A . K . Ghaudhry and K. N , Upadhya

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O N T H E ^ n - i S + T R A N S m O N O F A l C l M O L E C U L E A. K. CHAUDHRY a n d K. N. UPADHYA

Department of Spectroscopy

Banabas ITinou University

Varanasi-5 {Eeceived July 20, 19G8)

( Plato 14)

ABSTRACT.

The bands of ( A—X) system (2r)00-3000A) have been studied under mi(!rowave dis( hargo by photographing those on lO.G metro grating spectrograph in the third order (dispersion .22 A/mm.). The rotational stnu-ture of (T), 4), (o. .5), (0, 6), (G, 7), ^7.

(7, 10), (8, 10), (8, 11) and (9, 11) ban<ls have been analysed. The rotational (‘onstants hav(' boon reported. Attempts have boon ma b^ to explain reversal of shodincr in the baud syst'^m.

I N T R O D U C T I O N

The A -X sy«teni of AlCl molociile lying in tho n^giou (2r)00-2800A) have heeii

«tudied in low resolution by Bhadiiri and Fowler (1934) and Mahanti( 1934). Holst (1935) performed rotational analysis of six bands (b, 11), (9, 12), (9, 13), (10, 14), (10, 15) and (10, 16) and reported rotational constants for these vibrational levels.

Tlae instrument used for this work was a 6.5 motor grating spoetrograph, tho reso

lution was probably insuffieiont to resolve the })ands having lower vibrational levels in both the A —X states. The systtmi lias red as well as violet shaded bands. Tlio reversal of shading in tlie sequoners has not been explained by pro vious workers. In the present paper rotatioucal analysis for (5, 4), (5, 5), (6, 6), (6, 7), (7, 9) (7, 10) (8, 10), (8, 11) and (9, 11) hands are reported. Tlio rotational constants for those vibrational levels have boon us<?d to explain tho reversal ol shading in Av ~1 and Ar ™ ~ 2 soquoneos.

E X P E R I M E N T A L

Tho bands are ox(*ited eonvouiently under microwave disehargo using Raytheon Mierowthorm oscillator with 2450 Me/soc froqueno,y. Pure sample of AICI3 which is dehydrated well have boon used in tho experiment. Bands w^ere photographed on the Hilgor Large Quartz spectrograph and on tho 10.6 metre grating spectro

graph in the third order with dispersion of 0.23 A/mm. The intense bands could be photographed in sovon hours and woakor in ten hours. A corning glass 7-57 filter was used for cutting off radiation from socond order. A low current iron arc was used for comparison. The rotational linos were measured correct up to 0.05 cm-^

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On the ^^—^^+Transition of AlCl Molecule

545

R O T A T I O N A L A N A L Y S I S

Nino red degraded bands (5, 4), (5, 5), (G, 6), (6, 7) (7, 9), (7, 10) (8, 10), (8, 11) and (9, 11) wore found suitable for the inoasiiremont and analysed. The overlapping structure of the accompanying bands could be minimised to consider- able extent by adjusting the time of exposure. Tiiv, two heads for each bands are E and Q whicli are iiicidy observed on th(^ plates. In tlu* typo transition

iho structure should show P, Q and R bran^dies. Figure 1 (plate 14) shows the siKM'ti’ogram of band (8, 10) which show's the lines due to Q and P l)ranches. In tlio jwesont case the R branch after forming bead dies out very rapidly, honc^e only Q and P branches arc obs<'rved for large J values. The following (lombi- iiation diff(Tences were made.

AiPV) - Q(J+})~P{J+\)

\ F V ) - Q{J)-P{J+\)

The bands of common level w^oro selected and the combination diffor(mcos wiu*(‘ compared. The analysis and ab.soluto J numbering wn)n3 done in the usual maniKT (see Horzberg, 19b0). The upper and lower state constants wore cal-

A Fi J)

ciliated by making plots of - ’ ^ versus (J-\ 1)‘^ tlu3 intercept of wliich gives J't'l

The band origins wc^ro obtained from the graph Q{ J) versus J (i/f J).

