ACTIVE MEDIA: Spectroscopic investigation of excimer molecules by photoabsorption and photoassociation methods. I. XeCl

The excitation spectrum of the XeCl (B, v' = 0-21) molecule was determined in a wide range of wave-lengths (315-275 nm). The molecules were formed as a result of flash photolysis by excimer laser radiation of gaseous Xe—Cl₂ mixtures of natural isotopic composition. They were then pumped by light from a frequency-tunable dye laser. A comparison of the intensities of free—bound and bound—bound transitions was used to estimate the rate constant of photoassociation, regarded as recombination of Xe and Cl atoms in which a photon acts as the third body: the rate was found to be k^{\lambda}_a approx 6×10^-29 cm⁶ s^-1 at λ approx 310.5 nm. A comparative analysis of the dependence of the intensity of the luminescence emitted by XeCl (C—A) and Xe₂Cl^*, pumped in the region of the long-wavelength absorption edge of Xe—Cl₂—Cl mixtures (λ >= 309 nm), on the pressure of xenon made it possible to identify a continuum-type absorption band with a minimum at 310.5 nm. This band was attributed to the photoassociation process XeCl(X) + Xe + hν → Xe₂Cl^* or Xe + Cl + Xe + hν → Xe₂Cl^*.