Experimental study on rotational energy transfer in LiH (X¹ ∑ + v) + Ar collisions

Abstract

Using high-resolution transient laser spectroscopy, the rotational energy transfer between LiH (12, 8) and Ar through collisions was studied. LiH (12, 8) was generated via degenerate stimulated hyper-Raman (DSHR) scattering. The population of LiH (12, J″ ≠ 8) generated during collisions were obtained using transient laser-induced fluorescence (LIF). According to the rate equation, the rate coefficients for the transfer from (12, 8) to (12, J″) states are between 7.1×10-12 and 3.5×10-13 cm3 molecule-1 s-1 within 2 μs of the collision occurring. Above 2 μs, the rate coefficient is no longer constant. Meanwhile, no vibrational relaxation occurs before 10 μs. The rotational energy Erot is the sum of the rotational energies of rotational states (12, J″). Within the period of 0-10 μs, the value of Erot decreases from 541 cm-1 to 390 cm-1. The distribution of translational energy Etrans at different moments of LiH (12, 8) is obtained by measuring the Doppler broadened line widths. It increases from 707 cm-1 at 0 μs to 852 cm-1 at 10 μs. Therefore, when rotational relaxation occurs, the decrease in rotational energy is approximately equal to the increase in translational energy.