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Identification of many Rydberg states in iodobenzene, especially from the first and fourth ionization energies (IE1 and IE4, X(2)B1 and C(2)B1), has become possible using a new ultraviolet (UV) and vacuum-ultraviolet (VUV) absorption spectrum, in the region 29 000-87 000 cm(-1) (3.60-10.79 eV), measured at room temperature with synchrotron radiation. A few Rydberg states based on IE2 (A(2)A2) were found, but those based on IE3 (B(2)B2) are undetectable. The almost complete absence of observable Rydberg states relating to IE2 and IE3 (A(2)A2 and B(2)B2, respectively) is attributed to them being coupled to the near-continuum, high-energy region of Rydberg series converging on IE1. Theoretical studies of the UV and VUV spectra used both time-dependent density functional (TDDFT) and multi-reference multi-root doubles and singles-configuration interaction methods. The theoretical adiabatic excitation energies, and their corresponding vibrational profiles, gave a satisfactory interpretation of the experimental results. The calculations indicate that the UV onset contains both 1(1)B1 and 1(1)B2 states with very low oscillator strength, while the 2(1)B1 state was found to lie under the lowest ππ(∗) 1(1)A1 state. All three of these (1)B1 and (1)B2 states are excitations into low-lying σ(∗) orbitals. The strongest VUV band near 7 eV contains two very strong ππ(∗) valence states, together with other weak contributors. The lowest Rydberg 4b16s state (3(1)B1) is very evident as a sharp multiplet near 6 eV; its position and vibrational structure are well reproduced by the TDDFT results.

The vacuum ultraviolet laser-excited photoion-pair formation spectrum of CH 3Br has been measured under high resolution in the threshold region. The (2 + 1) and (3 + 1) resonance-enhanced multiphoton ionization spectra in the same energy region are also reported. By comparison of the spectra in this and a more extended region, resonances in the photoion-pair formation spectrum are assigned to p and f Rydberg states. It is concluded that all the structure in the photoion-pair formation spectrum near threshold can be accounted for by members of the Omega = 0 subset of Rydberg states that act as doorway states to the ion channel.

A re-analysis of the Huggins and Hartley bands in the ultraviolet absorption spectrum of O 3 is presented in which the structure in both bands is assigned to vibrational progressions in the symmetric stretching mode 1 and the bending mode 2 but not the asymmetric stretching mode 3. The present improved fit of a larger range of bands results in relatively large anharmonicity terms, whereas previous assignments have relied on the motion being largely harmonic in the upper state. From a consideration of the shape of single surface required to support both sets of vibrational data, it is concluded that the Huggins bands almost certainly terminate on the 2 1 A 1 state rather than the 1 1 B 2 state.