Isotope effects in the multiphonon relaxation of hydrated and deuterated cesium chloromanganate (CsMnCl/sub 3/x2H/sub 2/O,x2D/sub 2/O)

The electronic transition between the /sup 4/T/sub 1/ and /sup 6/A/sub 1/ states of the Mn/sup 2 +/ ion in CsMnCl/sub 3/x2H/sub 2/O has been observed to be weak compared to the same transition in other hosts, due to vibrational quenching. We have observed fluorescence and infrared-absorption spectra of the deuterated compound CsMnCl/sub 3/x2D/sub 2/O and report little change in the phonon sideband associated with the pure electronic transition, but observe a 15-fold increase in the lifetime of the excited state, along with an increase in the /sup 4/T/sub 1/ luminescence intensity. Infrared spectra reveal an intense band of high-frequency phonons which exhibits a large shift in energy with isotopic substitution. We show that these data are consistent with the theory of multiphonon transitions recently presented by Huang and Gu.