Long-lived metastable anions of hydrogen halides

We search for narrow resonances in cross-sections for electron collisions with HCl, DCl, HBr and DBr molecules, calculated with the nonlocal resonance model. Narrow resonances corresponding to long-lived metastable states of anionic molecules are indeed found in both elastic and vibrational excitation cross-sections. The largest lifetime τ = 0.11 ms is predicted for HBr⁻ with rotational quantum number J = 20. For HCl we find maximum τ = 0.6 ns for J = 22 and τ = 0.6 μs for J = 33 in DCl. A surprising isotope effect is found for DBr, where the largest lifetime is τ = 1.5μs, i.e., much smaller than for HBr.