Diffusion effects on relaxation measurements. Example: vibrational relaxation of NO (v=5) molecules studied by laser-induced fluorescence

Abstract

Using time-resolved laser-induced fluorescence the authors have studied the relaxation of vibrationally excited nitric oxide molecules. For the higher pressures (7 and 10 Torr) the experimental results are in fair agreement with the predictions from the V-V and V-T rate of constants determined by Horiguchi and Tsuchiya (1971). For lower pressures (0.5 to 5 Torr) the diffusion of the species has to be taken into account. The authors have studied this diffusion effect on the basis of the following hypothesis: initial radial distribution of the excited molecules of a Gaussian-type; no boundary conditions, since the cell radius is much greater than the radial extension at any time considered. With this model they were able to explain the low-pressure results.