Hybrid fs/ps CARS Measurements of Vibrationally Excited N 2 ( v ) and H 2 ( 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).