PHYSICAL CONDITIONS FOR FAR-INFRARED LASER-EMISSION FROM DENSE OH MASER REGIONS

In the course of modelling OH maser emission associated with star form ing regions, an extensive regime was discovered in which substantial a nd persistent inversions in certain far-infrared (FIR) transitions wer e found. This has not previously been noted either in models or in obs ervations. The conditions required are those of H-2 number densities u p to 5 10(8) CM-3 and kinetic and local dust temperatures up to 125 K. These conditions are not significantly more extreme than those believ ed to be present in hot, dense regions of molecular gas clouds associa ted with H II regions. The transitions involved, F2 J = 7/2 --> F1 J = 9/2 and F2 J = 5/2 --> F1 J = 7/2, occur at 135 and 115 mum respectiv ely. Predicted fluxes may be detectable at present with the Kuiper Air borne Observatory and would be readily detectable with the ISO satelli te.