A parallel ‐ plate, low ‐ pressure plasma for fundamental nanodusty plasma re- search is used to grow hydrogenated amorphous carbon nanoparticles using an argon ‐ acetylene gas mixture. The particles stay confined in the volume of the argon plasma after turning off the C H 2 2 gas flow and the effects of pro- longed treatment with noble gas (Ar) and reactive gas mixtures (Ar/ H 2, Ar/ D 2, or Ar/ O 2) are investigated using in situ infrared absorption spectroscopy. Additionally, ex situ scanning electron microscopy imaging of extracted na- noparticles is used to analyze their size and surface morphology. In 45 min of argon treatment, a size increase of about 50% is seen together with a decrease in sp CH x 2 bonds and an increase in C ═ O bonds, indicating incorporation of oxygen from gas impurities into the particle material. All reactive gas mixtures lead to the expected etching of the nanoparticle material without any ex- change reactions between gas ‐ phase deuterium and surface ‐ bonded hydrogen atoms. These results are important for in situ studies of nanoparticle clouds such as dust density wave diagnostics, but they also provide fundamental informa- tion about plasma interaction with a ‐ C:H material
