The electronic spectrum of bismuth monofluoride

JOURNAL

OF

MOLECULAR

SPECTROSCOPY

83, 317-331 (1980)

The Electronic Spectrum of Bismuth Monofluoride An 0+ -+ X,0+ Band System WILLIAM Depurtment

of Chemistry.

at 3838 A

E. JONES AND THOMAS D. MCLEAN Dalhousie

Universit_v.

Emission bands of BiF (in the region of to the B-X,0+ and A,-X,0+ transitions, analyzed under high resolution. These bands system. Extensive rotational and vibrational nature of the perturbing state is discussed.

Halifax.

Notaa Scotia

B3H 4J3. Canada

3800 A), formerly designated as belonging have been photographed and rotationally have been found to belong to an 0+ + X0+ perturbations have been observed and the

INTRODUCTION

This laboratory has long been concerned with the visible and ultraviolet spectra of the group VA monofluorides. The lighter members of these monofluorides can effectively be classified under Hund’s coupling case (b). However, with increasing molecular weight the interaction between L and S tends to become larger than the coupling to the internuclear axis; that is, the heavier members are more accurately defined under Hund’s case (c ). One way in which this coupling transition manifests itself is in the splitting of the 3Z- state into 0+ and 1 components (spin-spin splitting). This has been observed experimentally for the ground state of this series of molecules, the multiplet splitting increasing with the heavier monofluorides. The spin-spin interaction constants (A) for the first four members have been given as follows (Z-5); NF, 1.22 cm-l; PF, 2.96 cm-‘; AsF, 69.66; and SbF, 399.07 cm-‘. Unfortunately, while several transitions involving the ground state of BiF are known, none have been reported for the (a = 1) component. Because of the large magnitude of the expected splitting, little interaction occurs and the 0+ and 1 components in effect become two distinct states. It was the initial object of this work to locate a transition in the near infrared similar to the bO+-X,1 and bO+-X,0+ transitions observed for AsF (4) and SbF (5). The observation of such transitions would allow determination of the separation of the X,0+ and X21 states and thereafter a complete analysis of the BiF system. A thorough investigation of the photographic infrared region proved unsuccessful in locating the expected transition involving theX, 1 state. During the course of the study, however, several interesting bands near 3800 A were photographed. Their structure merited closer examination. Bismuth monofluoride was first observed in emission by Howell (6) and later in absorption by Morgan (7). Howell’s system, the well-known A-X,0+ transition, has been the subject of several subsequent investigations (8-12). The 317

0022-2852/80/1003 17-15$02.00/O Copyright

0 1980 by Academic Press. Inc.

All rights of reproduction

in any form reserved

318

JONES

AND MC LEAN

most recent work (12), a millimeter wave analysis of the X,0+ ground state, provided accurate rotational constants for this state. A series of weak bands in the uv, first reported by Morgan (7), and referred to as the triplet C system, has also been studied by many workers (13 -16). Avasthi (17) reported a transition around 6000 A which he designated as the A '-X22transition, while Murty et al. (18) reported a second system designated as the Al-X,2 system at 6200 A. They assumed that the A' and Al states lie slightly below the A state, but no rotational analysis was performed on either transition and the assignments are in some doubt. In addition to these four band systems, Pate1 and Narayanan (29) reported a series of bands in the region of 3838 A which, from low resolution studies they attributed to two separate transitions. From high resolution photographs, we have now shown that the bands can be assigned to one transition hereafter denoted as BO+-X,0+. The peculiar structure is the result of strong perturbations in the upper state. Extra lines have been observed in the more intense bands enabling the determination of the approximate rotational constants of the perturbing levels. The perturbations made determination of the upper state constants difficult. In order to obtain more meaningful data, a merge program was utilized as opposed to a “band-by-band” fit. The possible identity of the perturbing state is discussed. EXPERIMENTAL

