Using this page you can plot rotation diagrams for a few atomic species. All you need to do is give a list of line fluxes in units of W/m². Need to convert units? Maybe my unit converter can help. A second column of numbers, separated by spaces, commas or tabs, is taken as the uncertainty on the flux, but can be omitted. Lines of text or blank lines are just ignored.

Data are from the CDMS and all available transitions are included. Equations from Justtanont et al., 2000 are applied to the fluxes to derive level populations, and a least squares fit is determined to derive the rotational temperature. You can fit different J-ranges separately by putting a "/" as the final column in the data at the point you want to separate the fit at. Any number of split points can be defined.