Forbidden absorption bands of O₂ in the argon continuum region

Abstract

The absorption spectrum of O2 has been photographed in the argon continuum region with a 3-m vacuum spectrograph at a dispersion of 1.42 Å/mm. Based on the known rotational constants of the ground state, the rotational constants of the upper states have been determined for Tanaka progession (I), β–X3Σg−, progression (II), α1Σu+–X3Σ−, and those of a new band at 1144.6 Å. In a brief discussion of the upper electronic states, it is suggested that both the β state and the upper states of the 1144.6 Å band are 3Σu+ states and their electron configurations are (πg2p)(3pπ) and (πg2p)(4pπ), respectively, and also the α state is (πg2p)(3pπ)1Σu+.

Rotational line strengths in 3Σ+–3Σ− electronic transitions. The β3Σu+ – X3Σg− and A3Σu+ – X3Σg− systems of molecular oxygen

“…Rotational analyses have been performed (17)(18)(19) for the (2-0) and (3-0) bands and the upper state, classified as 3Cuf by quantum defect arguments (18), is a Rydberg state converging to the X2ng ground state of 02+ (17,18). All bands exhibit varying degrees of diffuseness owing to predissociation.…”

“…The importance of 3Cf -3C-interactions in 0, has been noted also by Klotz and Peyerimhoff (20), in relation to the origin of the strength of the Herzberg I bands, and by Julienne (21) in relation to the predissociation of the Schumann-Runge B3CU--X3Cg-system. Interactions with the 1311u state may also play a part, especially at longer wavelengths, but they are expected to be secondary because of the low-transition strength (22)(23)(24) The case b rotational line strengths of Present (2) were calculated on the basis of intensity borrowing from perpendicular transitions, 311 -3E, and the same formulae follow from Table 2 and [17] and [18] if we put 2, = 0 and Yo = Y , + 0 . In this case the limiting branch strengths become ( 2 ) S:Q:O = 1:6:1 (Hund's case b, N + m ) , insufficient to explain the strong 0 -and S-form branches observed in Fig.…”

“…To test this conclusion quantitatively we performed band model fits to the measured cross section at 79 K. Using the well-known energy levels (25) for the ground state, we obtained spectroscopic constants for v' = 3 , p 3 X u f from a least-squares fit to the observed line positions of Ogawa and Yamawaki (18). In the case of 3 E f -3E-coupling, it is expected, from Table 2 , that there will be eight dominant branches in the spectrum; 'R2, , SR32, OP12, OPZ3, QR,2, QR2,, QP32, and "P,,.…”

“…Therefore, the observed lines of the S-form branch, for example, will consist of unresolved doublets. Assuming this scheme, we obtained the following constants: (18). The values of the effective spin-spin and spin-rotation constants A and IJ, are extremely approximate since.the triplet structure is not resolvable experimentally, but values for these parameters are needed to construct realistic band profiles.…”

“…We determined the Franck-Condon factor q3, = 0.172 by overlapping appropriate wave functions obtained by numerical integration of the Schriidinger equation with Rydberg-Klein-Rees potentials for the X3Cg-and p3Cu+ states. The latter potential was approximate owing to the broadness and irregularity of the experimental p3Cu+ levels (16)(17)(18)(19). The transition moment obtained by this procedure is IZ,~ = 0.045 a.u., a very large value for a forbidden transition mainly due to the relatively close proximity in energy of the p3Cu+ and B,E3Cu-states at internuclear separations near 1.2 A.…”