Time-dependent pump-probe spectra of NeBr_2

摘要

Time-and frequency-resolved pump-probe measurements on NeBr_2 have been performed to better characterize its fragmentation dynamics on the B electronic state for vibrational levels in the energy region of the transition from direct vibrational predissociation to intramolecular vibrational relaxation dynamics.Above nu' = 20 of the Br_2 stretching mode,it was observed that the dependence of lifetime on the vibrational quantum number deviates from the energy-gap law by leveling off in the range of 10 ps< tau<20 ps.In addition to measuring the appearance of Br_2 product state levels,we were able to monitor the decay of the initially excited NeBr_2 via B->E transitions of the complex.These transitions are shifted 20 cm~(-1)to lower energy from the free Br_2 resonances,indicating an E state Ne-Br_2 bond energy of 82cm~(-1).Measurements of NeBr_2 vibrational predissociation via the DELTA nu=-2 channel were also performed for nu'' =21,28,and 29.The closing of the DELTA nu-l channel leads to an increase in the lifetimes of these vibrational levels.A new Nd:yttrium aluminum garnet pumped dual optical parametric oscillator/optical parametric amplifier system is described that allows us to conveniently record time-delayed pump-probe spectra with 2-cm~(-1)spectral resolution and 15-ps time resolution.