Experimental Study on the Vibrational Relaxation Mechanism of N₂(X¹Σg ⁺,v = 6) Molecules in Collision with N₂, O₂, and CO

This study employed time-resolved coherent anti-Stokes Raman scattering to investigate the vibrational relaxation mechanism of N 2 ( v = 6) molecules within the N 2 -M system, where M denotes N 2 , O 2 , or CO. At 297 K, the relaxation rate coefficients for collisions between N 2 ( v = 6) molecules and N 2 , O 2 , and CO were determined to be (2.85 ± 0.07)×10 -14 cm 3 s -1 , (6.29 ± 0.12)×10 -14 cm 3 s -1 , and (11.21 ± 0.20)×10 -14 cm 3 s -1 , respectively. The results demonstrated that the relaxation rate coefficient for N 2 ( v = 6)-CO collisions was 1.8 times higher than that for N 2 -O 2 collisions and 3.9 times greater than that for homonuclear N 2 -N 2 collisions, indicating that CO significantly enhanced the vibrational relaxation of N 2 ( v = 6). Furthermore, by analyzing the time-resolved population evolution of N 2 ( v ≤ 6) in N 2 -O 2 and N 2 -CO systems under varying buffer gas molar ratios and integrating these data with kinetic analysis, the vibrational relaxation mechanism of N 2 ( v = 6) across different collisional environments was systematically elucidated. The findings indicate that in the N 2 -O 2 system, increasing the molar ratio of acceptor molecules leads to a gradual shift from single-quantum to multi-quantum relaxation dominance. In contrast, the N 2 -CO system exhibits a transition from multi-quantum to single-quantum dominance. A systematic study examined the vibrational relaxation mechanism of N 2 ( v = 6) in two gas mixtures between 297 K and 573 K. The results indicate that elevated temperature significantly enhances the efficiency of near-resonance energy transfer associated with the dominant relaxation pathway.