Rydberg, valence, and ion-pair quintet states of O2

Abstract

We report an ab initio study of the quintet states of molecular oxygen. The calculations are carried out employing the multireference single and double excitation configuration interaction package. Potential energy curves of the six quintet valence states dissociating into ground state atoms and of the four quintet states dissociating to ion-pair atoms were computed. A number of bound quintet Rydberg series converging to the a(4)Πu and b(4)Σg(-) states of the O2(+) cation have been identified.

New Aspects of the Airglow Problem and Reactivity of the Dioxygen Quintet O2(5Πg) State in the MLT Region as Predicted by DFT Calculations

“…The term energy above the ground X 3 ∑ g − state T e ( 5 Π g ) = 5.011 eV is about 0.1 eV below the dissociation limit. 35 The vibrational levels manifold of the O 2 (1 5 Π g ) state had been earlier identified by the resonance-enhanced multiphoton ionization (REMPI) experiments 27 where collision transfer to the quintet state was induced from the highly excited rovibronic O 2 (A, A′, c) Herzberg states; 17 this was the first demonstration that the quintet state is produced via reaction 3. The REMPI method provides an ion signal, being a function of wavelength from ionization laser following excitation in the Herzberg I vibronic band O 2 (A 3 ∑ u + ← X 3 ∑ g − ) absorption to v = 9 level.…”

“…There are 5 more valence quintet states besides the O 2 ( 5 Π g ) quintet which correlate with the ground state oxygen atoms dissociation limit according to the Wigner-Witmer rules. 35 These are 5 Δ g , 5 ∑ u − , 5 Π u , and two 5 ∑ g + states. All of them have very shallow minima with dissociation energy less than 0.01 eV and long internuclear distances about 3.5−4 Å.…”

“…32 From experimental spectroscopic and theoretical arguments there is a reason to believe that its dissociation energy (D e ) is in the range 1000 ± 100 cm −117 and the 5 Π g zero level (v = 0) lies close or slightly above the A 3 ∑ u,1 + (v = 8) vibrational level. 17,35 Figure 1 provides a comparison between PECs of the 1 5 Π g and A 3 ∑ u + states calculated by Partridge et al with the multireference configuration interaction (MRCI) method and Davidon correction. 32 The most recent ab initio calculations 34,35 predict the equilibrium distance about 2.2 Å and D e = 713 cm −1 with 11 vibrational levels inside the well.…”

“…33−35 Many Rydberg quintet states were observed as progressions converging to various O 2 + limits. 35 Very stable valence quintet states with broad minima dissociating to the ion-pair O + ( 4 S 3/2 ) + O − ( 2 P 1/2 ) limit at 17.3 eV are predicted and partly identified by Lefebvre-Brion et al 35 According to their results, generalized in Figure 2, the ion-pair limit is difficult to reproduce, since it is achieved at very long interatomic distance (Coulomb attraction of O + and O − ions is really long ranged). This is important for our purposes that among this quintet family there is the second 2 5 Π g state with the term energy T e = 11.75 eV and equilibrium distance r e = 2.44 Å (4.61 a 0 ).…”

“…This is important for our purposes that among this quintet family there is the second 2 5 Π g state with the term energy T e = 11.75 eV and equilibrium distance r e = 2.44 Å (4.61 a 0 ). 35 The 0−0 transition 1 5 Π g → 2 5 Π g needs the excitation energy 6.74 eV in UV region (184 nm) and is forbidden in electric dipole approximation for one-photon absorption. But it is allowed and easy achieved as the multiphoton transition.…”