DETAILS

The BiF emission was generated by a conventional microwave discharge apparatus. Helium containing -2% fluorine was passed over a mixture of BiF, and Bi metal. The blue/green discharge was initiated and maintained with a Burdick Model M.W. 200, 2450-MHz microwave unit, operating at about 80 W. Initial photographs were taken at Dalhousie on a 3.5-m RSV Ebert spectrograph, where the most intense bands (O-O, l- 1, and 2-2) were photographed. The stronger bands were later photographed in the 15th order of a 7.3-m Ebert vacuum spectrograph, which gave a linear dispersion of 0.16 &mm, while the weaker bands were photographed in the third order of a 10.7-m Eagle spectrograph with a linear dispersion of 0.48 &mm. The latter two instruments are located at the National Research Council Laboratories in Ottawa. Type 103a-0 and spectrum Analysis No. 1 plates and a slit width of 60 pm were used. An iron-neon hollow cathode source was used for calibration of the spectra. The lines were measured on a semi-automatic comparator at the National Research Council of Canada, Ottawa, and on an Abbe comparator at Dalhousie. The data were treated with a computer program which established the dispersion curve of the particular spectrograph used, and calculated vacuum wavenumbers from the measured positions of the emission lines. The estimated uncertainty for the unblended lines is 50.01 cm-‘. RESULTS

AND DISCUSSION

When observed under low resolution the BO+-X,0+ band system consists of a series of alternating wide and narrow groups of lines, separated by regions of

FIG.

bands.

I. Au = 0 sequence

O-O to 6-6

of the BO+-X,0+

system

between

3750

and 3850

A photographed

im emission.

indicated

are the band

origins

of the

k

g

2

;;I g ti

9

320

JONES AND MC LEAN TABLE I Deslanders Scheme for Bands Observed in the BO+-X,0+ Transition in BiF 2

1 (508.18)

3

5

4

6

[6_l3913.10 25547.94 (613.64) [8] 3821.31 26161.58

(503.46)

[51 3896.30 25658.12 (600.49)

‘“W&; [43 3793.80 26351.32

[tl

3772.72 26498.57 [l] 3763.W 26566.98

t

Wavelength in air, i + Band Origin, cm-l testrmated relative intensities of the bands

few or no lines. Figure 1 shows the Av = 0 sequence between 3750 and 3850 8, and clearly illustrates this structure. In addition to the seven bands shown in Fig. 1 the O-l and l-2 bands were also photographed and analyzed. The previous analysis of this spectrum (19) had attributed the structure to two separate transitions. This is understandable since weak lines in the vicinity of each band origin and the sudden breaking off in the rotational structure gives the impression that two systems are present, one violet degraded and one red degraded. However, under high resolution each “band” was observed to consist of only one series of lines. A vibrational analysis was made, assuming that adjacent violet and red degraded bands were P and R branches, respectively, and that the most intense transition corresponded to the O-O band. Since bismuth and fluorine are isotopically pure, no confirmation of the analysis on the basis of isotopic shift could be made. However, other evidence described later supports our vibrational assignments, especially those of the lower state. The smaller groups of lines were found to be R lines displaced due to strong rotational perturbations. No appreciable degradation of the bands was observed (Fig. 1) indicating similar upper and lower state B values. This is consistent with the vibrational analysis as given in the Deslandres scheme in Table I. The first and second vibrational quanta of the lower state are in good agreement with those reported earlier for the X,0+ ground state (6). As no Q branch was observed, the upper state was also assigned as an 0+ state. The rotational analysis was straightforward in the main portion of each band. However, difficulties in the rotational assignments were experienced in the neighborhood of the perturbations. Considerable hardship was encountered in the analysis of the

BO+-X,0+ TRANSITION

OF BiF

321

displaced R lines and indeed only the O-O, 2-2, and 4-4 bands were analyzed in their entirety. Lower state combination differences were found for each band and were in excellent agreement with those generated from the millimeter wave study of the ground state (12). The correlation strongly supports our vibrational assignments of the lower state. On the completion of the rotational analysis, the vibrational constants were recalculated using the formulas due to Jenkins and McKellar (20). R,.,,.;(J) - R,,,.;(J) = P,,,,y(J) - P,.,,;(J) = G”(v;) - G”(v;) - (B,., - B,)J(J R,.&J

+ l),

(1)

+ 1).

