ISM PARAMETERS IN THE NORMAL GALAXY NGC-5713

We report ISO Long Wavelength Spectrometer (LWS) observations of the S bc galaxy NGC 5713. We have obtained strong detections of the fine-str ucture forbidden transitions [CII] 158 mu m, [OI] 63 mu m, and [OIII] 88 mu m, and significant upper limits for [NII] 122 mu m, [OIII] 52 mu m, and [NIII] 57 mu m, and have measured the galaxy's FIR dust contin uum. These observations represent the first FIR line survey of a nearl y normal galaxy and allow us to make comparisons with COBE results for the Milky Way, and with KAO observations of LR-bright starburst galax ies. We find that NGC 5713 displays a fairly high [CII]/FIR ratio (sim ilar to 0.7%). Under the assumption that the disk emission is dominate d by photodissociated molecular gas, we model the FIR continuum and th e [CII] and [OI] line fluxes to derive the density of the warm atomic gas surrounding molecular clouds and the UV flux incident on the cloud s. In this model, we find higher densities and lower UV fluxes in NGC 5713 than are typical for starburst galaxies, but higher UV fluxes tha n suggested for the disks of NGC 6946 and the Milky Way. We also discu ss alternative origins for the strong [CII] emission, such as from a d iffuse component of cold HI.