The electronic spectrum of pyridine in rare gas matrices

The absorption spectrum of pyridine in rare gas matrices was studied by us in the spectral region extending from 1700 Å to 2900 Å. The main results show:. (a) The 2900 Å (n → π^*) transition is similar to the corresponding gas phase transition. Only one n → π^* transition is observed. (b) In the absorption spectrum of the first π → π^* transition (¹a_1g → ¹B_2u in benzene symmetry) progressions are found with intervals of 900 cm^-1 (ν₂) starting at the origin and at a distance of 500 cm^-1 (ν₁₈), and of 300 cm^-1 from the origin. (c) Two progressions were observed for the second π → π^* transition, (¹A_1g → ¹B_1u in benzene symmetry) and intervals being 900 cm^-1 (ν₂) starting at the origin and at 500 cm^-1 (ν₁₈) from the origin. (d) One progression of 900 cm^-1 (ν₂) was observed for the thirdπ → π^* transition (¹A_1g → ¹F_1u in benzene symmetry). The spectrum represents no evidence for the splitting of the ¹E_1u state. (e) The transition to the ¹E_2g state (in benzene symmetry) was not observed.