Orbital polarization and fine-structure effects in time-resolved cooperative fluorescence from dissociating alkali-metal diatoms

Abstract

Time-resolved cooperative fluorescence (TRCF) from electronically excited dissociating homonuclear diatoms is suggested as a new technique for studying orbital and spin-polarization effects in fragmented diatoms. The method is based on a theoretical prediction of a novel feature named here ‘superbeats’. This feature results from a combination of two oscillatory effects, namely, the ringing oscillations caused by the time variation of the interference phase between the receding atoms during emission (P. Grangier, A. Aspect and J. Vigué, Phys. Rev. Lett., 1985, 54, 418) and the quantum beats associated with the fine-structure splitting. The time-resolved superbeat pattern is shown to be sensitive to the amplitudes and phases of the superposed states, with different orbital polarization and spin, mixed by adiabatic and non-adiabatic couplings in the outcome of the dissociation process. Quantitative estimates are made, based on a detailed analysis, for the photodissociation of Li₂. Under conditions in which rotational effects can be neglected, the two states ¹Σ_u(g) and ³Π_u(g) of Li₂ are superposed in the final outcome of the reaction. This should lead to a superbeat pattern dependent on the amplitude and phase of the superposition. Conditions for the experimental observability of these features have been studied, showing that a time resolution of ≲0.1 ns is required.