Ozone ultraviolet photolysis. VI. The ultraviolet spectrum

Abstract

The ozone ultraviolet spectrum has been re-examined at low temperature to clarify features of photochemical interest. The origin of the system is a diffuse band at 28 450 cm−1, the long wavelength limit of band structure in the cold spectrum. The bands toward higher frequencies are identified as sequences of the upper state bending (333 cm−1) and symmetrical stretching (600 cm−1) modes. This band structure converges to a limit near 32 400 cm−1, consistent with the energy required to form O(1D) plus O2(1Δ). Both the shading of the bands and sequences which appear suggest that the Huggins bands are that part of the Hartley-Huggins system which lies below the dissociation limit, the system being a single transition 1B2← X 1A1. The component of the continuum due to excitation of the ν010″ bending mode is shown to be similar to that arising from the ν000″ ground state, except for a shift toward lower energy equal to the vibrational excitation energy. A rationale for predicting the effect of temperature on the shape of the continuum is presented.

Re-analysis of the ultraviolet absorption spectrum of ozone

“…Since the first study in the 1930's, the Huggins bands of O 3 , observed between 310 and 360 nm, have been vibrationally analyzed in several different ways. Simons et al 7 agreed with the original, apparently simple, analysis 8 in which the spectrum was assigned as being made up of progressions in 1 and 2 , based on an electronic origin at 351.5 nm ͑28 450 cm Ϫ1 ͒. They also concluded that no vibrational progressions in 3 were observed.…”

“…In this paper we present a re-assignment of the vibrational structure of both the Huggins and Hartley band systems which recognizes the considerable anharmonicity that is to be expected on the weakly bound upper surface͑s͒. In these new assignments, only progressions in 1 , the symmetric stretching vibration, and 2 , the bending vibration, are observed, as in the two earliest studies, 7,8 but now all hot bands originate from one quantum of 1 in the ground state rather than from one quantum of 3 . These re-assignments produce a rather different picture of motion on the excited surface in the asymmetric stretch coordinate.…”

“…They also concluded that no vibrational progressions in 3 were observed. Brand et al 9 carried out an analysis using the data of Simons et al, 7 and based on the reported presence of 3 hot bands and a Franck-Condon analysis, deduced that the upper state has 1 A 1 symmetry, in contrast to previous theoretical calculations 10 which suggested that the Huggins bands and the Hartley continuum have the same upper state of 1 B 2 symmetry. In their vibrational assignments, 9 the position of the electronic origin remained unchanged and a long progression, up to vϭ6, in 1 was reported, while the maximum number of quanta of 2 and 3 were 1 and 2, respectively.…”

Absolute absorption cross sections of ozone in the 185‐ to 350‐nm wavelength range

“…The temperature effect is significantly larger beyond 270 nm, as can be seen in Figure 2 and Table 1. This effect is due to the changing populations of the various vibrational and rotational quantum states of the ozone molecule, and it has been analyzed in detail [e.g., Simons et al, 1973]. The crosssection values are not linearly proportional to the temperature; further more, the effect is larger at the maxima than it is at the minima of the spectral features.…”

The Huggins band of ozone: Unambiguous electronic and vibrational assignment

“…There is a one-to-one correspondence between the experimental and the theoretical assignments in Table II, which confirms the assignment of O'Keeffe et al 5 The older experimental assignments differ significantly, mainly in the number of bending and ''antisymmetric'' stretch excitations. 5,[20][21][22][23][24] In view of the limited accuracy of the electronic structure calculations, the restriction to Jϭ0 and one state, as well as the diffuseness of the measured spectrum the agreement is very good. It is similar for 18 O 3 .…”