385

994

11 148789(24)

0 148804c2:i

2 45000

2474(68)

a5

152

0 046

ibOlO

223

0 145969(14)

0 148998(15)

2 779(34)

2 821(36)

97

,a4

0 045

35637

626

0 148775(13i

n 148795(14)

2441(35)

2 471(26)

96

205

0 050

35267

245

0 1489453(83

0 1489449(921

2 asa

2860(10)

101

223

0 083

151%(1?1

1

34402

722

0 149noia(73

0 1489790(81)

2 8070(82)

2 aoao(96)

96

178

0 063

34539

796

0 14878809)

0 148800(19)

2 432(321

2 456(30)

a2

136

0 096

‘4177

305

0 i48965(23)

0 148914(24)

2 674(60)

2.636(62)

93

164

0 058

33818

165

0 14874(11)

0 14903(10)

,51(X)

2 79(24)

92

102

0 115

3 45(50)

77

74

0 120

33461

807

36255

369

3 11 35511 683

0 14905(171

0 14880(14)

4 lS(55)

0 144523(32)

0 144409(36)

2 842(ao)

2 445(99)

64

93

0081

0 145160(34)

0 145100(24)

363(14)

3 555(a3)

55

93

0 046

0 144945(22)

366(16)

3 314(78)

56

110

0 050

3 512(50)

6,

107

0 044 0 063

0 144991(3i

I

I 1)

35144

000

0 145337(2:,!

0 145349(17)

3 37(

2,478:

653

0 144111?,21)

0 145O17(20)

3732(64)

3 395(53)

65

123

34421

233

0 14113’f23,

c

3 620(57)

7 509(3’)

7,

114

0 054

‘4

2"

(I i45n?l(;PI

3 523l7OJ

3 98(23)

65

94

0 08’

t65

0 ‘45218(27)

3 804(49)

3 295(93)

76

93

0 08:

? 965(52)

357(12)

74

a7

0

jt:

337’f 3335,

73t,

,45OhEi( ‘6: c 145 /q4rj, 1 i4:1:;13:,

CI 146171142,

L

2-2,

SD

35837

35882

H x

Nb 1 ine

J

1011

:

1-4,

0.269(X)

No&. Standard

deviations

O.lZl(26) 2-3,

z-o,

0.314(27)

in brackets

0.271(59) 2-4,

0.215(27)

2-1,

IX

-

0.08&?(25) Z-7,0.38(18)

refer to the last digits.

In the case of the o = 3 level. the same blending cannot happen since the v = 4 level is missing. Nevertheless, the v = 3 level is observed up to J = 76 (3-8 band) and not beyond, due to an apparently normal decrease of the intensity. In any case,

THE

.4 ‘II-.Y’T+

TRANSITION

TABLE Molecular

II (b)

from Individual

Analysis ( Al*‘Br)

(in cm-‘)

-

T

I

Constants

15

OF AlBr

BQ

*RP

DRPXIO

7

DQXIO’

35837 819

0 1535477(72)

0 1535620(56)

19170(66)

19380(37)

35463556

0 1535571(71)

0 1535896(55)

19320(63)

19690(35)

35091

0153605(10)

0 1536471(70)

19630(85)

34719023

0153526(10)

0 1535478(93)

19330(78)

36119667

0 1510493(92)

0 1510617(73j

35744938

0151111(36)

0 151047(18)

672

J

:

Nb

3

ine

121

165

13;

182

2.003(38)

13c

202

1.9360(65)

IlC

138

2 2750(91)

22950(56)

18C

112

0056

2 51(10)

2.262(28)

83

116

0078

34634723

0 150604(18)

0 150676(12)

2 158(S)

2.259(10)

109

145

0089

34269069

0 150915(31)

0 150906130)

2110(41)

2 099(31)

79

85

0067

33906352

0 150980(32)

0 150976(29)

2 268(Z)

2 250(21)

105

76

009?

33545994

0 151143(3?)

0151144(31)

2 376(21)

2 360(20)

109

71

0081

76384477

0 148005(10!

0 147995il

2757c121

2 737(14)

87

126

0050

36010?52

0 1479508(59,

0 1474740(63)

2 6790(86)

2 7190(89)

88

161

3040

35638

504

0 14841(12)

0 1484Oll2)

2921(13)

2901(12)

102

203

3054

35269

470

0148198(95)

0148197(94)

2 625(81)

2 621(80)

99

230

3054

34902

305

0 148679(16)

0 148867(20)

2 331(22)

2 374(33)

79

138

1089

34534

656

0147787(12j

0 147851(14)

2516(18)

2.646(22)

a4

163

1072

3417,310

0148588(13)

0 148590(15)

2 673(14)

2 694(18)

93

140

1097

33811 821

0147948(24)

0147928(22)

2 649(28)

2 633(25)

93

99

,110

33452370

0 148158(321

0 148137(25)

2 574(30)

2526(21)

82

1101

36254

153

0 143474(221

0143483(37)

