Spectroscopic data related to the structures of polyatomic molecules in the gas phase have been reviewed, critically evaluated, and compiled. All reported bond distances and angles have been classified as equilibrium (r 0)' average (r,), substitution (r.), or effective (ro) parameters, and have been given a quality rating which is a measure of the parameter uncertainty. The surveyed literature includes work from all of the areas of gas-phase spectroscopy from which precise quantitative struc• tural information can be derived. Introductory material includes definitions of the various types of parameters and a description of the evaluation procedure.

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Absorption spectra of ClO, BrO, and IO have been observed during the flash photolysis of Cl2–O2, Br2–O2, and I2–O2 mixtures. Rotational and vibrational analyses of the ClO and BrO spectra have been carried out and appropriate molecular constants derived. The transitions are of the type 2Πi(case a)—2Πi (case a). Extensive predissociation has been observed in all three spectra. Theoretical and experimental evidence is presented to show that the excited states dissociate to X(2P3/2) + O(1D). From the observed or extrapolated convergence limits of the absorption spectra the dissociation energies of the ground states are shown to be D0″(ClO) = 63.31 ± 0.03 kcal./mole, D0″ (BrO) = 55.2 ± 0.6 kcal./mole, D0″ (IO) = 42 ± 5 kcal./mole. Mechanisms for the production of the halogen monoxides are discussed and evidence is presented for the participation of excited [Formula: see text] halogen atoms.