We report the absolute column densities of gas phase C6H6 and upper limits on absolute C4H2 and C2H3 concentrations in a hot filament diamond chemical vapor deposition (CVD) reactor. The steady state density of C6H6 is monitored as a function of C2H2 and H-2 input fractions. The C6H6 column density is a quadratic function of input C2H2 fraction at low C2H2 fractions. Above a critical C2H2 input fraction, the C6H6 column density becomes independent of C2H2 input fraction. The column density of gas phase C6H6 is relatively insensitive to the input H-2 fraction. The weak relationship between C6H6 and H-2 input fraction is in contradiction to the conclusion drawn from chemical kinetics modeling of diamond CVD that H-2 strongly suppresses the formation of aromatic species under diamond CVD conditions. Moreover, comparison of C6H6 column densities with previously measured CH3 column densities under similar conditions indicate that a comparable fraction of gas phase carbon atoms in the steady state are incorporated in C6H6 as are incorporated in the growth species CH3.