PERSISTENT INFRARED HOLE-BURNING SPECTROSCOPY OF NH3D-X]2SO(4) MIXED-CRYSTALS( DOPED IN [(NH(4))X,RB1)

[(NH4)x,Rb1-x]2SO4 Mixed crystals (0.16 less-than-or-equal-to x less-t han-or-equal-to 1) were doped with NH3D+. Four of the eight N-D stretc hing bands of the NH3D+ ion gradually disappear with increasing Rb+ io n concentration while the widths of the N-D stretching bands increase, indicating that Rb+ ions first substitute NH4+ ions only in one type of crystal site, and that addition of Rb+ ions introduces glasslike di sorder into the (NH4)2SO4-type crystalline structure. Infrared hole bu rning has been demonstrated in the broadened N-D stretching band Of NH 3D+ ion using a combination of a diode laser and a Fourier-transform i nfrared spectrometer. The initial hole width decreases proportionally with the center frequency of the hole at all Rb+ ion concentrations an d agrees with the measurements of the [(NH4)x,K1-x]2SO4 mixed crystals . The similar proportionality, long known for many hydrogen-bonded sys tems in solution, suggests that the widths observed in solution are ho mogeneous. A longer irradiation time (> 10 min), however, leads to a w ider spectral hole. Measured hole decay rates decrease with decrease o f the center frequency of the hole, showing that the rotational tunnel ing barrier increases with the strength of the hydrogen bond. The chan ge of the rotational tunneling barrier with Rb+ ion concentration is a lso observed as a change of the hole decay rate (more than tenfold in the experimental range). On the other hand, the hole burning quantum e fficiency shows little change with the Rb+ ion concentration, or tempe rature. The observed steady holeburning quantum efficiency supports th e infrared hole burning mechanism proposed in our previous study: The configurational change of the hole burning must occur in the excited v ibrational state.