Optical emission spectroscopic (OES) measurements are acquired by collecting absolute line and continuum emission fr om a hydrogen/methane plasma (300 seem H-2, 3 sccm CH4, 40-70 torr, 1600-3200 W) used for diamond deposition. The experimental results are used in tandem with numerical modeling to infer plasma parameters of interest. Numerical solutions for a microwave chemical vapor deposition (CVD), reactor are generated by coupling solutions of the Boltzmann equation and the electron energy equation to a collisional-radiative model (CRM). Results indicate that the electron-neutral free-free emission, which depends strongly on neutral density, electron density, and electron temperature, is the dominant source of continuum emission. All numerical solutions are found to be inconsistent with the experimentally measured continuum emission. A meaningful interpretation, however, is possible if the electron-H-2 cross-section, used for calculating electron-neutral free-free continuum emission, is increased by between 4 and 20 above the momentum cross-section value. We believe that such an increase is justified because of enhanced energy exchange in electron-molecule interactions.