(2)

- 1) - R,.;,..(J - 1) = P,.L,,(J + 1) - P,.,,,.(J + 1) = G’(v;) - G’(u;) - (B,; - B,,)J(J

The results are given with other molecular constants in Table V. The vacuum wavenumbers of the O-O, 0- 1, l-2, l- 1, and 2-2 bands are given in Tables II, III, and IV. A reproduction of the O-O band showing the rotational assignment is given in Fig. 2. Perturbations at J = 48, 78, and 117 gave rise to apparent bandhead formation. Also indicated are the extra lines that have been observed. In order to obtain meaningful molecular constants, especially of the upper state, a merge program based on the direct approach developed by Albritton er al. (22 ) was used to simultaneously fit 5 molecular parameters (Y~,B’,B”,D’,D’) for a given vibrational band. Modifications made it possible to simultaneously determine constants for levels involved in more than one band, as opposed to a band-by-band fit. Such a program has several advantages over the traditional term value and combination difference techniques. Basically the program correlates the parameters for a given level through a variance-covariance matrix, and does not assume that the variances of the constants are equal. The results yield the minimumvariance, linear, unbiased (MVLU) parameters and the corresponding unbiased estimates of the standard deviations. The O-O, 0- 1, l- 1, l-2 and 2-2 bands were used in the fit, using only those lines which did not appear to be seriously perturbed. The results are given in Table V along with the rotational constants for the other bands as determined by combination differences. The agreement of the lower state constants with those from the microwave study (22 ) is excellent. Rotational constants for the upper state, particularly theD values, are not as precisely determined. The principal equilibrium constants for the X,0+ and BO+ states are given in Table VI. Plots of A2F’/4(J + 112) vs (J + l/2)* established that, as expected, the perturbations manifest themselves in the upper state of the transition. Such a plot, shown for the O-O band in Fig. 3, dramatically shows the change in the upper state rotational constant in the vicinity of the perturbation. The interaction of the respective wavefunctions of the perturbed and perturbing states causes Extra lines, due to a “mixing” and gradual exchange of their properties. I Molecular constants for the 3-3 band were determined from combination differences perturbation at low J values, displaced all observed line positions to some degree.

since a

JONES AND MC LEAN

322

TABLE II Vacuum Wavenumbers 2 0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70

R(rT)

-R(J)

26056.577 57.038 57.501 57.963 58.428 58.891 59.358 59.829 60.297 60.768 61.238 61.712 62.188 62.655 63.136 63.607 64.082 64.56 65.039 65.509 65.990 66.462 66.936 67.413 67.886* 68.360 68.825 69.296 69.765 70.229 70.684 71.134 71.581 72.017 72.499 72.806' 73.640 73.992 74.318 74.601 74.843' 75.028' 75.028' 75.028' 74.a43* 74.445 73.883 72.928 71.790 70.331 68.686 66.781 64.684 62.338 59.839

of the O-O Band -P Ln

-P(J)

26055.655 55.182' 54.742

26105.287 03.745 02.144 00.555 98.959 97.356 95.825 94.335 92.944 91.640 90.662 89.740 89.093 88.611 88.555 88.397 88.397 88.555 88.782 89.093 89.435 89.806 90.236 90.662

26091.141 91.640 92.114 92.616 93.125 93.642

94.158 94.671 95.184 95.682

53.834 53.381 52.931 52.485 52.033 51.586 51.141 50.694 50.254 49.809 49.363 48.921 48.478 48.040 47.599 47.162 46.721 46.208* 45.843 45.404 44.964 44.526' 44.082 43.637 43.192 42.748 42.296 41.840 41.378 40.912 40.455' 39.952 39.477' 38.943 38.315 37.880* 37.258* 36.646* 35.968 35.214 34.386 33.393 32.337 31.056* 29.518 27.747* 25.667 24.322 20.743 17.939 14.951 11.822

