Discrete and quasicontinuum level fluorescence from infrared multiphoton excited SF6

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Abstract
Infrared laser multiphoton excited SF6 shows infrared fluorescence spectra characteristic of the laser excitation process. These fluorescence experiments were conducted under dilute conditions so that the effects of collisions are essentially eliminated. After laser preparation fluorescence from molecules populating the quasicontinuum and discrete level ensembles are observed. These ensembles show distinctly different spectral characteristics which help demark energy zones which these types of levels occupy. Discrete levels which exist at lower vibrational energies show sharp fluorescence characteristic of energy localized in the laser excited mode. Quasicontinuum levels which exist at chemically interesting energies reveal that collisionless intramolecular relaxation has occured. Model calculations on thermally prepared and infrared laser prepared SF6 molecules allow the assignment of the average energy deposition into SF6 as a function of fluence, and of the population distribution of SF6 within the quasicontinuum. The model simulations of the fluorescence show that the population distribution of the quasicontinuum SF6 ensemble is nearly Boltzmann. At the lowest energies, however, a significant excess population of SF6 molecules is trapped within the discrete states.