Theoretical Investigations On Electronic Structures And Spectroscopic Properties Of Some Diatomic Molecules Or Cations

Molecular spectroscopy is an important approach to understand the molecular structure and properties.The molecules including P,F,O and S atoms are very important in the astronomy,atmospheric sciences and biochemistry fields,so it is valuable to study their electronic structure and spectroscopic properties in detail.For example,PO radical is an important species in the interstellar medium around the surface of the super huge star VY Canis Majoris.The Fluorine monoxide?OF?radicals are formed in the stratosphere from the reaction of F with ozone,which results in the destruction of ozone.The PF⁺ion reacted with transition metal fragments can form stable complexes,which are potential material of the energy storage system or chemically pumped laser system.The oxygen and fluorine molecular cations are one of the most abundant species in the lower ionosphere.The spectrum information of these molecules is needed widely in numerous fields.However,it's difficult to observe the low-lying excited states of these diatomic molecules or ions directly in experiment.Therefore,the accurate theoretical spectroscopic properties of the diatomic molecules including P,F,O and S atoms are meaningful.The study on diatomic potential function is one of the important branches of molecular physics.Based on Born-Oppenheimer approximately,potential energy curve?PEC?can completely describe the molecular properties,such as equilibrium geometry,energy,force constant and spectroscopic parameter.In addition,PEC is also the potential energy function of nuclear movement,which is the foundation to investigate atomic and molecular collision and reaction.So PECs are vital in the process of analyzing the formation,dissociation and the stability of clusters.Here,we mainly force on the study of the electronic structures and spectroscopic properties of PO,OF and SF radicals and PS⁺,PF⁺,O₂⁺and F₂⁺ions.Firstly,the PECs of twenty-seven?-S states of PO radical and PF⁺cation,twenty-two?-S states of PS⁺cation,twenty-one?-S states of OF and SF radical,twenty?-S states of O₂⁺and twenty-four?-S states of F₂⁺cation are constructed employing the completely active space self-consistent-field?CASSCF?method followed by the Davidson modified internally constructed multireference configuration interaction?icMRCI+Q?method in combination with Dunning's correlation consistent basis sets in MOLPRO 2010.1program package.To obtain more accurate results,the PECs are extrapolated to the complete basis set?CBS?limit by the reference energy and correlation energy separate extrapolation scheme.The potential energy are modified by the core-valence correlation and scalar relativistic corrections.Based on the extrapolated PECs with various modifications,the radical nuclear motion Schr?dinger equations are solved with the Numerov method.The ro-vibration properties are evaluated,the spectroscopic parameters,such as T_e,D_e,R_e,?_e,?_ex_e,?_ey_e,B_e and?_e are determined.The vibrational states of each electronic state are computed.Comparison with the RKR data shows that the present spectroscopic and molecular results are accurate.Secondly,the effect of spin-orbit coupling on the potential energies is studied adopting the icMRCI+Q approach in combination with Breit-Pauli operator.The PECs of 73?electronic states of PO radical,60?electronic states of PF⁺and PS⁺cation,42?electronic states of OF and SF radical,58?electronic states of O₂⁺and 54?electronic states of F₂⁺cation are computed by the ic MRCI+Q approach with the inner shell electronic correlation.The effects of spin-orbit coupling interaction on the spectroscopic parameters and ro-vibrational levels are estimated.Thirdly,the transition properties of B²?-3²?,B²?-4²?,B²?-X²?,A²?⁺-2²?⁺,C²?^--3²?^-,B²?-6²?,b⁴?-d⁴?,c⁴?⁺-b⁴?,b⁴?-3⁴?,1⁶?^--1⁶?,3⁴?-d⁴?,a⁴?^--b⁴?and a⁴?^--3⁴?^-of PF⁺cation,X¹?⁺-A¹?^-,X¹?⁺-1¹?,A¹?^--1¹?,1¹?-1¹?,a³?⁺-d³?,a³?⁺-c³?^-,a³?⁺-1⁵?⁺and b³?-d³?of PS⁺cation,a⁴?^--X²?,2⁴?^--X²?,1⁴?⁺-X²?,1⁴?⁺-a⁴?^-,E²?⁺-a⁴?^-,b⁴?-X²?,E²?⁺-X²?,B²?^--X²?,2⁴?^--a⁴?^-,C²?-X²?,3²?-X²?and E²?⁺-X²?of OF radical,a⁴?^--X²?,3²?-X²?,1²?-X²?,2²?-X²?,1²?⁺-A²?^-,3²?-A²?^-and 3²?-2²?of SF radical are studied.Their MCSCF state-state transition diople moments?TDMs?are ascertained.Using the LEVEL program,based on PECs and TDMs,the transition Franck-Condon?F-C?factors are predicted,and the strong and weak of these transitions are analyzed.These analysis help us to figure out the spectroscopic properties on the aforementioned molecules and cations,and this information will be confirmed by experiment and theory in the future and can be added to the knowledge base.On the whole,when the core-valence correlation,scalar relativistic correction,spin-orbit coupling effect and energy extrapolation are included,the spectroscopic parameters and molecular constants at the icMRCI+Q level of theory are more accurate compared with the experiments.This proves that the research methods used here are appropriate,and this study gives a way to improve the calculation accuracy on molecular spectrum.