26072.886* 70.331' 67.886* 65.247 62.757 60.086 57.584 55.182* 52.749 50.446 48.279 46.288* 44.526' 42.961 41.625 40.455' 39.477' 38.652 37.880* 37.258* 36.646* 36.060 35.563 26035.081 34.620 34.186 33.762 33.366 32.958' 32.574 32.194 31.432

BO+-X,0+ TRANSITION

323

OF BiF

TABLE II-Continued R(J)

J 71 72 73 74 75 76 77 78 79 80 81 82 83 a4 85 86

a7

R(J)

26111.216* 09.750 08.280 07.626* 07.162* 06.886' 06.886* 06.886' 06.886' 07.162* 07.626* 08.111 08.661 09.266

88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115

10.547 11.216* 11.912 12.607 13.321 14.054 14.790 15.539 16.301 17.057 17.824 18.599 19.327 20.149 20.922 21.696 22.449 23.213 23.943 24.631 25.251 25.737 25.951 26.142 26.142 25.951 25.599

'indicates

a double

P(J)

P(J)

96.155 96.606 96.984 97.356 97.493' 97.493* 96.819' 95.387 92.816 89.292

31.056" 30.641 30.222' 29.727' 29.278 28.695' 27.936' 26.990' 25.564 23.184 19.784 15.308

26042.503 40.159 38.048 36.269 34.968 33.945 32.958' 32.008 31.214 30.505 30.222* 29.727' 29.410 29.148 28.864 28.695* 28.450 28.267 28.073 27.936' 27.747* 27.644 27.510 27.389 27.274 27.171 27.027 26.990* 26.896 26.801 26.696, 26.610 26.489 26.354 26.166 25.926 25.463 24.908

24.217 23.32: 22.374 or blended

line.

Note: Second column, line 18. should read 64.560: fourth column, line 53. should read 23.332: second column, line 56, should read 59.829.

“mixing” enabled a graphical determination of the B value of the perturbing state at J = 48 in Fig. 3. In general, however, a graphical extrapolation was not always possible. Therefore relationships (3), (4), and (5) as given by Kovacs (21) were used not only to determine the position of maximum perturbation, but more importantly to calculate the rotational constant of a given perturbing level. this

ARP =

[R(J - 2) - R(J - 1) + P(f)

=I (B” - B;)

fdJ)

=

- P(J

+ l)]

45 + 60’ - 2570”

- D;),

[J-YJ + 1) - P(J) + R(J - 1) - R(J - 211= B, _ B,, B 45

(3) (4)

324

JONES AND MC LEAN TABLE III Vacuum Wavenumbers

of the 0- 1 Band

Vacuum Wavenumbers

0 1

25548.864

2

49.325

3

49.792

4

50.281 50.753 51.242 51.742 52.248 52.715 53.226 53.753 54.244 54.735 55.271 55.782 56.314 56.826 57.366 5,.891 58.437 58.964 59.502 60.053 60.595 61.146' 61.686 62.244 62.790" 63.342 63.884 64.458 64.970 65.511 66.012' 66.556 67.063 67.562 68.029 68.460 68.892 69.223 69.525 69.,46* 69.746' 69.746* 68.525 68.892 68.324

5

6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 2, 28 29 30 31 32 33 34 35 36 3, 38 39 40 41 42 43 44 45 46 4, 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 6, 68 69 70 71 72 73 74 75 *indicates

66.012' 64.620' 62.790. 61.146*

25547.488 47.034 46.625 46.131 45.664 45.281 44.851 44.41, 43.963 43.615 43.180 42.757 42.328 41.932 41.538 41.167 40.766 40.369 39.999 39.622 39.250 38.851 38.49, 38.129 37.747 37.414 37.035 36.656* 36.330 35.952

35.617' 35.203 34.@3,* 34.513' 34.094' 33.760 33.360 32.992

25584.280' 84.280. 84.505 84.818 85.185 85.692 86.195 86.756 87.358

32.5,,* 32.112* 31.65,* 31.201' 30.632' 30.019' 29.319 28.523 27.554 26.403 25.039 23.389 21.505 19.302 17.014 14.235

25536.656" 35.617' 34.887' 34.513' 34.094* 33.630 33.19,

87.959

25588.626 89.27,

25532.577* 32.279 32.112* 31.782 31.65,' 31.444 31.197'

89.951

90.665 91.368 92.076 92.793 93.501 94.216 94.936 95.621 96.429 96.928

30.632.

