Photoelectron spectroscopy of heterocycles. Azaindenes and azaindolizines

The HeI photoelectron (PE) spectra of indole (1), benzimidazole (2), indazole (3), 3‐chloro‐indazole (4), imidazo[1,2‐b]pyridazine (5), 6‐chloroimidazo[1,2‐b]pyridazine (6), 2‐phenyl‐imidazo[1,2‐b]pyridazine (7), 2‐phenyl‐6‐chloroimidazo[1,2‐b]pyridazine (8), tetrazolo[1,2‐a]‐pyridine (9) and 8‐cyanotetrazolo[1,5‐a]pyridine (10) have been recorded. The spectra of 2–10 are of special interest for studying lone pair interactions. The assignment of the PE spectra submitted here, conjointly with the electronic structure of the studied compounds is discussed on the basis of molecular orbital calculations.