Collisional Energy Transfer Between LiH Molecules And Excited H₂ Molecules

Collisional energy transfer between excited molecules and ground state molecules is an important way for studying chemical reaction kinetics and continues to be an frontier and hot research subject of atomic and molecular collisions. In this work, we have investigated collisional energy transfer between the excited vibrational states of H₂ and the ground state LiH molecules by stimulated Raman pumping?high resolution transient laser induced fluorescence?LIF? spectroscopy and coherent anti stokes Raman scattering ?CARS? spectroscopy techniques.The excited vibrational states of H₂ ?1,3? and H₂ ?1,1? are populated by stimulated Raman pumping, and the excited H₂ molecules collision with the ground state LiH molecules. The rotational states of LiH were measured by high resolution transient laser induced fluorescence ?LIF? spectroscopy. Based on the Doppler profiles of the rotational lines, we have obtained the result that the translational energy of LiH increased 50% when H₂ energy increased 13%. The rotational states distribution of LiH is a double exponential distribution which is produced by weak and strong collision, respectively. The rotational states distribution of LiH produced by weak and strong collision is sensitive to H₂ energy while the branching ratio of weak and strong collision is nearly unchanged for different H₂ energy.The molecular density of H₂?1,3? and H₂?1,1?can be obtained through measuring the CARS relative intensity of Q?1??Q?3? branch of H₂ 2-1 vibration band. The LIF intensity ratio before and after impact for LiH rotational states were measured by high resolution transient laser induced fluorescence ?LIF? spectroscopy. Based on the rate equations analysis, the appearance rate coefficients of LiH?0, J? rotational states and the average depletion rate coefficients of low rotational states are obtained.The sum of appearance rate coefficients of LiH?0,J=0-13?are kapp=?3.6±0.9?×10-11cm3molecule-1s-1 and kapp=?3.4±0.9?×10-11cm3 molecule-1s-1 for H₂ ?1,3?+LiH and the H₂?1,1?+LiH collisions, respectively. The average depletion rate coefficients of LiH?0,J=0-7? are kdep=?3.2±0.8?×10-11cm3molecule-1s-1 and kdep=?3.6±0.9?×10-11cm3molecule-1s-1 for H₂?1,3?+LiH and the H₂?1,1?+LiH collisions, respectively. The calculation results show that collisional transfer rate coefficients are basically independent of H₂ energy in vibration-rotation and translation ?V-RT? energy transfer.