26162.027 62.469 62.932 63.398 63.859 64.324 64.793 65.263 65.736 66.207 66.680 67.153 67.626 68.095 68.570 69.044 69.518 69.993. 70.46, 70.939 71.414 71.88, 72.360 72.836 73,294 73.780 74.252 14.727 75.201 75.674 76.148 76.618 77.093 77.562 78.035 78.506 78.974 79,447 79.912 80.38 80.844' 81.308 81.773 82.232 82.695 83.147 83.596 84.044 84.488 84.925 85.354 85.776 86.190 86.589 86.982 87.356 87.709 88.041 88.338 88.615 88.828 26189.076* 89.076. 89.076' 88.984 88.680 88.234 87.517 86.500 85.124 83.354 80.844*

30.338 75.649 30.019’

of the l- 1 Band

26161.103 60.648 60.191 59.744 59.296 58.848 58.407 47.964 57.521 57.079 56.639 56.200 55.767 55.327 54.888 54,455 54.015 53.578 53.144 52.708 52.272 51.840 51.405 SO.969 50.536 50.101 49.668 49.236 48.802 48.368 47.935 47.502 47.067 46.632 46.200 45.766 45.332 44.898 44.463 44.02, 43.591 43.160 42.715 42.277 41.834 41.396 40.944 40.494 40.037 39.568 39.122 38.658 38.177 37.686 37.198 36.69, 36.167 35.625 35.064 34.472 26133.840 33.173 32.440 31.630 30.751 29.744 28.560 27.209 25.599 23.692 21.431 18.599 15.413 11.216

29.649

a double or blended

line

Note: Seventh column, line 8, should read 57.964; sixth column, line 40. should read 80.380.

TABLE Vacuum -R(J)

J

Wavenumbers p(J)

of the 1-2 Band R(J)

IV Vacuum

Wavenumbers

R(J)

i

of the 2-2

P(J)

P(J) 26258.137

2

57.713

3 4

57.251

5

56.350

6 7

55.894

56.792

55.442

B

54.984

9

54.531

10

54.074

11

53.619

12

64.454

53.160

13

64.905

52.700

14

65.357

52.250

15

65.807

51.796

16

66.244

51.333

17

66.865

18

67.132

50.417

19

67.585

49.967

20

68.028

49.505

21

68.470

49.045

22

68.911

48.585

21

69.350

48.125

24

69.801

47.671

25

70.217 70.677

47.208

71.116

46.283

26 27 28 29

71.552 71.990

30

72.427 72.858

31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

50.874

46.749

73.293 73.717 74.143 74.578 74.989 75.403 75.804 76.212 76.598 76.919 77.309 77.613 77.905 78.119 78.119 77.905 77.613

26289.937 88.073

77.309 76.598 74.576

26X5.372’

86.606 85.948

42.558’ 40.157’

85.711 85.463

53

38.593’ 37.420’

85.463 85.711

54 55 56

36.299 35.415’ 34.857

85.948 86.261 86.606

57 58

34.261’ 33.617’

86.923 87.318 26287.686

59 60 61 62

33.071’ 26232.521 31.975 31.499

88.073 88.439 88.837

63 64 65 66

89.212 89.578 89.937 90.285

67 68

29.989 29.475 28.967 28.448 27.917 27.390 X.839 26.250 25.678 25.047 24.400 23.671

90.653 91.024

69 70 71 72

91.627

73

74 75 76 77

Note: column,

Band

_._~ _

Third column, line 12. should read 52.965: line fifty-one, should read 31.739. 325

third column.

