Rotational Structure of Some Electronic Bands of Chlorine Dioxide

The rotational structure of several violet absorption bands of ClO2 has been studied. The bands considered correspond to the vibration transitions (v1′ 0 0)←(0 0 0) where v1′ = 1, 2, 3, 4, and 5. The most prominent identifiable feature of the rotational structure is a doublet qQ branch resolved in the tail of each band. For v1′ = 1, 2, and 3, the rotational wave numbers of these branches are given by ν1,2r=−12(0.0615+0.0042v1′)L(L+1) −12(1.188+0.008v1′)K2+0.13L+0.174(v1′−0.4)K ∓12[0.109(2K−L)−0.045(v1′−1)].This fits the spectrum in the observed range of quantum numbers, K = 11 to 20 and L = K to K+8. The first two terms are associated with that prolate symmetrical top which comes closest to the actual ClO2 molecule. Hence, neglecting the effect of asymmetry on the spectrum, 2ΔB̄=−(0.0615+0.0042v1′) cm−1and 2(ΔA−ΔB̄)=−(1.188+0.008v1′) cm−1.The last term is associated with spin doubling. The coupling is shown to be close to Hund's ``case b.'' The linear terms in L and K may be a consequence of the doubling. The term in v1′K describes an outstanding feature of the spectrum but is not interpreted. The bands are shown to be of the parallel type. A few qP and qR branches have also been identified and Δ1F values have been found. Assuming the spectrum to be that of a prolate symmetrical top, the resulting values of 2B̄ for the vibrationless states are 2B̄″ = 0.612 cm−1 and 2B̄′ = 0.550 cm−1. The value of 2B̄″ with the Cl–O distance s″ = 1.53A from electron diffraction is sufficient to determine the lower electronic state. The upper state is then determined from the values of 2ΔB̄ and 2(ΔA — ΔB̄) for the vibrationless states. The resulting model of both states is designated as model (2). Error in this model, because of the fact that the effect of asymmetry was neglected, is found to be small. Asymmetry correction made on model (2) leads to the following model: 2θ′′=109∘±3∘,2θ′=92∘±6∘, s′′=1.53A±0.02A, s′=1.805A±0.05A.The rotational isotope effect is observed and explained but gives no additional information about the molecular model.