Molecular Energy Transfer in Highly Excited Electronic States

We present an experimental study of the energy-transfer dynamics of inert gases with lithium dimer in highly excited electronic states: \begin{eqnarray*} \mathrm{Li}_2 (3) \ \mathrm{or} \ (4) ^1 \Sigma_g^+ (v_i,j_i) + \ \mathrm{X} \ \rightarrow \mathrm{Li}_2 (3) \ \mathrm{or} \ (4) ^1 \Sigma_g^+ (v_f,j_f) + \mathrm{X}, \end{eqnarray*} with the lithium molecule prepared via two-photon excitation in a single rovibrational level in the E $(3) ^1 \Sigma_g^+$ or F $(4) ^1 \Sigma_g^+$ excited electronic states. The E state resembles the previously studied A $(1) ^1 \Sigma_u^+$ state in having nearly the same $r_e$ and $\omega_e$ values, indicating that differences in the rate constants are most likely due to difference in the spatial distributions of the electrons. We find that, in both the E and F states, rotational energy transfer occurs at a similar overall rate as in the previously studied A state. However, the distribution of final levels is dramatically different from that in the A state, being much narrower. This implies a more nearly isotropic interaction in the highly excited states. The rotational distribution of vibrationally inelastic rate constants in the F state, on the other hand, resembles that in the A state.