Accurate Calculations On Vibration-Rotation Spectra Of Diatomic Molecules

In this thesis,we select the O2(0,�1)and NaH diatomic molecular systems as the research targets.Two computations of explicitly correlated multireference configuration interaction(MRCI-F12)and multireference configuration interaction(MRCI)were taken into ab inito calculate the potential energy curves,spectroscopic constants,vibration-rotation spectra,dipole moment and coupling matrix elements.On this basis,we also use pump-probe technique to study high-order harmonic generation(HHG)from aligned O2 with self-made flat field grating spectrometer.The main contents are as follow:For the O2 system,MRCI-F12 and MRCI calculation in combination with three difference Gaussian basis sets of cc-pCVQZ-F 12,cc-pCVTZ-F 12 and cc-pCV6Z is adopted to study the potential energy curves on 12 electronic states of three limit lines,the core-valence electron correlation effect is taken into account our calculations.In order to consider the size consistency of MRCI-F12 and MRCI,the Davidson correction(+Q)is also included.The spectroscopic constants,including the equilibrium internuclear distance Re,the vibrational frequency coe and ?exe,the dissociation energy De,as well as vibration-rotation spectra of X2?g,a4?u,A2?u and b4?g-states Were obtained through solving the one-dimensional radial Schrodinger equation,which shows that the spectroscopic constants of the O2 system agree well with the experimental values and are more accurate than the previous theoretical values.The reliability of the MRCI-F12 method is confirmed,and the discussion indicates that the affect of the base set and the Davidson correction on the spectroscopic constants can't be neglected.Our study would shed some light on further theoretical and experimental studies on the O2+ system.For the O2(0,�1)system,a method for accurate spectroscopic constants and vibration-rotation spectrum was presented in this work and applied to ground states of O2 molecular system,which is the explicitly correlated multireference configuration interaction method(MRCI-F12)and cc-pCVQZ-F 12 basis set performed to compute the potential energy curves(PECs)of the ground states.The effects of Davidson modification,active space ?u,scalar relativistic correction and spin-orbit coupling on the spectroscopic constants were discussed.The vibration-rotation spectrum information of ground states of O2 molecular system was provided.In addition to the negative ion harmonic vibrational constants calculation need to be improved in further,the computational results show excellent agreement with existing available experimental values,and the best equilibrium internuclear distance is consistent with the experiments with five significant numbers.For negative ion system,the higher vibration-rotation levels information that have not yet been seen are given in this paper.This study provides useful information for the accurate study of ground states of O2 molecular system,especially the structure and spectrum of negative ion system.For the NaH system,MRCI calculation in combination with the dispersive full electron basis sets of cc-pwCV5Z-DK(Na)and aug-cc-pv5Z-DK(H)are adopted to study the potential energy curves on 26 states of seven limit lines of Na(3s)+H(2S),Na(3p)+H(2P0),Na(3d)+H(2D),Na(4p)+H(2P0),Na(5s)+H(2S)and Na(4d)+H(2D).In order to the size consistency of MRCI,the Davidson correction(+Q)is also taken into consideration.On this basis,we also obtained the changing rules of the permanent dipole moment,transition dipole moment and non-adiabatic coupling matrix elements with the variation of the internuclear distance.The spectroscopic constants,including the equilibrium internuclear distance Re,the vibrational frequency ?e and ?eXe and the equilibrium rotational constant Be of the 26 states were obtained through solving the one-dimensional radial Schrodinger equation,the spectroscopic constants of ground state of X1?+and excited state A1?+agree well with the previous experimental and theoretical values.Up to now,the investigations reported on the structure and spectral information of NaH molecular is limited to the ground state and the low-lying excited states,and it is a lack of spectral data for the high-lying excited states.Therefore,there is potential application to study the structure and spectral information of NaH molecular system,especially the spectral rules on the highly excited states.The characteristic of the alignment and the laser ellipticity dependence of the HHG from aligned O2 molecules is studied through the high-order harmonic spectrometer system.The changing of harmonic yield with delay time is excellent agreement with theoretical simulation.The distribution of HHG yields on laser ellipticity can be interpreted by ?g symmetry of HOMO molecular orbital.