RELATIVE EMISSION-LINE STRENGTHS FOR THE 146 AND 63 MICRON TRANSITIONS IN O-I AND A COMPARISON WITH FAR-INFRARED OBSERVATIONS OF PHOTODISSOCIATION REGIONS

Theoretical O I density-sensitive emission-line ratios R = 3)P0-2s(2)2 p4(3)P1)/I(2s(2)2p4(3)P1-2s(2)2p4(3)P2) = I(146 mum)/I(63 mum) are pre sented for a range of temperatures (T = 100-10,000 K), neutral hydroge n densities (N(H) = 10(-2) to 10(7) cm-3) and radiation fields (G0 = 1 -10(6)) applicable to both photo-dissociation regions (PDRs) and H II regions and the diffuse ionized medium (DIM). The observed values of R for several PDRs, measured from far-infrared spectra obtained with th e Kuiper Airborne Observatory, imply hydrogen densities which are in g ood agreement with those determined using other methods. This provides observational support for the validity of the theoretical O I line ra tios, and hence the atomic data used in their derivation.