An Etymological Dictionary of Astronomy and Astrophysics
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A concept used for checking the stability of a group of mass such as a → cluster of galaxies or a → star cluster. The crossing time is given by t_c = R/V, where R is the average projected radial distance of group members from the center of mass and V the Gaussian dispersion in internal velocity.

→ cross; → time.

A → radiationless relaxation process in which a molecule in some excited → electronic state converts to a state of different spin → multiplicity. Intersystem crossing is analogous to → internal conversion.

→ intersystem; → crossing.