Rotational time-domain CARS in H2:: departure from statistically independent collisional dephasing model

Time-domain CARS was applied to study dephasing of H-2 S-0(0) and S-0(1) rotational transitions in the density range from 0.004 to several amagat at 296 and 80 K. Dephasing of the S-0(0) transition in pure H-2 corresponds satisfactorily to the theoretical model of statistically independent collisional perturbations of translational and rotational molecular motions. Experimental dephasing curves of the S-0(1) transition in pure H-2 in the density region of the Dicke effect manifestation are steeper than the theoretical curves calculated on the basis of the statistically independent dephasing model. This departure is especially noticeable at liquid nitrogen temperature. At the same time, dephasing curves of the S-0(1) transition in He as a buffer gas measured at room temperature demonstrate fairly good coincidence with the theoretical model. The departure of the experimental dephasing curves of the S-0(1) transition in pure H-2 from the statistically independent model can be mainly attributed to resonance collisions. Copyright (C) 2003 John Wiley Sons, Ltd.