Studies Of Radiative Parameters Of Neutral Rhenium And Rhodium

Radiative parameters of atoms and ions such as natural radiative lifetimes,transition probabilities,and oscillator strengths,etc.are important and basic data in the investigations of plasma physics,atomic physics and astrophysics.The high quality astronomical spectra with high resolution and good signal to noise ratios people obtained with the help of the development of observational techniques such as the Hubble Space Telescope Goddard High Resolution Spectrograph,provides a strong foundation for the study of the material structure,physical state and physical progress of various types of astronomical bodies.In the decades past,lots of spectra had been studied by teams at home and abroad,however among the spectra of elements being studied,the search about some elements including Rhenium and Rhodium is relatively limited.People have found that,the spectra lines of Rhenium exist in some chemically peculiar stars,and the spectra lines of Rhodium had been observed in the solar photosphere and in meteorites.Nevertheless the spectra research of these two elements is very scarce in the decades,and this directly related to the rather poor knowledge of the energy level structures of Rhenium and Rhodium and to the lack of radiative data.Consequently,the radiative lifetimes for some levels in Re I and Rh I were experimentally measured and theoretically calculated in this paper,the experimental lifetimes were combined with theoretical branching fractions to obtain semiempirical transition probabilities and oscillator strengths.The time-resolved laser-induced fluorescence technique was used to measure the natural radiative lifetimes of some levels of neutral Rhenium and Rhodium in this work.In the experiment,we employed a single-step excitation scheme.First a 532 nm Nd:YAG laser was used to ablate the Rhenium or Rhodium foil rotating in the vacuum chamber to produce plasma,then another 532 nm pulse from a second Nd:YAG laser was used to pump a a DCM dye laser to produce the fundamental frequency light.A few nonlinear optical techniques were used including a Stokes or anti-Stokes component generated by the stimulated Raman scattering in a H2 gas cell,and the second or the third harmonics from one or two?-barium borate(BBO)crystals.These nonlinear optical techniques were used to produce excited laser of needed wavelength which was next used to pump atoms from lower energy levels in the plasma to the aimed level.In the vacuum chamber the emitted fluorescence from the aimed level was separated by a monochromator and then was detected by a PMT and transmitted into an oscilloscope,and here the decay curve was recorded.Finally the decay curve was fitted in a computer to determine the natural radiative lifetime of the studied level.This paper contains two parts of detailed results as follows:1.Time-resolved laser-induced fluorescence technique was used to measure the natural radiative lifetimes of 19 energy levels of Rhenium with the energy range of32591.63?47970.82 cm^-1,among which the lifetimes of 15 levels are reported for the first time.The measured lifetime values are in good agreement with the previously published data,and they are in the range of 9.9-132 ns.And meanwhile,we theoretically calculated the lifetimes of 18 levels(32591.63?47970.82 cm^-1)and theoretical branching fractions of 47 lines belonging to the above 18 levels by a pseudo-relativistic Hartree–Fock model including core-polarization contributions method(HFR+CPOL).By combining the experimental lifetimes determined from the present work with theoretical branching fractions,a new set of semi-empirical transition probabilities and oscillator strengths for 47 Re I lines(211.089?441.089nm)from 18 levels were derived.2.The radiative lifetimes of 20 odd-parity energy levels of neutral Rhodium in the range of 31101.75?50721.44 cm^-1 were measured by the time-resolved laser-induced plasma technique.Among these 20 levels,17 out of them were measured for the first time.These results are in the range of 7.0 to 38.4 ns and their uncertainties are smaller than 10%except 11.54%for 36985.25 cm^-1 and 11.84%for40576.95 cm^-1.Theoretical lifetimes of 17 levels and branching fractions of 63 lines in Rh I were deduced by HFR+CPOL method.By combining the experimental lifetimes measured in this work with the theoretical branching fractions the semi-empirical transition probabilities g A and oscillator strengths on a logarithmic scale log(gf)for 63 lines from 17 levels were deduced.These correspond to spectral lines appearing in the wavelength range from 231 to 428 nm.In summary,we studied on and determined the radiative parameters of radiative lifetimes,brancing fractions,transition probabilities and oscillator strengths for some levels of Re I,Rh I in this paper,and many of them are high excited levels.These data enriched the atomic database and play an important role in many fields such as atomic theory research,spectroscopic analysis,nuclear fusion process simulation and laser physics,etc.