FORBIDDEN TRANSITIONS IN DIATOMIC MOLECULES: II. THE ABSORPTION BANDS OF THE OXYGEN MOLECULE

Abstract

The forbidden [Formula: see text] absorption bands of O2 in the near ultraviolet have been obtained under high resolution with absorbing paths up to 800 m. A detailed fine structure analysis has been carried out. It confirms the identification of the band system as a [Formula: see text] transition. Precise values of the rotational constants Bν and Dν as well as of the vibrational quanta [Formula: see text] in the upper state have been derived. Each of the "lines" of the Q branches observed under low dispersion is resolved into six components whose spacing yields the triplet splitting in the upper state. This splitting is more than twice as large as in the [Formula: see text] ground state and is of opposite sign. The splitting constants λ and γ have been determined and their variation with the vibrational quantum number observed. In addition to the Q-form branches weak O- and S-form branches have been found in agreement with the prediction of Present which is based on the assumption that spin–orbit coupling is the main cause for the occurrence of this forbidden transition. However, the relative intensities of the different branches deviate strongly from Present's prediction. The dissociation limit obtained from the convergence limit of the bands (without extrapolation) is at 41219 ± 40 cm.−1 This value is higher by about 220 cm.−1 than the value of the dissociation energy of O2 derived from the Schumann–Runge bands. It is possible that the limit of the Schumann–Runge bands, which is based on a short extrapolation, and therefore the value of the dissociation energy of O2 has to be slightly revised. The electron configurations and dissociation products of the various electronic states of O2 are briefly discussed.