Light emanating from ac arcs operating on 60-Hz power exhibits a 120-Hz modulation of intensity. Although time-averaged spectra of such arcs are usually reported, the instantaneous light spectrum and its dependence on the oscillating plasma temperature is a more valuable source of spectroscopic information. An experimental technique is described for scanning the spectrum of an ac discharge at any fixed phase in the arc operating cycle. Spectra were recorded at phases corresponding to maximum and minimum light output for a pure Hg arc, a Hg–Na, Sc, Th metal-iodide arc, a Hg high-pressure Na arc, and a Hg–SnI2 arc. Intensity ratios Imax/Imin of spectral lines generally increased with increasing upper-state energy. Many of the dominant lines also exhibited sizable changes of line profile with variations of phase. In the Hg–Na, Sc, Th metal-iodide arc, the intensity variations of optically thin lines were used to obtain estimates of upper-state energies and relative gA values of some Th lines for which these quantities were previously unknown.
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Wavelength classifications from Zalubas, Ref. 11. gA values from Corliss and Bozman, Ref. 12.
Table VI
Upper-state energies E and relative gA values of Th i determined from measurements of Imax/Imin and relative Imin. The gA values are normalized to those listed for Th in the tables of Corliss and Bozman (Ref. 12).
Wavelength (Å)
Imax
Imin
Imax/Imin
E (103 cm−1)
gA (108 sec−1)
3397.5
13.4
2.80
4.79
34.5
3
3398.5
14.8
3.79
3.91
31.0
2
3413.0
14.5
2.86
5.07
35.5
5
3451.7
8.99
1.75
5.14
35.5
3
3486.5
12.6
2.63
4.79
34.5
3
3592.8
10.9
1.82
5.99
38.5
7
3608.4
9.57
1.55
6.17
39.0
7
3632.8
9.52
1.75
5.44
36.5
4
3634.6
14.4
2.78
5.18
36.0
5
3635.9
14.8
2.72
5.44
36.5
6
3670.0
14.2
2.40
5.92
38.0
9
3682.5
7.53
2.29
3.29
28.0
0.4
3737.5
7.83
2.04
3.84
31.0
0.9
3742.9
8.71
2.38
3.67
30.0
0.8
3757.7
10.9
2.08
5.24
36.0
4
3776.3
6.75
1.49
4.53
33.5
1
3781.0
6.61
1.94
3.41
29.0
0.5
3811.0
7.40
1.82
4.07
32.0
1
3817.5
3.79
0.54
7.02
41.0
5
3820.8
6.97
1.86
3.75
30.5
0.8
3825.1
10.3
1.69
6.09
38.5
7
3869.7
6.94
1.73
4.01
31.5
1
3895.4
13.8
3.15
4.38
33.0
3
3903.1
7.54
1.86
4.05
31.5
1
3967.4
12.3
3.45
3.57
29.5
1
3980.1
7.69
1.31
5.87
38.0
5
4001.1
6.99
1.75
3.99
31.5
1
4008.2
11.2
2.84
3.94
31.5
2
3994.5
10.2
0.21
48.5—Probably Th ii not Th i
Tables (6)
Table I
Ratios of maximum to minimum spectral intensities in a vertically operating Hg arc. The quantity E is the upper-state energy.
Line (Å)
Imax/Imin
E (cm−1)
3650
2.7
71 431
5770
7.1
71 396
5791
6.7
71 333
4078
4.6
63 928
5461
1.9
62 350
4358
2.2
62 350
4046
2.2
62 350
Continuum
5
⋯
Photocell (eye response)
5.2
⋯
Table II
Ratios of maximum to minimum spectral intensities in a vertically operating Hg–Na, Sc, Th metal-iodide arc.
Line (Å)
Imax/Imin
E (cm−1)
5461 Hg
18
62 350
4165 Sc
5.8
40 028
5356 Sc
4.4
33 707
5482 Sc
4.2
33 279
5672 Sc
3.1
29 304
4493 Th
3.3
22 249
5761 Th
2.5
17 355
5804 Th
2.2
17 224
Na D
1.9
17 000
Photocell (eye response)
2.7
Table III
Ratios of maximum to minimum spectral intensities in a vertically operating Hg high-pressure Na arc.
Line (Å)
Imax/Imin
E (cm−1)
5461 Hg
>90
62 350
4983 Na
8.8
37 037
5154 Na
13
36 373
5688 Na
7.8
34 549
6161 Na
11
33 201
Na D (highly broadened)
5
17 000
Photocell (eye response)
7.1
Table IV
Ratios of maximum to minimum spectral intensities in a vertically operating Hg–SnI2 arc.
Line (Å)
Imax/Imin
E (cm−1)
3650 Hg
16
71 431
4047 Hg
8.4
62 350
4358 Hg
5.6
62 350
5461 Hg
5.6
62 350
4525 Sn
4.0
39 257
3801 Sn
5.3
34 914
5632 Sn
3.4
34 914
Impurities
6104 Li
1.9
31 283
Na D
1.2
17 000
6708 Li
1.3
14 904
Continuum Features
HgI
2.2
⋯
I− free–bound
4
⋯
SnI
1.2
⋯
Photocell (eye response)
1.6
Table V
Relative intensities at phases of maximum and minimum light output for Th lines of previously known E and gA.
Wavelength classifications from Zalubas, Ref. 11. gA values from Corliss and Bozman, Ref. 12.
Table VI
Upper-state energies E and relative gA values of Th i determined from measurements of Imax/Imin and relative Imin. The gA values are normalized to those listed for Th in the tables of Corliss and Bozman (Ref. 12).
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