Energy Levels and Partition Functions from the NIST Atomic Spectra Database

nist_levels() retrieves the energy levels of an atom or ion from the NIST Atomic Spectra Database, and partition_function() computes the internal partition function of a species from its levels, as needed by cf_libs().

Usage

nist_levels(species, timeout = 120)

partition_function(levels, temperature, max_energy = Inf)

Arguments

species: A character vector of species in spectroscopic notation, such as "Ca I".
timeout: The download timeout, in seconds. Default is 120.
levels: A data frame of levels with columns species, g and energy (eV), such as returned by nist_levels().
temperature: The temperature(s), in K.
max_energy: The highest level energy included, in eV: one value, or a vector named by species. Default is Inf (all levels).

Value

nist_levels(): a tibble with one row per level and columns species, configuration, term, J, g (statistical weight) and energy (eV).

partition_function(): a tibble with the species, the temperature and the partition function, for each species and temperature.

Details

All the levels listed by the ASD are returned, including the autoionizing levels above the first ionization limit, as in the partition functions computed by the ASD; levels without a statistical weight are dropped. The partition function $$U(T) = \sum_i g_i \exp\left(-\frac{E_i}{k_B T}\right)$$ is summed over the levels given, up to max_energy. In a plasma, the ionization energy is lowered by the surrounding charges, and the levels above the lowered limit do not exist: truncating the sum there matters for atoms with many high Rydberg levels close to the limit, such as the alkali metals (see cf_libs(), which does it). Without truncation, the result equals the partition function computed by the ASD.

The results of a query are cached for the R session. Cite the database when you use these data (see nist_lines()).

Author

Christian L. Goueguel

Examples

# \donttest{
# needs an internet connection
ca <- try(nist_levels("Ca I"))
if (!inherits(ca, "try-error")) partition_function(ca, temperature = c(8000, 10000))
#> # A tibble: 2 × 3
#>   species temperature partition
#>   <chr>         <dbl>     <dbl>
#> 1 Ca I           8000      2.60
#> 2 Ca I          10000      5.69
# }