DYNAMICS ON THE GROUND-STATE POTENTIAL SURFACES OF H-3 AND ITS ISOTOPOMERES FROM THEIR UV SPECTRA

The uv spectra of H-3, D2H, and D-3 emitted by a neutralized ion beam have been measured in the wavelength range 200-400 nm. The spectra are continuous and show two maxima at 240 and 310 nm. Numerical simulatio ns of the uv spectra, taking ab initio potential surfaces and transiti on moments as a starting point, explain their bimodal structure as ari sing from radiative decay into the two Jahn-Teller sheets of the groun d-state potential surface. Two different lifetimes tau(1) and tau(2) f or the lower sheet and the upper sheet of the Jahn-Teller adiabatic gr ound-state surface, respectively, were introduced and varied when fitt ing the simulated spectra to the experimental ones. These lifetimes ha ve to be interpreted as average values for different vibrational state s with angular momentum quantum numbers ranging from 0 to 7. The value s are for H-3 tau(1) = 3.5 fs and tau(2) = 6.7 fs, for D2H, tau(1) = 4 .9 fs and tau(2) = 8.2 fs, and for D-3, tau(1) = 5.9 fs and tau(2) = 8 .7 fs and the error is estimated to be 0.5 fs. These results are consi stent among each other, i.e., they show the expected dependence on the square root of the reduced masses. Furthermore, lifetimes for the uv emitting Rydberg states have been measured. Since lifetimes of Rydberg states of H-3 and its isotopomeres are already known from analogous m easurements in the visible spectrum, the 3s and 3d states could be ide ntified as the main emitters of the uv radiation. Their mean lifetimes range from about 4 ns for H-3, 5 ns for H2D, and 6 ns for D2H to 10 n s for D-3. [S1050-2947(98)07208-4]