Experimental study on collision-induced rotational energy transfer between D2(1, 15) and N2.

The ro-vibrationally excited state D2(X1∑g+, v = 1, J = 15) was prepared using stimulated Raman pumping, and its collisional rotational relaxation behavior with D2 and N2 molecules was experimentally investigated at 297 K. The effective lifetime of D2(1,15) was determined by measuring time-resolved CARS signals in both pure D2 and D2-N2 systems. Combining the Stern-Volmer equation, the self-relaxation rate coefficient for D2-D2 collisions in the pure D2 system was calculated to be (2.3 ± 0.1) × 10-14 cm3 s-1. The rotational relaxation rate coefficients for D2(1,15) molecules colliding with D2 and N2 molecules in the D2-N2 system were (0.5 ± 0.1) × 10-14 and (6.0 ± 0.3) × 10-14 cm3 s-1, respectively. The results show that near-resonant rotational-vibrational (R-V) collisions between D2 and N2 accelerate the rotational relaxation of D2(1,15), which is the dominant pathway for rotational energy transfer. Time-resolved CARS spectra of D2(v = 1, J = 15, 13, 11) were recorded at 297 K under varying N2 molar ratios. Kinetic analysis revealed that R-V collisions in D2-D2 interactions primarily induce multi-quantum relaxation (J = 15 → 11). At lower N2 molar ratios, a prominent fast multi-quantum relaxation process was observed. As the N2 molar ratio increased, single-quantum relaxation via D2-N2 collisions became more dominant. The effect of temperature on the rotational relaxation of D2(1,15) was studied over the 297-400 K range. At an N2 molar ratio of 0.3, rising temperatures increased D2-D2 collision frequency, enhancing near-resonant multi-quantum relaxation. Meanwhile, secondary D2-N2 collisions prolonged the time required for single-quantum relaxation to reach its peak population. At an N2 molar ratio of 0.7, elevated temperatures significantly enhanced D2-N2 energy exchange, leading to a marked increase in D2(J = 13) population, with single-quantum relaxation becoming the dominant energy transfer pathway for D2(1,15) molecules.