The temperature dependence of the cross section for the energy pooling process Na(3P)+Na(3P)-> Na(4D)+Na(3S)

We report the measurements of the temperature dependence of the cross secti on sigma(4D) for the energy pooling process Na(3P) + Na(3P) --> Na(4D) + Na (3S). The latest two, as yet undisputed, results for sigma(4D) obtained by different authors at T = 597 K and T = 483 K suggest that this cross sectio n decreases with increasing T,which contradicts the theory and other experi ments on similar processes. To resolve this controversy and to examine the temperature trend of the cross section, we have measured the sigma(4D) in t he temperature range 567-705 K, covering the high-temperature region that h as not yet been investigated experimentally. To determine sigma(4D) we have excited sodium atoms in the quasistatic wing of the D1 line using a cw dye laser and measured the fluorescence intensity for the 4D --> 3P(3/2) trans ition, relative to the intensity of the optically thin quasistatic wing of the D2 line. The spatial distribution of the number density of the sodium a toms in the 3P(3/2) State and the sodium ground-state number density were m easured too. The method used for the determination of the cross section is advantageous since it entirely circumvents the need to account for the radi ation trapping of 3P level radiation, which was substantial under experimen tal conditions of the ground-state densities being 10(14)-10(16) cm(-3). Th e measurements of the cross section sigma(4D) in the investigated temperatu re range have shown that it increases as similar to exp(-Delta E/kT). From the experiment we obtained Delta E = (608 +/- 95) cm(-1), which is in excel lent agreement with the energy defect (613 cm(-1)) for the considered proce ss, and in fair agreement with the values which follow from recent theoreti cal calculations.