line 19. should

read 50.242:

sixth

326

JONES AND MC LEAN TABLE V Rotational Constants for BO+ and X,0+ States of BiF (cm-l) V’

x10+

BO+

1*

0* B" Y

0.22927(3)

2*

0.22780(3)

0.22633(3)

3** 0.224714)

4" 0.2233(Z)

5**

6**

0.2223(5) 0.2206(3)

D" x 107 "

1.92(24)

2.14(12)

2.23(13)

1.8(l)

2.0(l)

2.50(l)

2.6(l)

B"t "

0.22924

0.22774

0.22623

0.22473

0.22322

0.22173

0.22022

B' "

0.2299(l)

0.2284(l)

0.2262(l)

0.222(l)

0.223(l)

0.223(l)

0.222(l)

rJ; x lo7

5.0(Z)

3.611)

3.3(l)

1.3(Z)

2.5(Z)

2.9(l)

*Calculated

using Pwge

-2.8(9)

Prcqram

**From Single Band Analysis tCalculated from Data of Kuijpers P. and Dymanus A., Chem. Phys. 24, 97 (1977). Number(s) in parentheses are the uncertainty in the last digit(srthat correspond to one standard deviation Note: Third column, last line, should read 4.7(3); fourth column, last line, should read 3.5(2); fifth column. last line, should read 2.3(3).

where BA and DA are the unperturbed rotational constants of the upper state. A plot of&(J) VSJ for the O-O band is shown in Fig. 4. An analogous relationship (4*) exists for the extra lines (f&(J)), except Bh is now replaced by B6, the unperturbed B value of the perturbing level. On combining Eqs. (4) and (4*), we arrive at the relationship f&J)

+f&(J)

= (BI, + B;) + 2B”.

(5)

Since Bh and B" had previously been determined a calculation of Bb was possible. Using this method, Bb values of 0.201 and 0.196 cm-’ were obtained for the perturbations at u’ = 0 (J = 48) and u’ = 2 (J = 51), respectively. A summary of the positions of maximum perturbation in each of the upper vibrational levels is given in Table VII. A plot of the rotational energy levels against J(J + 1) is shown in Fig. 5, the solid lines representing the vibrational levels of the BO+ state. The positions of maximum perturbation, i.e., the points of intersection between the BO+ and perturbing state, are indicated. Rotational levels of this state are given by the dotted lines. BL values as calculated from Eq. (5) were used to generate the lines passing through u’ = 0 (J = 48) and v’ = 2 (J = 51). Parallel lines were then drawn to account for as many of the perturbations as possible. It was found that this could be accomplished using a AG value of about 250 cm-‘. It is evident that not all the perturbations can be assigned to a single perturbing state (Fig. 5) indicating that at least two different perturbing states are involved. Vibrational perturbations are believed responsible for a shift between expected and observed positions of the band origins in the 3-3, 4-4, and 6-6 bands. Erratic line intensities in the first 15 lines of the 3-3 band are indicative of such perturbations. These interactions are characteristic of homogenous perturbations, i.e., at least one of the perturbing states has 0+ symmetry. Of the known lower lying states only the AO+ state has been studied in sufficient detail to consider it as a possibility for the observed perturbing state. The known molecular parameters are w, = 381 cm-‘, w,x, = 3.00 cm-‘, w,y, = 0.01 cm-l B,

BO+-X,0+ TRANSITION

OF BiF

327

328

JONES AND MC LEAN TABLE VI Table of Molecular Parameters (cm-l)

x,0+

BO+

Te

0

26000.30

we

512.9

626.8

'exe

2.35

6.6

'e

0.2300, (0.22999)*

0.231

ae

1.47 x 10-3 (1.50 x 10‘3)*

2xlo-3

1.92 x lO-7 (1.85 x 10-7)*

5.0 x lo-7

2.052 x 1O-8 cm

2.05 x lO-8 cm

Do r e "00

(1. 7 x 10‘3)'

26056.12

* Calculated from Data of Kuijpers P. and Dymanus A., Chem Phys. 24, 97 (1977). 'Calculated from Eq. (2).

