The 3p Rydberg states of acetone and photodissociation of the acetone cation were studied using time-of-flight(TOF)mass spectrometry.The 3p Rydberg state spectroscopy of acetone was investigated with linearly polarized two-photon resonance enhanced multiphoton ionization(REMPI)from 320 to 337 nm.Several new transition bands were observed in the spectra.In addition to the CH3COCH3 + ion,CH3CO + and CH3 + fragments were observed.The laser power dependences suggest that the CH3COCH3 +,CH3CO + and CH3 + ions are produced in three-,four-,and four-photon processes,respectively.Production of CH3CO + and CH3 + involves excitation of the ground state acetone cation by an additional photon and subsequent decomposition of the excited acetone ion.The average translational energies of CH3CO + and CH3 + from dissociation in CH3COCH3 +(X)+hv→CH3CO + +CH3 and CH3COCH3 +(X)+hv→CH3 + +CH3CO,respectively,were derived from the ion TOF peak profiles.
The intra- and inter-band relaxation dynamics of CdSe/CdS/ZnS core/shell/shell quantum dots are investigated with the aid of time-resolved nonlinear transmission spectra which are obtained using femtosecond pump-probe technique. By selectively exciting the core and shell carrier, the dynamics are studied in detail. Carrier relaxation is found faster in the conduction band of the CdS shell （about 130 fs） than that in the conduction band of the CdSe core （about 400 fs）. From the experiments it is distinctly demonstrated the existence of the defect states in the interface between the CdSe core and the CdS shell, indicating that ultrafast spectroscopy might be a suitable tool in studying interface and surface morphology properties in nanosystems.
