“…The emission spectra are typically highly congested, making interpretation difficult. The use of single-isotopomer sources has been the key to success in a number of cases (16,17). In addition, it has been possible to get around the ⌬⍀ ϭ 0 limitation on the multiple-resonance techniques in ICl (9,18) and Cl 2 (19), where perturbative interactions yield access to the ⍀ ϭ 2 states, and in I 2 (20), where collisional transfer does the same.…”