Direct measurement of the fine-structure interval of Al-27 in its ground P-2 state

The J=3/2<--1/2 fine-structure transition in atomic Al-27 in its ground P-2 state has been detected in the laboratory by far-infrared laser magnetic r esonance. The fine-structure interval has been measured accurately as 3359. 6228(17) GHz or 112.064 95(6) cm(-1). The spectra show the hyperfine struct ure associated with a nuclear spin of 5/2 for Al-27. The splittings are wel l reproduced by the hyperfine parameters determined earlier by atomic beam methods. The analysis of the laser magnetic-resonance spectra casts doubt o n the published value for the Zeeman parameter g(3/2) also from the atomic beam measurements. Although the value determined in this paper is intrinsic ally much less accurate, it is in better agreement with the value obtained by a completely independent theoretical calculation. [S1050-2947(99)10307-X ].