The optical absorption spectra of H2O and D2O are reported at various pressures for 2000?λ?950 Å. The 1670 Å band is vibrationally structured (ν2 bend) and the excited 1B1 state contains a considerable intravalence 4a1 component. The 1280 Å state 3sa1; 1A1 is linear and dominantly Rydberg. A Renner–Teller analysis of the 1280 Å band leads to detection of a perturbing state at 1365 Å which may be assigned as a bent, heavily Rydberg 3sa1; 1B1 state. A reanalysis of K-shell excitation spectra bolsters this 3sa1; 1B1 assignment. Isotope shift studies in the 1130–980 Å region lead to some vibronic reassignments. The terminal state of the 968 Å absorption band is a linear 5sa1; 1A1 state. In sum, a total of 21 electronic states, comprising fragments of six Rydberg series, have been assigned.

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The absorption spectra of high-n Rydberg states of methyl iodide and benzene perturbed by varying number densities of hydrogen or argon, range 0.9×1020–10.5×1020 cm−3 for H2 and 0.6×1020–7.5×1020 cm−3 for Ar, have been investigated. The high-n molecular states of both absorbers were found to shift linearly with the number density of atomic Ar and molecular H2 scatterers. The Fermi formula modified by the Alekseev–Sobel’man polarization term provides an excellent fit of the shift data. The electron scattering lengths obtained are: 0.93 a0 for H2 and −1.63 a0 for Ar using the CH3I absorber; and 0.99 a0 for H2 and −1.57 a0 for Ar using the C6H6 absorber. The electron scattering lengths for H2 and Ar agree with the results of an empirical model that correlates scattering lengths and the polarizabilities α(spherical) for inert atoms and α2(nonspherical) for H2 molecule.

A doubling of absorption bands occurs in certain transitions associated with first s- and p-Ryderg excitations in C2H5Br and C3H7Br. No such doubling occurs in the first d-Rydberg or second s-Rydberg excitation of C2H5Br. Furthermore, doubling is not evident in any Rydberg transition of CH3Br, CD3Br, or C2D5Br. The interpretation of this doubling phenomenon invokes vibronic coupling between Rydberg states of the same configuration. The active vibration is a C–H stretching mode ??3000 cm−1 and the presence of doubling is determined by coincidence (or near coincidence) of the intraconfigurational splitting and the frequency of the active vibrational mode.