Current Results and Future Prospects

The spectra of dilute molecular gases in astrophysics arise in material far out of thermodynamical equilibrium (non-LTE), often in inhomogeneous atmospheres where Doppler motions from kinematical gradients and turbulence are large compared with thermal motions. Thus line intensities contain information about density and temperature as well as abundances, and line profiles probe the structure of the atmosphere. However, the theoretical description of the atmosphere can be extremely complicated and can make enormous demands for molecular data. Improvements in angular resolution and the possibility to make sensitive spectroscopic measurements at mid-infrared and submillimeter wavelengths pose new challenges for theoretical models.