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AtLL Data File Format

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The data are stored in free-format files, meaning that each item is separated from the next by one or more whitespace characters but that these items do not have a fixed width. Even though the data are aligned in columns, the width of these columns may change over time without notice. So do not rely on character positions when reading these files.

Level File Format

The first line of the file gives general information about the ion.
item 1 Integer. Magic number to identify the version of the data file format. This document describes version 20210220.
item 2 Integer. The atomic number of the ion.
item 3 Integer. The ionization stage of the ion, 0 → neutral, 1 → singly ionized, etc.
items 4, 5 String. The spectrum in the usual spectroscopic notation, e.g., He II. Note that this field is only included to make the file human-readable and is not used otherwise.
item 6 Integer. The number of levels in the file.
item 7 Floating point number. The ionization potential for this ion in cm-1, or zero if the ionization potential is not known.
The remaining lines give information about each of the levels in the ion. The entries are sorted in order of increasing level energy. For all integer entries, a value -1 indicates that no legitimate value for that quantity could be determined.
item 1 Integer. The index number for this level. The line file uses this index to refer to a specific level.
item 2 String. The electronic configuration of the level.
item 3 Integer. The number used to identify this electronic configuration. Configurations are numbered sequentially with increasing energy (based on the lowest level for a given configuration). Note that this number may change from one release to the next.
item 4 String. The term of the level. Note that this field is only included to make the file human-readable and is not used otherwise.
item 5 Integer. The number used to identify this term. Terms are numbered sequentially with increasing energy (based on the lowest level for a given term). Note that this number may change from one release to the next.
item 6 Boolean. True if this level is part of the ground term.
item 7 Boolean. True if this level is metastable.
item 8 Character. An additional character used to disambiguate terms in older publications (e.g., the 'a', in the ground term a6D of Fe II). An asterisk indicates that no such identification is used for this term.
item 9 Integer. The first quantum number of the term. This represents L for LS and LK coupled levels, 2*j+1 for jK coupled levels, and 2*j1+1 for jj coupled levels.
item 10 Integer. The second quantum number of the term. This represents 2*S+1 for LS coupled levels, 2*K+1 for LK and jK coupled levels, and 2*j2+1 for jj coupled levels.
item 11 Integer. An additional quantum number used to disambiguate terms in partially filled d or f shells. It is either the seniority index used in the parentage scheme notation, or the additional index introduced in the Nielson-Koster notation. There is currently no easy way to distinguish between the two notation schemes. A value -1 indicates that this additional quantum number is not used for this term (which is the case for most terms).
items 12, 13 Integers. These two numbers indicate the range of J values associated with the level, represented as a statistical weight g = 2*J+1. Usually only one g value is associated with the level, in which case the two numbers are identical. In some cases two or more levels in a term have indistinguishable energies, in which case a single entry may be used with a range of g values: glo–ghi. In that case all levels with statistical weights glo, glo+2, ..., ghi are represented.
item 14 Integer. The parity of the wave function. A value 0 indicates even parity, and 1 indicates odd parity.
item 15 Boolean. True if the term was marked uncertain, or is unknown.
item 16 String. The coupling scheme used for the term. Allowed values are LS, LK, jK, and jj. A value ** indicates that no valid coupling scheme could be determined.
item 17 Integer. The highest value of the principal quantum number n for any of the electrons in the configuration.
item 18 Floating point number. The energy of the level in cm-1.
item 19 Floating point number. The uncertainty in the energy of the level in cm-1. In older publications this number is usually not included, in which case it was estimated from the number of significant digits printed.
item 20 Integer. A set of boolean flags in hexadecimal notation. Each bit has a specific meaning as specified below. Multiple flags can be combined using the boolean or operator.
0001 The level energy comes from a theoretical calculation.
0002 Reserved.
0004 Reserved.
0008 Reserved.
0010 Sometimes laboratory experiments cannot identify sufficient lines to connect all levels together. You then get two or more groups of levels with accurate energy differences between levels in the same group. But the energy difference between the various groups is highly uncertain (and usually comes from ab initio calculations). The energies of the levels in the group that does not include the ground level are then marked with "+v", "+w", "+x", "+y", or "+z" (so up to 6 unconnected groups are supported). This specific flag indicates that the level was marked with "+v". Note that in some papers this notation is misinterpreted as meaning: this level energy has a large uncertainty.
0020 Same as 0010, but the level was marked with "+w".
0040 Same as 0010, but the level was marked with "+x".
0080 Same as 0010, but the level was marked with "+y".
0100 Same as 0010, but the level was marked with "+z".
0200 The level energy was marked uncertain with a question mark.
0400 This is not a real level, but a superlevel representing all levels with the same principal quantum number n in hydrogenic ions.
0800 This is not a real level, but an ionization limit.
1000 This is not a valid level, and is not used in the line list. There can be many reasons why the level was marked invalid. There may be incomplete information, or some of the provided information may be wrong (e.g., the LS-J combination may be forbidden by angular momentum addition rules).
item 21 Integer. The number of the literature reference for this level.

Line File Format

The first line of the file gives general information about the ion.
item 1 Integer. Magic number to identify the version of the data file format. This document describes version 20210704.
item 2 Integer. The number of spectral lines in the file.
The remaining lines in this file are sorted in order of increasing wavelength and contain the following information.
item 1 Floating point number. The wavelength of this line in μm.
item 2 Floating point number. The uncertainty in the wavelength of this line in μm.
item 3 Floating point number. The transition probability for this line in s-1. A value of 0 indicates that the transition probability is not known.
item 4 Floating point number. The uncertainty in the transition probability for this line in s-1. A value of 0 indicates that the uncertainty is not known.
item 5 Integer. The level index for the lower level.
item 6 Integer. The level index for the upper level.
item 7 Integer. The number of the transition probability reference, or 0 if there is none.
item 8 Integer. The atomic number of the element.
item 9 Integer. The ionization stage of the ion, 0 → neutral, 1 → singly ionized, etc.
item 10 Integer. The transition type: 0 → E1, 1 → IC, 2 → M1, 3 → E2, 4 → M2, 5 → E3.
item 11 Integer. This number in hexadecimal notation contains various bits as detailed below. The numbering starts with bit 0 as the least significant bit.
bit 0 If set, flag u is set for the lower level.
bit 1 If set, flag r is set for the lower level.
bit 2 If set, flag c is set for the lower level.
bit 3 Reserved.
bit 4 If set, flag U is set for the upper level.
bit 5 If set, flag R is set for the upper level.
bit 6 If set, flag C is set for the upper level.
bit 7 Reserved.
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