3340(58)

333(12)

67

120

JO85

35882

163

0143540(19,

0 143515(19)

3498(36)

3.329(38)

74

154

1084

35513178

0144155131)

0 144151(24)

3 70(16)

3578(85)

55

91

1049

35146602

0 144166(X)

0144178(18)

369(11)

3.644(49)

53

113

1050

34778776

0144526(26)

0 144687(40)

3081(54)

3 14(12)

70

107

1094

'-6

34416575

0 143562(20)

0 143512(27)

3588(43)

3324(72)

7,

132

1087

J-7

34056492

014365(1i)

0 14376(12)

3 92(56)

521(71)

47

72

1104

Y,-8

33699078

0143436(38)

0 143279(47)

3228(83)

271(11)

71

89

1123

J- 9

33344

0143505(64)

0143585(54)

331113)

353(13)

70

78

) 142

-

-

-

3-f

,

!56

I )

t H x 1Ol1

Nore. Standard

deviations

2-3,

03

0.386(23)

in brackets

refer to the last digits.

it seems that the discussion of Griffith and Mathews (5) in term of Mulliken’s subcases of predissociation (12) must be considered with caution, although the break-off had been confirmed by recent laser spectroscopy measurements of Wolf and Tieman ( 13 ) Nevertheless, the A ‘II state is clearly predissociated since no levels with ~1> 3 have

16

BREDOHL

ET AL.

TABLE III B, and D, Constants

BR.P

(in cm-‘)

BO

DRP x 10’

Do x 10’

1.962(85)

Ala’ Br

Note. Standard

deviations

0.15355(14)

0.15358(10)

1.94(16)

0.15092(16)

0.15100(15)

2.16(22)

2.29( 17)

0.14791(12)

0.14800(14)

2.40(19)

2.60(21)

0.14398(33)

0.14420(38)

4.01(99)

4.49(1.17)

in brackets

refer to the last digits.

ever been observed. By analogy with AK1 (9) the state responsible for this predissociation is likely to be the ‘A state coming from Al( ‘P) + Br( 2P). CONCLUSIONS

More bands have been analyzed for the A ‘II-X ‘2+ transition of AlBr than in the preceding analysis. The rotational constants have been confirmed but the vibrational constants of the A ‘II state are considerably different. On the other hand, the discussion of the predissociation of the A ‘II state by Griffith and Mathews (5) seems to be questionable. TABLE IV Equilibrium

Constants

(in cm -I)

Aim Br vo

35 876.107

35 877.241

BC

0.155521(28)

0.15462(11)

Q.

0.001768(41)

0.00195(20) 0.000283(54)

7.

0.000344( 12)

De x10’

1.767(17

1.78(11)

0, x 10’

0.424(14)

0.352(93)

303.87(80)

301.75(98)

WC w: n we u.2;

Note. Standard

deviations

Al” Br

in brackets

9.99(18)

9.36( 22 )

377.40(26)

377.23(32)

1.333(27)

1.195(34)

refer to the last digits

THE A ‘II-X ‘Z+ TRANSITION

OF AlBr

17

ACKNOWLEDGMENT We are pleased to acknowledge a grant of the Belgian FRFC (Contract 2.4554.75 ). RECEIVED:

June 29. 1990 REFERENCES

I. F. H. CRAWFORD AND F. FOLLIOT, Phys. Rev. 44,953-954 ( 1933). 2. E. MIESCHER, Helv. Phvs. Acta 8, 279-308 ( 1935). 3. C. G. JENNERGEN,Ark. Mat. .4sfern. Fys. A 35, l-29 (1948). 4. R. S.

RAM, K. N. UPADHYA, D. K. RAM, AND

5. W. B. GRI~TH

AND C.

W.

J.

SINGH, Opt.

PuraApl. 6, 38-63 (1973).

MATHEWS, J. Mol. Speclrosc.

104, 347-352 (1984). 6. A. LAKSHIMINURAYANAAND P. B. V. HARANATH, Cur. Sci. 39,228-229 ( 1970). 7 F. C. WYSE AND W. GORDY, J. Chem. Phys. 56,2130-2136 (1972). 8. T. HOEFT. T. TOERRING, AND T. TIEMANN, Z. Naturforsch. .4: Phys. Phys. Chem. Kosmophys. 28, 1066-1068(1973). Y. E. MAHIEU, I. DUBOIS, AND H. BREWHL, J. Mol. Spectrosc. 134, 317-328 ( 1989). 10. D. L. ALBRITTON, A. L. SCHMELTEKOPF,AND R. N. ZARE, .I. Mol. Spectrosc. 67, 132-156 ( 1977’1. 11. K. P. HUBER ANDG. HERZBERG. “Constants of Diatomic Molecules,” Van Nostrand, New York, 1979. 12. R. S. MULLIKEN, J. Chem. Phys. 33,247-252 ( 1960). 13. U. WOLF ANDE. TIEMAN, Chem. Phys. 119,407-418 ( 188).