= 0.2101 cm-’ and cx, = 8 x lo-* cm-’ (6,9). An energy of 3041 cm-’ separates the respective potential minima. Vibrational levels above u = 8 can thus interact with the B O+levels. Although the B values of the AO+ state are of the same magnitude as those calculated from Eq. (5), the (Y,value of 1.3 x 10e3 cm-’ as derived from Fig. 5 differs somewhat; however, it should be noted that the B6 values were determined to only three significant figures. Using the above data, the vibrational quanta of the A O+ state are too large compared to those predicted from Fig. 5. We have recently photographed the A 0+-X,0+system in emission and have ob-

CM-' 0 230

E

l

-z,,, ;'

\

:

.

l

:

0.220

. .. ...a..... . . .*.....

:.

.

. * . cm

*. --.

l

'.

-.

.

C .

0210-

.

.

..

. : . . I . l

0200-

I

'1:48' 0

2

J:79 4

6

J:117 8

1O-3X

10

12

14

(J+1/2j2

FIG. 3. Plot of AzF’/4(J + l/2) vs. (J + l/2)* for the O-O band.

16

BO+-X,0+ TRANSITION

OF BiF

329

n

FIG. 4. Plot off,,(J)

andf*,,(J)

vs. J for the O-O band.

served no structure resembling that found in the BO+ system for levels in which ~3’> 8, further indicating that the A O+ state probably is not the perturbing state indicated in Fig. 5. Information on the other reported nearby states is too sketchy to convincingly discuss their possible involvement. Table VIII gives the various electronic configurations of BiF, involving a one electron jump, and the resulting terms. Configuration I is that of the ground state, configurations II and III involve the transition of a bonding electron to antibonding orbital, thereby increasing r, and decreasing B,. Configuration IV involves an antibonding-antibonding transition and again a smaller B, relative to the ground state is expected. The vibrational frequency of the BO+ state is much larger than the three neighboring states (AO+. 381 cm-‘; A’. 294; A,, 399) TABLE VII Position of Maximum Perturbations

v

J

a

*

in BO+ State

48, 78, 117*

1

73: 82*

2

51, 78*

3

14* (

4

50

5

43*

6

60*

extrapolated

values.

74*

JONES AND MC LEAN

FIG. 5. Term value plot of BO+ state showing known (clear stars) and extrapolated (darken stars) positions of the perturbations. Dotted lines indicate a possible rotational energy diagram for the perturbing state.

and the re values of the X,0+ and BO+ states are almost identical. This suggests the Rydberg configuration V is the most likely, to account for the BO+ state. Assuming the Rydberg series converges to the ground state of the BiF+ molecule, the force constants of the BO+ and the X211 ground state of BiF+ should be identical. Unfortunately, the BiF+ molecule has not been reported. However, the isoelectronic molecule BiO has been studied. The agreement is remarkable: TABLE VIII Electronic Configurations I

2 . . . . X3,-, (zo)*(yo)*(~~)4(~~)*(“~)

II

(20)

III

(zu)

IV V

of BiF

2 2

(yo) (yo)

2 2

(wTl)4(xL7)(“n) (wT)3(x~)2(“n)

3

....

3

ni,

‘Z+

3z+,

3,-

*. %,,

1,

3 . . . 3,.

~zo~*~y~~*~~~~~~~o~*(“~~(“~)

‘A, 1 n

(zo)*(~~)*(wn)~(xo)*(vn)(nso, npo, npn ... C311,d', and other Rydberg states.

t

1

a,

) ..,

‘I+.

‘z-

B3n, C’II,

BO+-X,0+ TRANSITION

OF BiF

331

k = 0.40 Mdynelcm for the BO+ state as compared to k = 0.42 Mdynekm calculated from data given for the ground state of BiO (24 ). The analysis of additional band systems of BiF is currently in progress and we hope that this will eventually help to identify the perturbing states found in the BO+-X,0+ system. ACKNOWLEDGMENTS We are indebted to Dr. G. Krishnamurty for many helpful discussions. We thank Dr. J. Wasson for his valuable assistance in using the computer programs, and acknowledge the use of the merge program prepared by Dr. R. Vasudev. Thanks are also due to Dr. M. Rujimethabhas for obtaining the initial spectra. We acknowledge the kind permission of Dr. A. E. Douglas in allowing us to use the facilities at the National Research Council in Ottawa and the assistance of F. Alberti in obtaining some of the spectra. An Operating grant from the Natural Sciences and Engineering Research Council to W.E.J. and a Dalhousie Graduate Scholarship to T.D.M. are acknowledged.

