Abstract
The spectra of the 3700-Å absorption system of SO₂, the 2491-Å absorption system of NC₂ and the 1340-Å system of SO₂ are investigated. The principal aim of this study is to find evidence for double-minimum potential functions in the excited states of these absorption systems. For the 3700-Å system of SO₂, the intensities of bands involving only symmetrical modes may be calculated accurately by application of the Franck-Condon principle. However, four non-temperature-sensitive bands of that system cannot be accounted for by the symmetrical modes. These four bands are given two alternative interpretations in terms of the antisymmetrical mode. For each interpretation, a double-minimum potential function in the Q₃ coordinate explains the positions and intensities of the bands. In the first interpretation, the interval (1⁺ - 0⁺) = 1264.0 cm⁻¹ yields a barrier height of 1700 cm while in the seconu interpretation the interval (1⁺ - 0⁺) = 416.8 cm⁻¹ gives a barrier height of 444 cm⁻¹. In the 2491-Å system of NO₂, the relative intensity of a progression of bands for which the antisymmetrical mode of vibration seems to be well established cannot be explained from a harmonic potential function. The position and relative intensity of the first band of the progression may be explained by using a three-parameter double-minimum potential function. The observed data, (1⁺ - 0⁺) = 713 cm⁻¹ and relative intensity of 1 .2 ± .2, of the first band of the progression yields a barrier height of 800 ± 150 cm. The asymmetric configuration of the molecule in the excited state, determined from the minima of the potential function, shows a departure in bond length of 7% from the average bond length determined from rotational analysis. Eight bands of the 1340-Å system of SO₂ were remeasured and the unusual isotope shifts of two of them were confirmed. Except for those isotope shifts the band system is successfully interpreted in terms of the symmetrical frequencies v₁' = 1068.5 cm⁻¹ and v₂' = 352.1 cm⁻¹. Two geometrical models of the molecule in the excited state are calculated by the FranckCondon principle and band contours are used to determine which model is correct.
Cesaní, Fernando A. (1965). A search for double-minimum potential functions in excited states of bent triatomic molecules. Doctoral dissertation, Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -174653.