The values wore also diocked from the slope of this graph. Tlic (9, 11) band was analysed by comparing combination differences with (8, 11) l)find. The J numbering for this band has (liangtul from those reported by Holst<

(I9J15). The interaction constant a w'as calculated theoretically from Pekoris relation

w, w,

Tliis relation gives ~ .0024 enr^ which is in good agreement with the ob- f-erved values 0.0027 cm^h The wavenumber assignments to different J value's ar(3 given in the table 1.

R E V E R S A L O F S H A D I N G

The shading of a band depends upon the values of the upper and lower vibrational levels. If the equilibrium rotational constants B', and P% of the system differ only by a small amount, the difference which depend on

may change its sign at some higher vibrational levels with the result that the shading of the band also changes. In the band system under investigation

1 and Av = sequences show* reversal of shading. The versus

111

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5 4 6

A . K . Ghaudhry and K. N , Upadhya

Table 1. Wave numbers o f P and Q linos of (9, 11), (8, 11) and (8, 10) bandn o f A i d m o le cu le \ { A - X ) Hystcm)J

. 1 1) (f. 1 1) )8.^{1 0})

J QM) p ( j) 0(1) p ( j) ₀(1) (Pel)

20 36663.95 t>l 63.08

2 2 62.33 36348.46

23 (U.30 47.51

24 fiO.58 46.66

25 59,78 30647.30 45 80 36333,68

20 58.79 46.15 44.92 32.65

27 57.73 45.01 44.18 31 .50

28 56.67 43.87 13.35 30.35 36782.72

29 55.60 42.51 42 52 29.25 82.00

30 54.55 41 18 41.63 28.05 81 .0 1

31 52.51 39.93 40.79 27.00 80 19 36766.93

32 52.42 38.62 40.00 25.81 79.49 65.73

33 51,28 27.18 30.17 24 71 78.63 64.40

34 49.93 35.69 38.24 23.46 77.67 63.04

35 48.67 34.10 37.37 22.25 76.69 61.63

36 47.37 32.45 36.60 20.97 75.76 60.31

37 46.06 30.80 35.46 19.55 74.75 58.93

38 44.71 29.15 34.39 18.10 73.77 57.48

39 43.24 27.41 33.38 16.80 72.65 56.04

40 41.88 25.56 32.35 15.36 71.53 54.48

41 40.55 23.70 31.30 13.90 70.45 53.01

42 39.24 21.77 30.15 12.40 69.24 51.48

43 37.73 19.93 28 91 10.90 09.09 50.02

44 36.18 18.15 27.75 09.35 60.93 48.38

45 34 56 16.09 26.50 07.72 65.73 46.70

46 32,98 14.00 25.36 06.06 64.40 45.07

47 31.27 11.95 24.11 04.40 63.04 43.34

48 29.51 09.93 22.73 02-75 61.63 41.55

49 27,66 07,75 21.42 0 1 . 0 2 60,31 39,81

50 25.89 05.65 20.08 36299.38 58.93 38.08

51 24.21 03.54 18.71 97.65 67.48 36.28

62 22.23 01.30 17.25 95.60 66.04 24.35

53 20.13 36599.00 15.78 93.81 64.48 32.30

54 18.15 96.60 14.21 91.70 53.01 30.30

56 16.09 94.00 12.71 89.70 51.48 28.25

56 14,00 11.13 49.81 26.20

67 11.95 09.35 48.27 24.20

58 09.93 07.72 46.54 2 2 . 1 0

69 07.75 06.06 44.71 2 0 .1 0

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Table 1 (contd.) Wave iinnibeTP of P and Q hranehos of (7. 10 and (7, b) l)aii(ls of AlCl rnoleeulo (A-^X system)

On the ^U-^^+Transition of A id Molecule

547

10) (7, 9)

J Q(J) P(.J) OeO .1’ T)

