Non-thermal nuclear hyperfine populations in the products of a photodissociation reaction

Coherent anti-Stokes Raman scattering (CARS) spectra of iodine atoms produc ed thermally in iodoform, CHI3, vapour and photochemically in I-2 vapour, w ith well-resolved hyperfine structure are reported. Conditions in the I-2 v apour studies were adjusted to create, effectively, either collision-free o r thermal regimes. Thermal I atom spectra compare well with predictions bas ed on the hyperfine level Raman scattering cross-sections calculated by Dru hl [Phys. Rev. A 26 (1982) 863]; a set of experimental relative Raman scatt ering cross-sections is presented. In contrast, collision-free I atom spect ra exhibit features explicable in terms of non-thermal hyperfine level popu lations in the nascent atoms. (C) 2000 Elsevier Science B.V. All rights res erved.