Observations of t h e CO I111 52 and 88vm l i n e s and t h e CN 1111 57pm line have been made a t 6 p o s i t i o n s and t h e [Ne I111 36pm l i n e a t 4 p o s i t i o n s i n the Orion Nebula t o probe its ionization s t r u c t u r e . The measurements, made w i t h a -40" diameter beam, were spaced every 45" i n a l i n e south from and including t h e Trapezium. 36.01 3k0.004um. c a l c u l a t e d and compared t o o t h e r r a d i o and optical observations. component and two component

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... (bar plus halo) spherical models were c a l c u l a t e d f o r e x c i t i n g stars with e f f e c t i v e temperatures of 37-40,OOOK and l o g g 14.0 and 4.5. Both t h e new i n f r a r e d observations and the v i s i b l e l i n e measurements of oxygen and n i t r o g e n r e q u i r e Teff < 37,OOOK. a model with Teff I 39,OOOK, which is more c o n s i s t e n t w i t h that i n f e r r e d from t h e r a d i o f l u x or spectral type. effects o f d u s t on t h e s t e l l a r r a d i a t i o n f i e l d , but are probably due t o i n a c c u r a c i e s i n t h e assumed s t e l l a r spectrum. almost twice the N+/O+ r a t i o . and Ne/H=1.3~10-~. is h a l f s o l a r i n abundance. i o n i z a t i o n bar r e s u l t s from an increase i n column d e p t h rather than from a l o c a l d e n s i t y enhancement. The wavelength of t h e [Ne 1111 l i n e was measured t o be Electron d e n s i t i e s and abundance r a t i o s o f N++/O++ have been Detailed one However, the doubly i o n i z e d neon r e q u i r e s These d i f f e r e n c e s i n Teff are n o t due t o The observed N++/O++ r a t i o is Our b e s t f i t models give N / H = 8 . 4~1 0 -~, O / H = 4 . 0~1 0 -~, Thus neon and n i t r o g e n are approximately s o l a r , but oxygen From t h e i n f r a r e d O++ l i n e s we conclude t h a t t h e