29 30446.80

30 46.05

31 45.43 30888.54

32 44.88 87.99

33 44.25 87.35 30873.07

34 43.72 80.75 71.90

35 42 03 36427.53 8 6 .1 0 71 04

30 42.29 26.53 85..50 09.92

37 41.72 25.68 84.81 09.81

38 40.93 24.53 84.09 07.59

39. 40.25 23.35 83.34 06.37

40 39.47 22.15 S2.59 05 18

41 38.68 2 1 .0 0 81.81 04.08

42 37.90 19.77 80.99 62.95

43 37.11 18.59 80.13 01.73

44 36.29 17.45 79.35 60.44

45 .35.39 16.19 78.40 59.10

46 34.44 15 00 77.54 57.87

47 33.65 13.71 70.03 56.62

48 32.69 12.31 75.72 55.27

49 31.64 10.84 74.70 53.62

50 30.77 09.30 73.80 52.22

51 29.84 07.90 72.74 50.80

52 28.68 06.30 71.68 49.34

53 27.53 05.83 70.62 47.90

54 26.52 03.37 69.52 40.45

55 25.38 ^{0 1 .8 8} 08.44 45.00

56 24.27 00.47 67.23 43.43

57 23.23 36399.00 00 .0 0 41.90

58 22.06 97.46 04.87 40.38

59 ^{2 0 .8 6} 95.96 63.64 38.83

60 19.64 62.41 37.19

61 18.40 61.09 36.42

62 17.15 59.81 33.56

63 15.87 58.47 31.05

64 14.49 57.08 29.50

65 13.07 55.67 27.47

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5 4 8

A . K . Chaudhry and K . N . Upadhya

Table 1 (ccntd.) Wave numbers o f P and Q branches o f (0, 6) and (6, 7) bands o f AlCl molecule {A —X system)

(6. 6) (6, 7)

J QvJ) p ( j ) QvJ) p ( j )

24 37882.07

25 81.54

26 81.00 37868.78

27 80.40 67.72

28 79.86 66.73

29 79.35 66.87

30 78.70 64.81 37426.30

31 77.97 63.65 26.70 37411.13

32 77.26 62.60 25.10 10.13

33 76.45 61.47 24.45 09.07

34 75.70 60.32 23.75 08.12

35 74.97 59.12 23.15 07,02

36 74.11 57.97 22.25 0.601

37 73.28 56.87 21.55 05.06

38 72.51 55.60 20.80 03.99

39 71.68 54.48 20.04 0 2 .8 6

40 70.82 53.27 19.27 01.73

41 69.86 52.18 18.55 00..54

42 69.06 50.82 17.73 37399.50

43 68.19 49.50 16.30 98.17

44 67.22 48.15 16.02 96.98

45 66.24 46.72 15.19 95,70

46 65.29 45.39 14.37 94.45

47 64.27 43.90 13.45 93.05

48 63.36 42.61 12.56 91.65

49 62.26 41 05 31.54 90.41

50 61.21 39.53 10.73 88.05

51 60.14 38.10 09.80 87.46

52 59.00 36.62 08.86 86.05

53 67.81 35.03 07.82 ^—

54 ^____ 33.57 06.72 83.24

55 55.59 31.97 05.70 82.00

66 54.42 04.52

57 62.97 03.45

58 51.69 02.40

69 50.36 0 1 . 1 1

60 48.97 37399.85

61 47.59 0 8 .8 0

62 46.22 97,68

63 44.87 96.21

64 43.25

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On the Transition o f A lC l Molecule

_{5 4 9} Table 1 (contd.) W ave numbora of P and Q branches o f (5, 0) and (5, 4)

bands of AlCl molecule {A—X.) system)

(6,5) (5. 4)

J Q(J) p ( j) CKJ) P(J)

