Spectroscopic Study On PbF And Linear (HCCCN)_n(n=1-3) Cold Molecules Toward Precison Measurement

In this thesis,the spectroscopic studies of cold molecules related to precision measurements are conducted theoretically and experimentally.The relevant research backgrounds are described as follows.The Standard Model of particle physics predicts a non-zero value(<10^-38 e?cm)of the electronic electric dipole moment（e EDM）which indicates the existence of T-（time-reversal）,CP-（charge conjugation and parity）violation though none of the current detection schemes has confirmed it.In other words,the measurement of the e EDM would verify the Standard Model,and even further inspire new physics beyond the Standard Model.Pb F is a competitive candidate for the e EDM measurement.The energy structures and spectroscopic constants of Pb F play crucial roles in the measurement scheme.It is therefore essential to perform the spectroscopic research on Pb F molecules.In addition,the e EDM measurements involves the application of an electric field,and the actual value of the electric field strength affects the measurement result.As a result,the electric field strength should be measured,and measuring the electric field by using the pendular spectra of linear（HCCCN）_n（n=1-3）molecules is a promising application.In this thesis,the spectra of Pb F are measured and analyzed,and the theoretical study of linear（HCCCN）_n（n=1-3）pendular spectra toward measuring the electric field is carried out.The research work are briefly introduced in the following part.Firstly,in order to measure the spectra of Pb F,a new experimental system for spectral measurements is designed and setup.In this experimental system,cold Pb F molecules are generated by laser ablation and supersonic expansion,and the spectra of Pb F are measured through laser-induced fluorescence（LIF）technique.Plenty of work is done to test the cold molecule preparation system and the LIF detection system.In addition,the factors that affect the signal-to-noise ratio are optimized to achieve good fluorescence signal.The A ²Σ⁺-X ²Π_1/2（0,0）and（1,0）transition spectra of Pb F are measured with a pulsed detection laser with this spectral measurement system.And then,the B ²Σ⁺-X ²Π_1/2（0,0）transition high-resolution spectrum is measured with a continuous detection laser.Secondly,the measured spectra of Pb F are analyzed,and the e EDM-related constants are obtained.（1）The A ²Σ⁺-X ²Π_1/2（0,0）and（1,0）spectra of Pb F are analyzed,and the=0 and=1 fine structure constants of ²⁰⁸Pb F A ²Σ⁺state are derived,respectively.These constants are vital for predicting the energy level shifts of Pb F in the e EDM measurement.（2）The spectrum of Pb F B ²Σ⁺-X ²Π_1/2（0,0）is analyzed.The fine structure constants of ²⁰⁸Pb F,²⁰⁷Pb F and ²⁰⁶Pb F,together with the hyperfine structure constants of ²⁰⁷Pb F,of both the X ²Π_1/2 and the B ²Σ⁺electronic states are obtained.This is the first analysis of the high-resolution spectrum of Pb F B²Σ⁺-X ²Π_1/2 transition and the spectroscopic constants of ²⁰⁷Pb F and ²⁰⁶Pb F in the B²Σ⁺electronic state are reported for the first time.Based on the constants obtained,b _F(²⁰⁷Pb F),（207Pb）_⊥and（207Pb）_∥are given,and these parameters can be used to verify and modify the theoretical methods that calculate the internal effective electric field of Pb F in the e EDM measurement.Finally,toward measuring the applied electric field in the e EDM measurement,the pendular spectra of linear（HCCCN）_n（n=1-3）molecules are calculated,and the sensitivity and spatial resolution of measuring the electric field using（HCCCN）_n（n=1-3）pendular spectra are discussed.The pendular spectra of linear（HCCCN）_n（n=1-3）molecules under different rotational temperatures and electric field strengths are calculated by the finite element matrix diagonalization method.All the Q-branches of the calculated spectra are normalized and analyzed.It is concluded that the pendular spectra of（HCCCN）_n（n=1-3）can be used to measure the electric field.The measurement sensitivities of this proposal are calculated and compared,and the spatial resolution is also discussed.The possible applications of measuring the electric field（including the electric field in the e EDM measurement）with（HCCCN）_n（n=1-3）pendular spectra is discussed.