| The quantum chemistry,whose theoretical foundation is the quantum mechanics and mainly tool is the computer,studies the relation of the microstructure and macroproperty of the substance and interprets the essence of the substance and chemical reaction. In this paper, we study the adiabatic potentials curves of S2+ and Photoelectron Spectra of S 2 with GAMESS program package.1.The study on the adiabatic potentials curves of S2+The atomic orbital basis set was cc-pVQZ (12s,6p,3d,2f,1g)/(5s,4p,3d,2f,1g)。A complete active space self- consistent-field(CASSCF) method was employed ,in which the 4σg, 4σu, 5σg, 5σu, 2πu and 2πg were selected to compose an active among the orbitals. Base on multi-configuration self-consistent field (MCSCF),we obtained the potential energy curves of X2Πg, a4Πu, A2Πu, b4Σg- and the adabatic potential energy curves of X3Σg- by multi- configuration quasi-degenerate(MCQDPT).The configuration of S2 molecule in ground is Thereinto 5σg22πg42πu2correspond to molecular orbital was generated by 3P electron from sulphur atom .Hence,the state of S2+ molecular ion were generated by 3P valent electron ionization as following:And the state of S2+ molecular ion were generated by 3S valent electron ionization as following:In this paper,these calculation methods that we selected were carried out in the D2 h symmetry by the procedure of GAMESS.2. Simulation of Photoelectron Spectra of S2We have fitted Spectroscopic constants using LEVEL program package by using adiabatic potentials curves and defined vibrational energy level. Franck-Condon factors between the ground state and the S2+ states were calculated in order to simulation vibration photoelectron spectra of S2 in theoretical.Intensity lines were obtained using the FCFs and the weight of the CSF which the state: 2Πg,4,2Π)u,4,2Σg.The adiabatic ionization energy of ionization spectral band from the S2 molecule of 3P valent electron are obtained ,and identify the adiabatic and vertical ionization energies of A2Πu and B2-Σg state which undetermined in experiment. Photoelectronic spectra was not included the population of S2 molecule in the X3∑g- vibration excited state that caused by temperature in the calculation , the effects would make the 0-0 shift line intensity in the direction of more peaks, v ' - v "(v '≠0) transition bands. Addition to b4∑g- peak 0-0 lines, the other location of the peaks and the largest relative intensity and spectrum in good agreement with experimental observation; the peak value of b4Σg- with 0-0 vibration transition intensity abnormalities mainly because b4∑g- state and S2 ( X3∑g-) state of equilibrium position is very close to (a difference of 0.004 nm), and two close to the shape of the potential energy curve, and this led to the almost two vibration wave function overlap so that FCF anomalies larger.
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