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Infrared light on molecule-molecule and molecule-surface collisions

par Tran, Ha;Vander Auwera, Jean ;Landsheere, Xavier;Ngo, N.H.;Pangui, E.;Morales, S.B. A.;El Hamzaoui, Hicham;Capoen, Bruno;Bouazaoui, Mohamed;Boulet, Christian;Hartmann, Jean Michel
Référence Physical review. A, General physics, 92, 1-5, page (012707)
Publication Publié, 2015

Article révisé par les pairs

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Résumé :

By analyzing measured infrared absorption of pure CH4 gas under both "free" (large sample cell) and "confined" (inside the pores of a silica xerogel sample) conditions we give a demonstration that molecule-molecule and molecule-surface collisions lead to very different propensity rules for rotational-state changes. Whereas the efficiency of collisions to change the rotational state (observed through the broadening of the absorption lines) decreases with increasing rotational quantum number J for CH4-CH4 interactions, CH4-surface collisions lead to J-independent linewidths. In the former case, some (weak) collisions are inefficient whereas, in the latter case, a single collision is sufficient to remove the molecule from its initial rotational level. Furthermore, although some gas-phase collisions leave J unchanged and only modify the angular momentum orientation and/or symmetry of the level (as observed through the spectral effects of line mixing), this is not the case for the molecule-surface collisions since they always change J (in the studied J=0-14 range).