New magnetic dipole transition of the oxygen molecule: Bʹ³Πg←X ³Σg⁻(0,0)

Abstract

Through the use of isotopically pure gas at a temperature of 77 K, a weak photoabsorption band of ¹⁶O₂ is found near 1856 Å, underlying the stronger Schumann–Runge (SR) band B³Σ−u←X³Σ−g(8,0). The location, structure, and intensity of this new band are consistent with expectation for the magnetic dipole transitionB′ ³Πg←X³Σ−g(0,0), where the designation B′ is chosen to represent the II ³Πg valence state. This electronic transition contributes to the “excess absorption” underlying the SR bands [B. R. Lewis, S. T. Gibson, and E. H. Roberts, J. Chem. Phys. 115, 245 (2001)].