Arc discharge d.c. plasma CVD has been established as an interesting and promising method for the production of diamond films. A configuration with a stabilized discharge, well suited to different optical plasma diagnostic methods, has been used. Typical process parameters have been varied and the resulting films analyzed using scanning electron microscopy and Raman spectroscopy as the usual methods. To obtain more insight into the basic phenomena involved, the film properties have been related to spectroscopic data describing plasma properties. In particular, the strong dependence of the film properties from the distance of the substrate to the arc can be explained by the radial temperature distribution within the arc plasma.