Satellites of Xe transitions induced by infrared active vibrational modes of CF4 and C2F6 molecules

Abstract

Absorption and luminescence excitation spectra of Xe/CF4 mixtures were studied in the vacuum UV region at high resolution using tunable synchrotron radiation. Pressure-broadened resonance bands and bands associated with dipole-forbidden states of the Xe atom due to collision-induced breakdown of the optical selection rules are reported. The spectra display in addition numerous satellite bands corresponding to transitions to vibrationally excited states of a Xe-CF4 collisional complex. These satellites are located at energies of Xe atom transition increased by one quantum energy in the IR active v 3 vibrational mode of CF4 (v 3 = 1281 cm−1). Satellites of both resonance and dipole-forbidden transitions were observed. Satellites of low lying resonance states are spectrally broad bands closely resembling in shape their parent pressure-broadened resonance bands. In contrast, satellites of dipole-forbidden states and of high lying resonance states are spectrally narrow bands (FWHM ∼10 cm−1). The satellites of dipole-forbidden states are orders of magnitude stronger than transitions to their parent states due to collision-induced breakdown of the optical selection rules. These satellites are attributed to a coupling of dipole-forbidden and resonance states induced by the electric field of the transient CF4 (v 3 = 0 ↔ v 3 = 1) dipole. Similar satellites are present in spectra of Xe/C2F6 mixtures where these bands are induced by the IR active v 10 mode of C2F6. Transitions to vibrationally excited states of Xe-CF4(C2F6) collision pairs were also observed in two- photon LIF spectra.