Based on the quantum Liouville formalism, a theory of the two-color, triply resonant four-wave mixing is developed for molecules with isotropically oriented angular momenta. The approach allows to
strictly incorporate the relaxation matrices
(r)(r=0, 1, 2) into the third-order susceptibility
χ(3) whose expression acquires therewith the form of a scalar product in the line space. Thanks to this
representation, isolation of all resonance terms from χ(3) becomes a routine task. Some of these terms correspond to the case when a molecule initially interacts with two pump photons of the same frequency. Such interactions give rise to the grating line-space vectors which have the same (zero) eigenfrequency. Due to this degeneracy, the latter are easily mixed by rotationally inelastic collisions which
shows up in a state-resolved coherence transfer. The satellite signals induced thereby provide a great
scope to study the state-to-state inelastic ratesin situby purely optical means. If the diagonal form of
is assumed,