The determination of the vector correlation between photofragment rotational and translational motions from the analysis of Doppler-broadened spectral line profiles

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Abstract
A theoretical framework is presented to describe the possible correlation between the translational and rotational motion of a molecular photofragment, and to relate this to experimental observables. The correlation is defined by the values of a number of bipolar moments of the translational and rotational angular distributions which reflect the dynamics of the dissociation process. Detailed equations are presented for the polarization dependence of the profiles of recoil Doppler–broadened spectral lines of the photoproduct for two distinct classes of system: (i) molecular photodissociation, followed by spontaneous fluorescence by a molecular product with dispersion of its emission spectrum, and (ii) LIF excitation of a photoproduct, with or without dispersion of the resulting emission. The application of the theory is illustrated by calculating the line profiles for two model systems, each with several excitation–detection geometries. It is pointed out that there may still be detectable correlation between the product motions even for weakly predissociated parent molecule transitions in which the memory of the initial excitation is lost through extensive rotation before dissociation.