The column densities of several molecular radicals are measured in an oxyacetylene torch flame during the growth of diamond films. The column densities of CH,C2,CN, and OH radicals are determined by highly sensitive absorption spectroscopy. The radical densities are measured as a function of position in the flame for different fuel/oxidant ratios. The growth of diamond is confirmed by scanning electron microscopy and Raman spectroscopy. Of the four radicals measured, theC2and CH densities are the most correlated with diamond growth. The measured densities are compared with numerical flame models. ©1997 American Institute of Physics.