26 37964.35

26 63.82

27 63.32 38424.26

28 62.82 28.58

29 62.29 28.87

30 61.76 . 22.38

31 61.15 21.74

32 60.62 ^____

33 69.97 20.54

34 59.37 37944.78 19.70

35 58.78 43.72 18.97

36 59.18 42.77 18.24

37 57.49 41.50 17.48 38400.94

38 56.80 40.41 16.70 38388.89

39 56.07 39.07 15.98 98.56

40 55.33 37.84 15.15 97.33

41 54.64 36.65 14.35 96.19

42 53.83 35.50 13.45 94.93

43 53.14 34.36 12.61 93.87

44 52.39 33.18 11.71 92.55

45 51.58 31.94 10.78 91.22

46 60.73 30.66 09.71 89.89

47 50.00 29.27 08.89 88.54

48 49.09 27.96 07.95 87.20

49 48.21 26.63 06.99 85.88

60 47.33 25.32 05.91 84.40

61 46.40 24.07 04.98 82.95

52 45.43 22.84 03.80 81.48

53 44.60 21.48 02.83 79.87

54 43.47 20.17 01.63 ^—

55 42.48 18.84 00.56 76.69

56 41.60 17.43 38399.41 75.00

57 40.42 15.99 98.15 73.63

58 39.36 14.51 96.97 71.82

50 38.29 12.99 94.67 70.19

60 37.18 11.42 94.49 68.59

61 36.04 09.64 93.23 66.91

62 34.94 07.98

63 33.77 06.33

64 32.69

65 31.37

66 30.16

67 28.84

68 27.49

69 26.17

70 24.70

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6 5 0

A . K . Ghavdhry and K . N . Upadhya

V graph for Av = — 1 and Av = —2 soquoncos are drawn in figure 3. It shows clearly that the bands (2, 3), (3, 5) should be headless which is also observed in epoctrum as shown in figure 2 (plate 14). The bands after the point of irit(3r8oction show rod shading and those before the intersection show violet shading. The rod and violet degraded bands are marked in figure 2 (plate 14)

22

20

Bv

0 6 13

Figure 3 : Variation of Bv and with v in tho sequences — — 1 and AP ■■ —2

Table 2. Rotational constants o f (i4^II“ *^SX) system of AlCl molecule Band

atffiignmont

^V', V ’ )

B,/ cm~i) Vo (cm-»/

5, 4 0.2220 0.2320 38431.70

5, 5 0.2220 0.2310 37970.00

6, 6 0.2202 0.2302 37888.50

6, 7 0.2202 0.2297 37436.00

7, 9 0.2176 0.2280 36898.50

7, 10 0.2176 0.2275 36.466.20

S, 10 0.2136 0.2276 36793.80

S, 11 0.2186 0.2270 36354.60

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CHAUDHURY ^AND ^{K. N.} UPADHYA. Indian Journal of Physics Vol. 42, No. 9

PLATE 14 A

Figure 1. Rotational ^structureof (8,10) band of A-X system of Al Cl molecule. ^

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A. K . C H A U D H U R Y ^{a n d} K . N. U Pa d h y a. Indian Journal of Vol. 42, No 9

p l a t e 1,3

Figure 2. Reversal of shading in the band system (A-X) of A l C I molecule.

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On the ^Ti.—^'S.+Tranaititm of A id McAecvle

⁶⁶¹

The A type doubling etmstant for m state could not be calculated due to lack of JS lines. The rotational constants aro summarised in table 2.

AlCl molecule is isoelectronic with CO and SiO. The ground state can be derived in comparison with CO from thci olectron configuration

. . (om)Sx(rY^ . .

Tlie A state may be derived from tlio (jonfiguratioii

. . (0i7r)^{X(T){V7T) . .

A C K N O W J. E D G E TVI E N T

The autiiois arii thankful to Prof. N. L. Singh for his kind interest in the work They are grateful to Drs. 1). K. Rai and K. P. R. Nair for their suggestions and (*o()])erations. One o f us (A. K. Chaudhry) is grateful to C.S.I.R. N(^w Delhi for the financial assistance.

R E F E R E N C E S

Hhaduri, B. N., Fowit^r, A., 1934, P roc. B o y . S oc. L ondon, A145, 321.

Horzberg, O., 1950, Spectra o f diatmnic molecules. I). Von Nostrund Co. Inc. ^C.Y.

Holst, W ., 1935, Z . F u r P h y s ik , 93, 55.

Mahwnti, P. O., 1934, Z . F ur P h ysik , 88, 550.