Experimental study on the vibrational relaxation mechanism of N₂(${\mathrm{X}}^1{\mathrm{\Sigma }}_{\mathrm{g}}^{+}$, 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 N₂ (v = 6) molecules in N₂–M systems, where M denotes N₂, O₂, or CO. At 297 K, the relaxation rate coefficients for collisions between N₂ (v = 6) and N₂, O₂, and CO were determined to be (2.85 ± 0.07) × 10⁻¹⁴ cm³⋅s⁻¹, (6.29 ± 0.12) × 10⁻¹⁴ cm³⋅s⁻¹, and (11.21 ± 0.20) × 10⁻¹⁴ cm³⋅s⁻¹, respectively. The results demonstrated that the relaxation rate coefficient for N₂ (v = 6)–CO collisions was 1.8 times higher than that for N₂–O₂ collisions and 3.9 times greater than that for homonuclear N₂–N₂ collisions, indicating that CO significantly enhances the vibrational relaxation of N₂ (v = 6). Furthermore, by analyzing the time-resolved population evolution of N₂ (v ≤ 6) in N₂–O₂ and N₂–CO systems under varying buffer gas molar ratios and integrating these data with kinetic analysis, the vibrational relaxation mechanism of N₂ (v = 6) in different collisional environments was systematically elucidated. The findings indicate that in the N₂–O₂ system, increasing the molar ratio of acceptor molecules leads to a gradual shift from single-quantum to multi-quantum relaxation dominance, whereas the N₂–CO system exhibits a transition from multi-quantum to single-quantum dominance. In addition, a systematic study examined the vibrational relaxation mechanism of N₂ (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.