CONTROL OF TIME-DEPENDENT NONADIABATIC PROCESSES 
BY AN OSCILLATORY EXTERNAL FIELD

Yoshiaki Teranishi $^{a}$ and Hiroki Nakamura$^{a,b}$ 
$^a$ The Graduate University for Advanced Studies, Okazaki 444, Japan
$^b$ Institute for Molecular Science, Okazaki 444, Japan

A new idea of controlling nonadiabatic transitions by an external field
is proposed. The basic principle is to periodically sweep an external
field at each level crossing to make the overall transition probability
from an initial state to any desirable final state equal to unity. The
recently completed semiclassical theory of nonadiabatic transition
enable us to analytically deal with this problem. The　present idea may
be applicable to various physical and chemical problems, whenever level
crossings are created by an external field.