Energy transfer kinetics of the VUV emissions for Kr–Xe mixtures

Abstract

Spectroscopic study of KrXe mixtures shows large excitation energy transfers from krypton to xenon. When small quantitities of xenon are added to krypton, these processes can be seen through the fast disappearance of the continuous krypton emissions coupled with an increase in the atomic and molecular emissions of the minority gas. The excitation transfers are very efficient since the spectra of mixtures with only a few percent Xe are very similar in shape and intensity to those of pure xenon. Kinetic analysis of all the VUV emissions enabled a complete kinetic schema of the transfer phenomena to be drawn up. They are due to binary collisions from the molecular states, Kr*2(3Σu+), which are responsible for the second krypton continuum (k2=2.107 Torr−1 s−1) and from the atomic precursor states of molecular krypton (k1=7.106 Torr−1 s−1). Both processes have large cross sections. The two paths compete in the creation of resonant Xe(3P1) states, either through direct molecule–atom transfer or by atom–atom transfer followed by infrared cascade emissions. In the mixture, the molecular Xe2* states responsible for the 173 nm continuum have a different origin to that found in the pure gas. They are created by three-body collisions Xe*(3P1)+Xe+Kr; the reaction constant is k=40±10 Torr−2 s−1.