Hybrid fs/ps CARS measurements of vibrationally excited N₂(V) and H₂(V) in DC glow discharges

Vibrationally excited N₂ (N₂(v)) and H₂ (H₂(v)) produced in N₂ /H₂ DC glow discharges were characterized by hybrid fs/ps coherent anti-Stokes Raman scattering (CARS). The hybrid CARS system was developed to target both the N₂ and H₂ ro-vibrational Raman transitions. In addition, the gas temperature was measured from the N₂ pure-rotational spectra. The vibrational population distributions of the N₂ molecule were calculated based on the vibrational temperatures. Measurements were performed near the anode with different H₂ /N₂ ratios at 75 torr. It is observed that the addition of H₂ reduces the N₂ vibrational temperature and increases the gas temperature. The gas heating is mainly due to the vibration-translation (V-T) relaxation between N₂(v) and H₂ . Moreover, the N₂(v) population stays relatively constant as the H₂ concentration increases from 20% to 75%, while the H₂(v) population increases. This suggests that vibration-vibration (V-V^′ ) transfer between H₂(v) and N₂ enhances the generation of N₂(v).