The vacuum ultraviolet laser-excited photoion-pair formation spectrum of CH3Br 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 Ω = 0 subset of Rydberg states that act as doorway states to the ion channel.

The optical–optical double resonance spectra of I2 and I2–Xe mixtures at room temperature reported in the literature using a fixed-wavelength, broad band pump laser have now been recorded using a tuneable, narrow band source. We show that during the time of the overlapped laser pulses (∼10 ns) and with 10–20 Torr of Xe there is widespread collisional energy transfer in the intermediate state and that this phenomenon offers an alternative explanation for the broad bands in the excitation spectrum, assigned to XeI2 complexes by the authors of the earlier study (M. E. Akopyan, I. Y. Novikova, S. A. Poretsky and A. M. Pravilov, Chem. Phys., 2005, 310, 287). Dispersed emission bands, previously attributed to direct fluorescence from the ion-pair state(s) of the complexes, are re-assigned to emission from ion-pair states of the parent I2 that are populated by collisional energy transfer out of the initially excited state.

A range of vibrational levels of the D 0u+(3P2) and F′ 0u+(1D2) ion-pair states of I2 is shown to be easily generated by amplified spontaneous emission (ASE) from their more accessible partners, E 0g+(3P2) and f′ 0g+(1D2), in sufficient concentration for dispersed fluorescence studies of the D 0u+(3P2) → 0g+(bb) and F′ 0u+(1D2) → 0g+(bb) transitions to be carried out. T0 (J = 49) of this shallow-bound 0g+(bb) valence state is unambiguously determined and an improved Re value of 3.952 ± 0.005 Å is obtained from optimizing the fit of the intensities of the vibrational progressions in the 0g+(bb) state, and Te is found to be 27311.3 ± 2 cm−1, leading to De = 442.0 ± 2 cm−1.

Indirect evidence for amplified spontaneous emission (ASE) between two pairs of ion-pair states of I2, namely E0g+(3P2)/D0u+(3P2) and γ1u(3P2)/β1g(3P2) has been obtained. Direct E0g+(3P2)→B0u+ and β1g(3P2) → A1u ASE has also been observed based on the narrowed time profile of the fluorescence, the latter as a secondary process following γ1u(3P2) → β1g(3P2) ASE.The 180°, amplified spontaneous emission, time profile of the β1g(3P2) → A1u emission is narrower than that of the 90°, conventional fluorescence.

A combination of (i) two- and three-photon resonance enhanced multiphoton ionization techniques with linear and circular polarization, (ii) a comparison with the single-photon absorption spectrum and (iii) isotopic substitution has been used to study the Rydberg states of furan (C4H4O). The three X[2A2]c;3p states have been unambiguously assigned from the identification of the promoting modes involved in the strong false origins observed in the two-photon spectrum. The frequencies of the A1 vibrational modes of the ion-core that are Franck–Condon active are reported. The l values of the higher Rydberg states are assigned from their quantum defects and a comparison of the single-, two- and three-photon spectra, up to the ionization limit, reveals a strong propensity for excitation of d series with two photons and p and f series with one and three photons.

A range of vibrational levels of the D 0u+(3P2) and F′ 0u+(1D2) ion-pair states of I2 is shown to be easily generated by amplified spontaneous emission (ASE) from their more accessible partners, E 0g+(3P2) and f′ 0g+(1D2), in sufficient concentration for dispersed fluorescence studies of the D 0u+(3P2) → 0g+(bb) and F′ 0u+(1D2) → 0g+(bb) transitions to be carried out. T0 (J = 49) of this shallow-bound 0g+(bb) valence state is unambiguously determined and an improved Re value of 3.952 ± 0.005 Å is obtained from optimizing the fit of the intensities of the vibrational progressions in the 0g+(bb) state, and Te is found to be 27311.3 ± 2 cm−1, leading to De = 442.0 ± 2 cm−1.

The optical–optical double resonance spectra of I2 and I2–Xe mixtures at room temperature reported in the literature using a fixed-wavelength, broad band pump laser have now been recorded using a tuneable, narrow band source. We show that during the time of the overlapped laser pulses (∼10 ns) and with 10–20 Torr of Xe there is widespread collisional energy transfer in the intermediate state and that this phenomenon offers an alternative explanation for the broad bands in the excitation spectrum, assigned to XeI2 complexes by the authors of the earlier study (M. E. Akopyan, I. Y. Novikova, S. A. Poretsky and A. M. Pravilov, Chem. Phys., 2005, 310, 287). Dispersed emission bands, previously attributed to direct fluorescence from the ion-pair state(s) of the complexes, are re-assigned to emission from ion-pair states of the parent I2 that are populated by collisional energy transfer out of the initially excited state.