Measurement of the autoionization lifetime of the superexcited atomic sulfur S(3s~23P~3(~2Ddeg)4d) state using tunable vacuum ultraviolet (VUV) radiation

摘要

A new method is described that combines a tunable coherent vacuum ultraviolet (VUV) radiation source and an ion velocity imaging apparatus to study the autoionization of superexcited sulfur atoms.The photolysis of CS_2 at 193 nm is used to produce metastable sulfur atoms in the ~1D_2 state.The S(~1D_2) atom is then directly excited to the neutral superexcited state 3s2~3P3(2D°)4d 0D%) at 11.317 eV with a tunable VUV photon at-121.896 nm.This excited state then undergoes autoionization into the first ionization continuum state of S~+(~4S~deg_(3/2))+e~-,which is not directly accessible from the S(~1D_2) state through optical transition.By monitoring the S~+signal in the time-of-flight mass spectrometer while scanning the excitation wavelength,the line profile of the 3s~23P~34d ~1D_2<-3s2~3P* ~1D_2 transition is recorded and found to have a full width at half maximum (FWHM) of 0.9 cm~(-1).This has been used to determine an autoionization lifetime of the neutral superexcited 3s~23P~34d ~1D_2 state of 5.9 ps.The accurate measurement of the autoionization lifetime provides a benchmark for testing fundamental theoretical models of processes occurring in excited states of atoms.