 
Summary: Separation of quadratic and linear external field effects
in high J quantum beats
M. Auzinshand R. Ferber
Department of Physics, University of Latvia, 19 Rainis Blvd, Riga LV1586, Latvia
A. V. Stolyarov
Department of Chemistry, Moscow M. Lomonosov State University Moscow, 119899, Russia
(Received 21 March 1994; accepted 22 June 1994)
We discuss quantum beats in electronically excited molecular states with high rotational angular
momenta J appearing in time resolved fluorescence in conditions of quadratic and linear energy shift
dependence on magnetic quantum number M and external field strength. Density matrix formalism
is used to obtain in explicit form the expressions for time dependent fluorescence intensity after
&function pulsed excitation. In case of pure quadratic Stark effect, which is typical for `2 state
diatomics, excited state quantum beats for .B 1 exhibit a regular, or "grill" structure, consisting of
narrow equidistant "principal" peaks with equal relative amplitudes on the exponential decay
background. At linear polarized excitation the time intervals between the adjacent peaks are 27r/ozu,
wzObeing the splitting frequency between coherently excited Msublevels with M = 2 and M' = 0.
If an admixture of linear contribution is present in field induced level shifts, the grill structure is
superimposed by a single frequency harmonic modulation. A special geometry was found in which
the quadratic beats are fully absent and the modulated grill pattern is brought into existence only by
the influence of linear term. Such a case takes place when the light polarization vector in
