Electric Quadrupole Transition in the A 1Π←X 1Σ+ System of CO

Abstract

In the fourth positive system, A ¹Π←X ¹Σ⁺, of CO, electric quadrupole transitions (ΔJ=2) have been observed for the first time in bands of an electric dipole allowed transition. This system also represents the first example of an electric quadrupole transition to be observed in a heteronuclear diatomic molecule. The quadrupole transition probability has been determined to be ≈1.1×10³ sec⁻¹. This value compares well with the value of ≈2.0×10³ sec⁻¹ determined for the quadrupole transition probability of the electric dipole forbidden a¹ Π_g←X ¹Σ_g⁺ transition in the isoelectronic N₂ molecule.