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Summary: 491
Tutorial/Article didactique
The evolution and revival structure
of angular momentum quantum wave
packets
Marcis Auzinsh
Abstract: 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 the spatial orientation of the internuclear axis of a diatomic
molecule. Two examples are considered in detail. Molecules absorbing light in a permanent
magnetic field experiencing the Zeeman effect and molecules absorbing light in a permanent
electric field experiencing the quadratic Stark effect. In a magnetic field, we have a wave
packet that evolves in time exactly as a classical dipole oscillator in a permanent magnetic field
(classical-physics picture of the Zeeman effect). In the second case, we have a wave packet
that goes through periodical changes of shape of the packet with revivals of the initial shape.
This is pure quantum behavior. The classical motion of angular momentum in an electric field
in the case of a quadratic Stark effect is known to be aperiodic. Solutions obtained for wave
packet evolution are briefly compared with Rydberg-state coherent wave packets and harmonic-
oscillator wave packets. Zeeman and Stark effects in small molecules continuously attract the
attention of researchers, theoreticians, as well as experimentalists. These investigations allow
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