The Geometries And The Photodetachment Spectra Of The Halocarbene Anions HCCl~- And HCBr~- From Theoretical Investigation

In this thesis,we explore the photoelectron spectra of the HCCl~-and HCBr~-anion theoretically including singlet X~ 1A?-X~ 2A? and triplet a3A?-X~ 2A? transitions.Spectral simulation is based on iterative FC analyses and spectral simulations programs,which is our core content of the study.Geometry optimization and harmonic vibrational frequency calculations have been carried out on the X~ 2A? state of HCCl~-and HCBr~-,and the X~ 1A? and a3A? states of HCCl and HCBr by the B3 LYP,QCISD(T),and CCSD(T)levels with several different basis sets(Dunning correlation consistent cc-pVXZ and the augmented correlated consistent polarized valence aug-cc-pVXZ(X = 2,3,4 and 5)basis sets).The B3 LYP,QCISD(T),and CCSD(T)calculations were performed applying the Gaussian09 suite of programs.The Franck-Condon factors calculations on the HCCl(X~ 1A?)-HCCl~-(X~ 2A?)?HCCl(a3A?)-HCCl~-(X~ 2A?)?HCBr(X~ 1A?)-HCBr~-(X~ 2A?)and HCBr(a3A?)-HCBr~-(X~ 2A?)photo-detachment processes have been explored,utilizing the CCSD(T)force constants and structural parameters for the initial electronic state X~ 2A? of HCCl~-and HCBr~-and the final electronic states X~ 1A? and a3A? of HCCl and HCBr.It's worth noting that the Franck-Condon analysis procedure and the spectral simulation method applied in the present paper on the basis of the harmonic oscillator model and considering Duschinsky effects,which have been described in section 3.3.3.Then the calculated FCFs were utilized to simulate the vibrational structures of the singlet and triplet transitions of HCCl~-and HCBr~-.In the spectral simulation,for energy and intensity of a transition,we need to use a broadening function to broaden the peak shape of the curve.Common broadening functions including the Gaussian function,Lorentz function and Pseudo-Voigt function.In the present paper,we choose a Gaussian line shape simulated photoelectron spectra at a Boltzmann vibrational temperature of 270 K and a full-width-at-half-maximum(FWHM)of 340 cm-1.Upon an electronic transition,the normal coordinates of electronic states generally undergo a displacement distortion as well as a rotation.The rotation results in a mixing of the normal coordinates and the non-separability of the multidimensional Franck-Condon(FC)integrals.To investigate the non-radiative processes and clarify vibronic spectra of molecules,it is very important to calculate Franck-Condon factors(the square of the vibrational overlap integrals).A lot of theoretical methods have been proposed to evaluate the multidimensional FC integrals quantitatively.Recently,on the basis of the harmonic oscillator approximation including the Duschinsky effects,a more general expression has been derived by our study group.The expression is very useful for studying vibronic spectra and non-radiative processes of molecules.On the basis of GAUSSIAN09 output,the Duschinsky matrix J and displacement vector K for the transition between two different electronic states are been studied,which to determine the influence of different vibration modes of the spectrum simulation.Franck-Condon analysis and spectral simulations have been performed on the HCCl~-and HCBr~-singlet and triplet photo-detachment processes,utilizing the high level quantum chemical computations force constants and structural parameters.We studied the vibrational assignments for the X~ 1A?-X~ 2A? and a3A?-X~ 2A? detachments,respectively.It has been found that for the X~ 1A?-X~ 2A? detachment of HCCl~-and HCBr~-anion vibration assignments,the C-Cl/C-Br stretching mode ?3 is involved and the C-H stretching mode ?1 and the bending mode ?2 are almost negligible,however,for the a3A?-X~ 2A? of HCCland HCBr~-,the bending mode ?2 and C-Cl/C-Br stretching mode ?3 plays a major role,while C-H stretching mode ?1 plays a secondary effect in the spectral simulation.All in all,the X~ 1A?-X~ 2A? transition for HCCl and HCBr is mainly a single active vibrational mode(the C-Br stretching mode ?3),while for the a3A?-X~ 2A? transition appears quite congested due to two active modes(the bending mode ?2 and C-Cl/C-Br stretching mode ?3).In order to compare with the observed spectra,the two transitions were merged together.The results show that the computed photoelectron spectra are rather identical to the observed one.This means the CCSD(T)level geometry changes for the X~ 1A?,X~ 2A? and a3A? electronic states are reasonably precise,and harmonic oscillator model used ought to be relatively approximate.