Investigations On Radiative Parameters Of V Ⅰ, Sn Ⅰ And Mo Ⅰ And Ⅱ Levels

Radiative parameters such as radiative lifetimes, transition probabilities andoscillator strengths of atom and ion are important and basic data in the investigationsof plasma physics, atomic physics and astrophysics. Especially in astrophysics,oscillator strengths obtained by combining radiative lifetimes and branching fractionscan be used to determine the abundance of elements of the celestial body. Whilethrough the analysis for the abundance of elements, the nuclear synthesis and theorigin and evolution of celestial bodies could be learned. Hence, the experimentalmeasurements of radiative lifetimes and branching fractions of atom and ion are ofgreat significance.Due to the very rich abundance of the elements of iron group and the fifth periodin the hot stars and CP stars, radiative lifetimes and branching fractions of V I, Sn Iand Mo I and II levels were measured and calculated in theory, and the correspondingtransition probabilities and oscillator strengths were obtained.The laser-induced fluorescence spectroscopy technique was used for lifetimemeasurements, and the details were as follow: a532nm pulse emitted from aNd:YAG laser was focused through a lens on an interested metal foil which was23mm thick and in a vacuum chamber to produce plasma. Then, another532nm pulsefrom Nd:YAG laser was used to pump a dye laser in which a DCM dye was operated.The second or third harmonics of the output was used to excite the atom or ion in theplasma to the studied levels. Fluorescence emitted from the excitation level wascollected and focused into the monochrometer for dispersion, and then was detectedby a photomultiplier and transited to an oscilloscope. The collisional effect, saturationeffect and flight-out-of-view effect which can probably influence the results in themeasurements were checked and eliminated by changing the slits of monochrometer, adjusting the intensities of ablation and excitation light and the delay time betweenthe ablation pulse and excitation pulse. The lifetime was obtained by fitting therecorded fluorescent curve: a pure exponent function fit was adopted for the lifetimelonger than60ns, and a deconvolution was used for others.During the measurements of branching fractions, the emission fluorescence ofhollow cathode lamps interested was dispersed by a grating monochrometer, and thenwas detected by a photomultiplier. The signal was A/D converted by NCL and thentransited to a personal computer for analyzing and recording with a SpectraSensesoftware. The signal curve obtained was Gaussian profile and was performedGaussian fit with Origin7.5. The peak height was adopted as the measured intensityof the line. The real intensity was obtained by correcting with the response value ofthe corresponding wavelength of the detected system.In the lifetime measurements, the precise results can be obtained only when thepulse duration was shorter than the lifetime value. The pulse duration of our laser is8ns, which can reach about6ns after a dye laser. In order to measure lifetimes shorterthan6ns, we designed a pulse compressed system based on stimulated Brillouinscattering theory. The pulse duration can be compressed to1.52ns when the waterwas taken as work medium, and which satisfies our needs.In this work, radiative lifetimes were measured by time resolved laser-inducedfluorescence spectroscopy in plasma produced by laser ablation. The lifetimes for28odd-parity high lying levels with energy from30635.59to42245.45cm^-1in3d34s4pand3d44p configurations of V I were measured, among which26lifetimes werereported for the first time. By measuring emission spectrum with the use of hollowcathode lamp and grating monochrometer, branching fractions for66lines of5pnp （n=7,8,11–13,17–19,27,32） and5pnf （n=4–7,9,11,13,16,18） configurations foreven-parity and5p6s for odd-parity of Sn I were obtained. Absolute transitionprobabilities and oscillator strengths for59lines were deduced from combiningbranching fractions and radiative lifetimes reported in previous paper. Therein,branching fractions for59lines and transition probabilities and oscillator strengths for52lines were reported for the first time as our best known. Using the same technique, radiative lifetime for14odd-parity levels with the energy between31654.79and47184.52cm^-1of Mo I were measured, and branching fractions for130lines in thewavelength range of275.430600.478nm belonging to13levels were measured.Combining lifetimes and branching fractions, absolute transition probabilities andoscillator strengths of these lines were also obtained. In addition,13lifetimes ofodd-parity high lying levels with energy between4802263497cm^-1of Mo II weremeasured. The lifetime values range from2.2to7.5ns, among which11lifetimes arereported for the first time. Meanwhile, cooperating with the team of Biémont fromLiege University Belgium, the theoretical lifetimes of these levels were alsocalculated using HFR method included core polarization. The theoretical results andexperimental ones are in good agreement. Theoretical transition probabilities andoscillator strengths for246lines with wavelengths from207.431to510.813nmbelonging to these levels were also calculated, and were corrected with experimentallifetimes.In summary, the radiative properties of V I, Sn I and Mo I, II were investigatedsystematically in the present work. Besides only lifetimes were measured for V I, theoscillator strengths for transitions from other three atoms were obtained by combiningthe lifetimes measured and experimental or theoretical branching fractions. Theseresults not only further supply the spectral data needed urgently in atomic physicsstudy and celestial body spectrum analysis, but also are of great value for theinvestigations in many fields such as laser physics, plasma physics and hot nuclearreaction.