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

Abstract

Absorption and luminescence excitation spectra of XeCF4 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 v3 vibrational mode of CF4 (v3 = 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 (v3 = 0 ↔ v3 = 1) dipole. Similar satellites are present in spectra of XeC2F6 mixtures where these bands are induced by the IR active v10 mode of C2F6. Transitions to vibrationally excited states of Xe-CF4(C2F6) collision pairs were also observed in two-photon LIF spectra. © 2011 American Institute of Physics.