Abstract

An investigation of the IR multiphoton absorption (MPA) of ¹²CF₃I, ¹³CF₃I, CF₃Br and SF₆, excited in cell by a 10 Bars TE CO₂ laser is reported. The spatial, spectral and temporal characteristics of the laser emission versus the grating position have been carefully investigated. The main result is that the peaks observed in the different MPA spectra are undoubtedly correlated to the gain curve of the laser and not to the fine molecular spectroscopy.This result is discussed in comparison with published similar works. The most likely explanation involves a laser bandwidth effect associated with a background of weak but rather dense resonances (typical spacing of 0.1–0.2cm⁻¹). The MPA cross section of ¹³CF₃I is about half that of ¹²CF₃I pointing out the probable rôle of Fermi resonances.