In this paper a coherent superposition of angular momentum states created by
absorption of polarized light by molecules is analyzed. Attention is paid to
the time evolution of wave packets representing spatial orientation of
internuclear axis of diatomic molecule. Two examples are considered in detail.
Molecules absorbing light in a permanent magnetic field experiencing Zeeman
effect and molecules absorbing light in a permanent electric field experiencing
quadratic Stark effect. In a magnetic field we have a wave packet that evolves
in time exactly as classical dipole oscillator in a permanent magnetic field.
In the second case we have the wave packet that goes through periodical changes
of a shape of the packet and revivals of initial shape. This is a pure quantum
behavior. Classical motion of angular momentum in an electric field in case of
quadratic Stark effect is known to be aperiodic. Obtained solutions for wave
packet evolution are briefly compared with Rydberg state coherent wave packets
and harmonic oscillator wave packets.Comment: LaTeX, 3 figure
