Experimental study of rotational relaxation for D2(1,12) in collisions with N2.

The rotational relaxation behavior of D₂(1,12) in a D₂–N₂ mixture was investigated using coherent anti-Stokes Raman scattering (CARS) technique. The rovibrational level v = 1 and J = 12 of D₂ was selectively excited through stimulated Raman pumping while monitoring the temporal evolution of population for D₂(1, J ≤ 12) molecules using time-resolved CARS spectroscopy. The results demonstrate that the rotational relaxation processes of D₂(1,12) encompass both multi-quantum relaxation and continuous single-quantum relaxation. When α, the molar ratio of N₂, is less than 0.5, D₂(1,12) predominantly undergoes a single quantum relaxation process transition. However, when α ≥ 0.5, the multi-quantum relaxation mechanism gradually predominates. The total rotational relaxation rate coefficients of D₂(1,12) collisions with N₂ and D₂ at 295 K were determined to be 3.974 × 10⁻¹⁴ and 1.179 × 10⁻¹⁴ cm³ s⁻¹, respectively. The temperature dependence of rotational relaxation rate of D₂(1,12) was investigated within the temperature range of 295–453 K. With increasing temperature, the dominant relaxation process exhibited an accelerated behavior, while the minor relaxation process remained largely unaffected. The rotational temperature of the D₂ molecule at various N₂ molar ratios was determined through the utilization of Boltzmann plots. The rotational temperature undergoes a rapid decline within 2 μs, corresponding to the near-resonant rotation–vibration relaxation process of D₂(1,12) collisions with N₂. The system reaches a quasi-equilibrium state when the delay time is 3 μs. The findings of this study can serve as a valuable empirical basis for further validation of the kinetic theory and simulation. [ABSTRACT FROM AUTHOR]