RECEIVED:

August I, 1979 REFERENCES

1. A. E. DOUGLAS AND W. E. JONES, Canad. J. Phys. 44, 2251-2258 (1%6).

2. 3. 4. 5. 6. 7. 8. 9.

IO. II. 12.

13. 14. 15. 16. 17.

18. 19. 20. 21.

22. 23. 24.

25. 26.

W. E. JONES, Canad. J. Phys. 45,21-26(1%7). R. COLIN, 3. DEVILLERS,AND F. PREVOT,J. Mol. Specrrosc. b&230-235 (1972). D. S. LIU AND W. E. JONES, Canad. J. Phys. 50, 1230-1251 (1972). D. K. W. WANG. W. E. JONES, F. PREVOT, AND R. COLIN, J. Mol. Spectrosc. 49, 377-387 (1974). H. G. HOWELL, Proc. Roy. Sot. Ser. A 155, l41- 150 (1936). F. MORGAN, Phys. Rev. 49,41-46 (1936). G. D. ROCHESTER,Phys. Rev. 51, 486-490 (1937). T. A. RAO AND P. T. RAO, Canad. J. Phys. 40, 1077-1085 (1%2). T. A. RAO AND P. T. RAO, Ind. J. Phys. 36, 85-92 (1%2). K. M. RAO AND P. T. RAO, Ind. J. Phys. 39, 572-579 (1%5). P. KUIJPERS AND A. DYMANUS, Chem. Phys. 24,97- 103 (1977). K. C. JOSHI, Proc. Phys. Sot. 78, 610-613 (1961). B. S. MOHANTY, D. K. RAI, K. N. UPADHYA. AND N. L. SINGH. J. Phys. B 1,523-524 (1%8). A. K. CHAUDRY,K. N. UPADHYA,D. K. RAI,ANDB. S. MoHANTY,.I.P~~.~. B 1,1223-1224(1%8). A. K. CHAUDRY, K. N. UPADHYA, AND D. K. RAI, J. Phys. B. 2,628-630 (1969). M. N. AVASTHI, Spectrosc. Lerr. 3 (7), 157-159 (1970). P. S. MURTY, D. V. RAO, Y. P. REDDY, AND P. T. RAO, Spectrosc. Left. S(4), 217-221 (1975). M. M. PAT-EL AND P. S. NARAYANAN, Ind. 1. Pure Appl. Phys. 5.223-226 (1967). G. HERZBERG. “Spectra of Diatomic Molecules,” 2nd ed., Van Nostrand, New York, 1950. I. KOVACS. “Rotational Structure in the Spectra of Diatomic Molecules.” Hilger. London, 1969. D. L. ALBRITTON, W. J. HARROP, A. L. SCHMELTEKOPF. R. N. ZARE. AND E. L. CROW, J. Mol. Spectrosc. 46,67-88 (1973). A. E. DOUGLAS AND M. FRANKOWIAK, Canad. J. Phys. 40, 832-839 (1%2). R. F. BARROW,W. J. M. GISSANE, AND D. RICHARDS.Proc. RI)?. SW. Ser A 300, 469-486 ( 1967) D. L. ALBRITTON, A. L. SCHMELTEKOPF, AND R. N. ZARE, “Modem Spectroscopy, Modern Research II,” (K. Narahari Rao, Ed.), pp. l-67, Academic Press, New York. 1976. D. L. ALBRITTON, A. L. SCHMELTEKOPF, AND R. N. ZARE, J. Mol. Spectrosc. 46,132- 156( 1977).