An in-line double mass spectrometer has been employed to determine reaction rate coefficients and excitation functions for several types of negative ion reactions involving ozone. The interactions studied include electron transfer reactions, such as, M−+O3→M+O3− (where M−=O−, OH−, F−, Cl−, Br−, I−, S−, SH−, Cl−2, C2H−, NO2−, and CO3−) and particle transfer reactions, such as MO−+O2→M+O3− (where MO−=O2−, NO2−, NO3−, CO3−). Translational energy thresholds have been determined for those reactions which are endothermic by applying exact Doppler corrections for the thermal motion of the neutral as well as corrections for the translational energy distribution of the projecticle ions. These experiments place a lower limit of 2.26+0.04−0.06 eV on the electron affinity of ozone. This value is in excellent agreement with the value computed from the bond dissociation energy of O3− in its most stable configuration, D00(O−–O2) =1.80 eV, as deduced from measurements of the translational energy thresholds for the collisional dissociation process, O−3+M→O−+O2+M, where M=He, Ar. Further implications of these experiments with respect to the structure, thermochemistry, and excited states of O−3 are discussed.

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Using a Hopfield continuum source and a computer-controlled data acquisition system, we have measured relative absorption cross sections for HCl, DCl, HBr, DBr, and HI at 0.2 Å resolution from 1000 to 700 Å, a region dominated by autoionizing Rydberg states converging to the A 2Σ+ state of the HX+ ion. In order to analyze the shapes of autoionizing vibrational bands, we applied Fano’s theory of line shapes to homogeneous autoionization in diatomics, and found that the line shape parameters q, Γ, and ρ2 are independent of rotational quantum number but may depend upon the vibrational quantum number of the autoionizing state. Calculations of this vibrational dependence in HCl shows it to be most pronounced at high v. For progression I in HCl and DCl (n*=2.795) and in HBr and DBr (n*=2.748), we fit computer-generated vibronic band contours to experimental absorption cross sections to obtain q, Γ, and ρ2 which we then used to predict the photoelectron spectra of these autoionizing states. The autoionization lifetime h//Γ in HCl and DCl is 1.1×10−14 sec; in HBr and DBr it is 9.5×10−15 sec. The measured autoionization widths of bands in the next member of the Rydberg series obey the scaling rule Γ∝n*−3. We attribute an additional broadening of levels with v′?3 in progression I of HBr as the onset of predissociation, and estimate the relative rates of predissociation and autoionization. A vibrational reassignment of progression II in HCl and DCl gives n*=2.310 for these states. We saw only a single broad peak (with n*=2.78) in the absorption spectrum of HI.

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