Rotation-vibration energy transfer between rovibrationally excited H₂ (v=1, J=3) and Cs₂ (X¹Σ_g⁺)

The relaxation of H₂(1,3) by collision with Cs₂ molecules has been investigated at T = 490K. Particular focus is placed on understanding both the dynamical features and the kinetics of collision which are accompanied by energy transfer into the Cs₂ vibrational and translational degrees of freedom, H₂(1,3) was prepared by stimulated Raman pumping. We have used the CARS (Coherent anti-stokes Raman Scattering) spectral technique to probe the internal state distribution of H₂ molecules. From CARS spectral peaks population rations [H₂(1,3)]/[H₂(0,3)], [H₂(1,l)]/[H₂(1,3)] are obtained. From rotational Boltzmann distribution of v = 0, these ratios indicate that [H₂(1,3)] = 7.8 × 10¹⁵cm^-3 and [H₂(1,l)] = 2.2 × 10¹⁵cm^-3. LIF (Laser induce fluoresc ence) has been used to detect collisionally excited Cs₂ (X¹∑_g⁺, v⁾. The densities of the Cs₂(X¹∑_g⁺, v⁾ were obtained by monitoring the transient absorption of the single-mode diode laser beam, turned to the B X transitions. Combining with density of the H₂(1,3), the rate coefficients for H₂(1,3)-Cs₂ (X^l∑_g⁺, v⁾ processes have been determined. For v⁼ 11, 12, 13, 14 and 15, they are (1.4±0.6) × l0^-13cm³s^-1, (1.7±0.7) × 10 -13cm³s^-1, (1.5±0.6 × 10^-13cm³s^-1, (1.3±0.5) × 10^-13cm³s^-l and (1.0±0.4) × 10^-13cm³s^-l respectively. Doppler spectroscopy was used to measure the distribution of Cs₂ recoil velocities for individual vibrational levels of the X^l∑_g⁺ state. (authors)