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.
Temporally and spatially resolved investigations of the efflorescence of equimolar mixtures of ammonium sulfate (AS) and ammonium nitrate (AN) aerosol droplets were performed by confocal Raman spectroscopy combined with high-speed photography. Information was obtained on the dynamic process of morphological changes and the heterogeneous distribution of efflorescence products. The supersaturated AS/AN mixed droplet was found to first precipitate as the double salt 3AN·AS when the relative humidity was 50%. The excess AS was irregularly distributed on the surface of the double salt as an inclusion structure. No formation of 2AN·AS was observed throughout the efflorescence process.
Resonance-enhanced multiphoton ionization of the titanium atoms has been investigated in the 293 321 nm wavelength. We couple a laser-ablated metal target into a molecular beam to produce free atoms. Ions produced from photoionization of the neutral atoms are monitored by a home-built time-of-flight mass spectrometer. Photoionization cross sections of the excited states of Ti I were deduced from the dependence of the ion signal intensity on the laser intensity for photon energies close to the ionization threshold. The values obtained range from 0.2 Mb to 6.0 Mb. No significant isotope-dependence was found from measurements of the photoionization cross sections of ^46Ti, ^47Ti, and ^48Ti.
The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ～ 1.6 ps with exciting at 400 nm,depending on the state of the photo-excited hole.The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots.In addition,Auger relaxation of trapped carriers is observed to occur with a time constant of ～ 5 ps.A schematic model of photodynamics is established based on the results of the spectroscopy studies.Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.
