In this study the interaction of a rf nitrogen plasma source with hydride precursors, during the chemical beam epitaxy of III-V dilute nitrides is investigated. For this purpose the rf nitrogen plasma cavity spectrum is monitored in real time. During the growth of III-V dilute nitrides and upon introduction of hydride precursors, such as AsH3, in the chemical beam epitaxy chamber the cavity plasma spectrum is marked by the appearance of a sharp emission at 656 nm, the energy of which corresponds to the first term of the Balmer series of the hydrogen atom, suggesting the retro diffusion of residual hydrogen in the plasma cavity and the formation of atomic hydrogen species. The evolution of the intensity of this peak as a function of rf plasma source parameters and hydrogen flow is investigated in an attempt to offer practical means of minimizing the possible effects of hydrogen atoms on the fabricated material. Improved optical properties as attested by the sharp photoluminescence (PL) emissions in as-grown samples and minimal thermal annealing induced PL energy shifts are reported for GaAsN epilayers grown under low H2N2 partial pressure conditions. © 2005 American Vacuum Society.