MICROWAVE SPECTRA OF THE $HD^{+}$ AND $D_{2}^{+}$ IONS AT THEIR DISSOCIATION LIMITS.

$^{1}$ A. Carrington, I.R. McNab and C.A. Montgomerie, Mol. Phys., 65, 751 (1988). $^{2}$ A. Carrington, I.R. McNab and C.A. Montgomerie, Phys. Rev. Lett. 61, 1573 (1988).Author Institution: Department of Chemistry, Southampton University; Physical Chemistry Laboratories, South Parks Road, Oxford, UKWe have observed microwave transitions in the $HD^{+}$ and $D_{2}^{+}$ ions involving energy levels very close to their dissociation limits. In $HD^{+}$ the spectrum detected arises from a rotational transition between the two highest bound vibration-rotation levels in the 1s6 ground state (v--21 and $v-22)^{1}. D_{2}^{+}$ has seven vibration-rotation levels supported by the van der waals minimum in the first excited $2p \sigma_{u}$ electronic $state^{2}$ and we have detected microwave electronic transitions between these and high-lying vibration-rotation levels of the ground $1s\sigma_{g}$ electronic state