Collisional Energy Transfer between Highly Vibrationally Excited CsH(X¹Σ⁺, v=15–22) and H₂

The Cs atoms are prepared in the 6D state by two−photon absorption. CsH(X¹ Σ⁺,v"=0) is generated from the Cs(6D)+H₂ reaction. By overtone excitation with a pulsed dye laser, highly vibrational states v"≥15 of CsH in its ground electronic state are obtained. A diode laser is used to probe either the prepared vibrational state or the collisionally populated states. The decay signal of the time−resolved fluorescence from the A¹ Σ⁺(v')→X¹ Σ⁺(v") transition is monitored. Based on the Stern–Volmer equation, the total rate coefficients for v"=15–22 are yielded. The time evolution and relative intensities of three related states, v", v"−1 and v"−2, made by the initially prepared v" state of CsH are measured. Rate coefficients of single− and double-quantum relaxation are obtained. These results show that single-quantum relaxation accounts for ≥50% of the total relaxation out of states v"=17–20. Multiquantum relaxation (Δv≥2) makes major contribution (≥62%) to the vibrational relaxation at v"=21 and 22. A simple explanation is given.