We studied in detail the IR multiple-photon (MP) absorption in the quasicontinuum of SF6 molecule in the vicinity of the frequency of the mode ν3. The molecules were preliminarily raised to the quasicontinuum by means of a pump laser pulse, and then we measured their IR MP absorption of a probe pulse, depending on its fluence and frequency ω2, as well as on the initial excitation level (vibrational temperature) of the molecules. The latter was varied from room value to T vib = 1700 K. The frequency ω2 was varied in the range 884.18−944.2 cm-1. The IR MP absorption spectra measured, as well as the fluence and T vib dependences of MP absorption for various ω2, are intended for making a comparison with the results of the theoretical modeling of the IR MP excitation dynamics and obtaining the spectral characteristics of the IR transitions of the SF6 molecule in the quasicontinuum.

No abstract

No abstract

No abstract

The IR MP excitation spectra of the SF 6 molecule in the vibrational quasicontinuum (QC) measured experimentally in the vicinity of the ν 3 mode frequency are compared with their theoretical counterparts with a view to revealing the relative contribution from the statistical inhomogeneous broadening (SIB) and homogeneous broadening to the formation of the IR transition spectra in the QC. The IR MP spectra are found by solving rate equations, the cross sections of the successive transitions being calculated in the SIB approximation. The half-width γ L of the Lorentzian profile associated with the homogeneous broadening is the only adjustment parameter of the model. A good agreement (within the accuracy of measurement) is obtained between the experimental and theoretical IR MP spectra over a wide range of spectral and energy parameters. The γ L values are found which vary within the limits 0.53 e γ L e 10.2 cm -1 in the energy range 4500 e E e 30 000 cm -1 . The conclusion is drawn that the main parameters of the IR transition spectra in the QC (the position of the maximum, width, and intensity) are governed largely by the SIB effect, though the Lorentzian wings may play a decisive role when excitation occurs at the edges of the spectrum. The IR transition cross sections found are used to compute the IR MP excitation dynamics in the QC and determine the vibrational distribution function being formed. It is found that excitation in the QC may also give rise to a nonequilibrium bimodal distribution.