Complex sentence: It was originally discovered by Margaret N. Lewis and John U. White at University of California in 1939, by the observation of molecular absorption bands around 325 nm in the system designated by 2 Σ + ← 2 Π i.
Split into simpler sentences: It was originally discovered by Margaret N. Lewis and John U. White at University of California in 1939. They observed molecular absorption bands around 325 nm belonging to the system designated by 2 Σ + ← 2 Π i.