6533b874fe1ef96bd12d6390

RESEARCH PRODUCT

Molecular alignment echoes probe collision-induced rotational-speed changes

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description

International audience; We show that the decays with pressure of the rotational alignment echoes induced in N 2 O-He gas mixtures by two ultrashort laser pulses with various delays show detailed information about collision-induced changes of the rotational speed of the molecules. Measurements and classical calculations consistently demonstrate that collisions reduce the echo amplitude all the more efficiently when the echo appears late. We quantitatively explain this behavior by the filamentation of the classical rotational phase space induced by the first pulse and the narrowing of the filaments with time. The above mentioned variation of the echo decay then reflects the ability of collisions to change the molecular rotation speed by various amounts, enabling refined tests of models for the dissipation induced by intermolecular forces. We also demonstrate that the collision-induced changes of the rotational speed within the filaments are the classical equivalents of the nonsecular transfers among quantum coherences, thus evidencing the correspondence between the classical and quantum worlds.