The arc spectrum of silicon has been reinvestigated from 1976 to 12 270 Å by using plane and concave grating spectrographs and Fabry–Perot interferometers. Electrodeless discharge lamps containing silicon–halogen compounds, and a silicon arc operated in argon at reduced pressure, were used to obtain measurements on 395 wavelengths, 192 of them interferometric. The total number of newly observed lines is 179, and the number of new classifications 174. Forty-two new even levels were established, principally from the 3s2 3p np (n = 6, 7) and 3s2 3p nf (n = 5, 6, 7) configurations. With the aid of vacuum-ultraviolet data provided by A. G. Shenstone, 38 new odd levels were found. The interferometric and grating investigation has led to the calculation of 92 provisional Ritz standards between 1580 and 2000 Å with uncertainties of less than 0.002 Å. The new wavelength data have also made possible the identification of 76 previously unidentified solar lines as due to Si i. Nineteen other solar lines have been identified as possibly attributable to Si i. A limit of 65 747.5±0.6 cm−1 has been derived for the Si ii level
from the nd and nf level series. This corresponds to an ionization potential of 8.15116±0.00008 V.
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The following symbols with the meanings indicated have been used to characterize the lines: h = slightly hazy; H = more hazy; HH = very hazy; r = narrow reversal; R = wide reversal; r(v) = reversal toward violet side of line; r(r) = reversal toward red side of line; S = sharp; p = polar; d = diffuse; B = broad.
The following letters indicate the spectroscopic source from which the data for the given wavelength were obtained: C = silicon tetrachloride electrodeless discharge lamp; I = silicon tetraiodide electrodeless discharge lamp; A = silicon–argon arc source; S = vacuum-ultraviolet are source (Shenstone’s data).
Letters in this column identify lines found also in the solar spectrum as discussed in See. VI. The letters have the following meanings: P = previously identified in sun; N = newly identified in sun; M = masked in sun.
All the wavelength values with two places behind the decimal are the result of grating measurements. All wavelengths, other than Shenstone’s, with more than two places behind the decimal are the result of interferometric measurements except those indicated by the superscript j, which are grating measurements with uncertainties less than 0.01 Å.
Wavenumber uncertainty.
This column contains the difference between the wavenumber as observed, and the wavenumber as calculated using the best level values obtained for that source listed in column 2. Consequently, these entries show the internal consistency of the data from any given source, but do not reveal intersource shifts.
The numbers in this column are the code numbers of the levels given in Tables III and IV. The ° superscript is used to indicate an odd level.
When a classification is given but no value appears in this column, the line is the only one supporting one of the combining levels in the source of col. 2.
This line fits very well the transition 3–83.1°. However, since the two preceding members of this series were absent, this designation was rejected and the agreement considered to be accidental.
Grating measurement (see footnote d).
This is a forbidden transition, first noted by Shenstone and probably due to the electric fields in the sources.
For completeness, Shenstone’s intensities are also given for ultraviolet lines observed by us.
In a few cases the wavelength value from the iodide source is to be preferred over that from the chloride source, because in the latter source the lines were obscured by bands or other lines.
The letter in this column denotes the spectroscopic source of the data upon which the corresponding level value is based. C = silicon tetrachloride electrodeless discharge lamp; I = silicon tetraiodide electrodeless discharge lamp; A = silicon–argon arc source.
See Ref. 4.
Fowler gives the same designation, see Ref. 2.
A parenthesis about a level value indicates that the level has been established by a single combination.
The letter in this column denotes the spectroscopic source of the data upon which the corresponding level value is based. C = silicon tetrachloride electrodeless discharge lamp; I = silicon tetraiodide electrodeless discharge lamp; A = silicon–argon arc source; S = vacuum-ultraviolet arc source (Shenstone’s data).
See Ref. 4.
See Ref. 2.
A parenthesis about a level value indicates that the level has been established by a single combination.
See Ref. 17.
n signifies the principal quantum numbers of the levels used in the calculation.
In cases for which the number of levels minus the number of parameters equals one, the standard deviation is meaningless.
Table VI
Calculated wavelengths of some vacuum ultraviolet lines of Si i.
The following symbols with the meanings indicated have been used to characterize the lines: h = slightly hazy; H = more hazy; HH = very hazy; r = narrow reversal; R = wide reversal; r(v) = reversal toward violet side of line; r(r) = reversal toward red side of line; S = sharp; p = polar; d = diffuse; B = broad.
The following letters indicate the spectroscopic source from which the data for the given wavelength were obtained: C = silicon tetrachloride electrodeless discharge lamp; I = silicon tetraiodide electrodeless discharge lamp; A = silicon–argon arc source; S = vacuum-ultraviolet are source (Shenstone’s data).
Letters in this column identify lines found also in the solar spectrum as discussed in See. VI. The letters have the following meanings: P = previously identified in sun; N = newly identified in sun; M = masked in sun.
All the wavelength values with two places behind the decimal are the result of grating measurements. All wavelengths, other than Shenstone’s, with more than two places behind the decimal are the result of interferometric measurements except those indicated by the superscript j, which are grating measurements with uncertainties less than 0.01 Å.
Wavenumber uncertainty.
This column contains the difference between the wavenumber as observed, and the wavenumber as calculated using the best level values obtained for that source listed in column 2. Consequently, these entries show the internal consistency of the data from any given source, but do not reveal intersource shifts.
The numbers in this column are the code numbers of the levels given in Tables III and IV. The ° superscript is used to indicate an odd level.
When a classification is given but no value appears in this column, the line is the only one supporting one of the combining levels in the source of col. 2.
This line fits very well the transition 3–83.1°. However, since the two preceding members of this series were absent, this designation was rejected and the agreement considered to be accidental.
Grating measurement (see footnote d).
This is a forbidden transition, first noted by Shenstone and probably due to the electric fields in the sources.
For completeness, Shenstone’s intensities are also given for ultraviolet lines observed by us.
In a few cases the wavelength value from the iodide source is to be preferred over that from the chloride source, because in the latter source the lines were obscured by bands or other lines.
The letter in this column denotes the spectroscopic source of the data upon which the corresponding level value is based. C = silicon tetrachloride electrodeless discharge lamp; I = silicon tetraiodide electrodeless discharge lamp; A = silicon–argon arc source.
See Ref. 4.
Fowler gives the same designation, see Ref. 2.
A parenthesis about a level value indicates that the level has been established by a single combination.
The letter in this column denotes the spectroscopic source of the data upon which the corresponding level value is based. C = silicon tetrachloride electrodeless discharge lamp; I = silicon tetraiodide electrodeless discharge lamp; A = silicon–argon arc source; S = vacuum-ultraviolet arc source (Shenstone’s data).
See Ref. 4.
See Ref. 2.
A parenthesis about a level value indicates that the level has been established by a single combination.
See Ref. 17.
n signifies the principal quantum numbers of the levels used in the calculation.
In cases for which the number of levels minus the number of parameters equals one, the standard deviation is meaningless.
Table VI
Calculated wavelengths of some vacuum ultraviolet lines of Si i.