A. Durand et al., HYPERFINE STRUCTURES OF PENDULAR STATES I N ICL A-STATE AND X-STATE, Comptes rendus de l'Academie des sciences. Serie II. Mecanique, physique, chimie, astronomie, 319(7), 1994, pp. 739-744
When a polar molecule is in an intense electric field, the first rotat
ional levels are trapped by the dipole field interaction and become pe
ndular. We present here the first results of an experimental and theor
etical study of the hyperfine structures of these states in the case o
f ICl A - X transition. We show that the hyperfine structure is the ke
y for an unambiguous assignment of the observed lines. We thus prove t
hat the dipole moments of the A and X states have the same sign, a res
ult in contradiction with previous works but in good agreement with si
mple quantum chemistry arguments.