Theoretical study on the photoabsorption in the Herzberg I band system of the O2 molecule

Dioxygen spectra and bioactivation

“…It was shown that the b 1 Σ g + − X 3 Σ g ,1 − transition to the Ω = 1 component of the ground state is the most intense and borrows intensity from the “spin current” (spin‐flip transition between spin sublevels Ω = 1 → Ω = 0 of the ground triplet state) . Just this peculiar mechanism is responsible for the observed radiative lifetime of the b 1 Σ g + state (τ R b = 12 s) and intensity distribution in rotational structure of the A band . Radiative rate of vibronic satellites in the red atmospheric system has also found a perfect explanation on the ground of this mechanism .…”

“…Rotational branch intensities in the “Herzberg” bands and in other UV spectra in the 240–400 nm region are more uncertain . There are many attempts to fit the mechanism of their intensity borrowing to the observed intensity distribution in the rotational lines . All “Herzberg” bands are electric‐dipole allowed if SOC is taken into account, but without SOC perturbation they are spin‐forbidden (even the triplet–triplet transitions, X − A ′ and X − A ) .…”

“…Similar results (but without vibronic band calculations) have been performed on semi‐empirical MINDO/S CI level . The mechanisms of intensity borrowing for the perpendicular transitions of the Herzberg's bands are presented elsewhere . Buijsse et al have detected atomic fragments O( 3 P J ) with fine structure resolved by REMPI (2+1) techniques.…”

“…Nowadays, many rovibronic bands in the Herzberg systems are well studied in gas phase, but information about condensed phase spectra, especially on the “Herzberg III” band system is rather confusing . Even the regular spin‐orbit multiplet splitting for the A ′ 3 Δ u state has been inferred from O 2 spectra in solid deuterium in contrast with the accepted scheme in the gas phase, which seems to be rather strange.…”

Accurate ab initio potential energy curve of O2. II. Core-valence correlations, relativistic contributions, and vibration-rotation spectrum

“…It is reckoned 1-4 that the appearance of O 2 in the environment, around 2.2ϫ 10 9 years ago, had a revolutionizing effect on biochemical networks and the evolution of complex life. [8][9][10][11] The O 2 molecule manifestly plays a manifold role in the maintenance of life on earth. Since the majority of the reactions with organic molecules are with singlets, they are spin forbidden implying that they are slow at ambient conditions, a circumstance that represents a problem for living organisms wanting to employ O 2 in their metabolism.…”