General description

Introduction

Written as a general purpose radiative solver, the code is built around the spectroscopy databases (HITRAN/HITEMP, GEISA, ExoMol, etc.) for molecules in their electronic ground state. Energy levels are read from tabulated databases or calculated from Dunham developments. Boltzmann, Treanor, and state specific vibrational distributions can be generated. Spectra at thermal equilibrium can be computed for all species (MOLECULES_LIST_EQUILIBRIUM). and non-equilibrium spectra can be computed for CO₂ and CO (MOLECULES_LIST_NONEQUILIBRIUM).

To fit experimental spectra, RADIS includes a LineSurvey tool, an interface with a look-up SpecDatabase to improve fitting convergence times, and a multi-slab module with a radiative transfer equation solver to reproduce line-of-sight experiments. Validation cases against existing spectral codes and experimental results from various plasma sources are included [RADIS-2018].

Features

RADIS is both an infrared line-by-line code and a post-processing library. It includes:

• Absorption and emission spectra of all [HITRAN-2020] and [ExoMol-2020] species under equilibrium calculations (MOLECULES_LIST_EQUILIBRIUM)

• Absorption and emission spectra of CO2 and CO for non-LTE calculations (see MOLECULES_LIST_NONEQUILIBRIUM )

• A common API to Different Line Databases: support of [HITRAN-2020], [HITEMP-2010], [CDSD-4000], [ExoMol-2020], [GEISA-2020] line databases (see KNOWN_DBFORMAT). The API is also compatible with the exojax code.

• Calculation of rovibrational energies of molecules, see database handling.

• Calculation of equilibrium and nonequilibrium partition functions, see database handling.

• Spatially heterogeneous spectra, see see line-of-sight

• Post-processing tools to load and compare with experimental spectra

• A Line Survey tool to identify which lines correspond to a spectral feature.

• A Matlab implementation

RADIS does not include, so far:

• Line-mixing effects and speed-dependant lineshapes. [HAPI] is a Python alternative that does it.

• Collisional-induced absorption (CIA) or emission.

• Electronic states other than electronic ground states

• Hamiltonian calculations (a private module for CO2 is available on request)

• Raman spectra (contribute in #43)

RADIS also features:

• High Performances: spectra are calculated up to several orders of magnitude faster than equivalent line-by-line codes.

• GPU Acceleration: CUDA/Vulkan GPU-powered spectrum computation for real-time and interactive use with eq_spectrum_gpu().

• In-the-browser calculations (no install needed) : see 🌱 RADIS Online.

• Automatic download of the latest HITRAN and HITEMP databases with calc_spectrum()

• Automatic testing and continuous integration tools for a reliable Open-source Development.

Thermodynamic codes

Cantera

RADIS can compute gas mixture compositions under chemical equilibrium using CANTERA (in particular the [CANTERA] equilibrate() function). Refer to get_eq_mole_fraction() for more information.

New features

RADIS is open-source, so everyone can contribute to the code development or suggest new features in our GitHub page. Read the Developer Guide to get started.