Theoretical Studies Of The Morse Long Range Potential Energy Surface And Ro-vibrational Spectra For OCS-He, CH₃F-Rg And CH₃F-H₂

An explicitly potential energy surface(PES) is a prerequisite for many types of dynamics studies such as state-state reaction, quantum clusters simulation. The intramolecular vibrations and the intermolecular actions are coupled with each other. So we should consider the affection of intramolecular vibrations in calculating intermolecular potential energy surface not only for the accuracy request of the PES but also for the needs of spectrum resolution. A model is the tool for people to understand the world and explain phenomenon. A good potential model should be very helpful in fitting the ab initio results and in dynamics calculation. The study of ro-vibrational spectra is very meaningful for testing the PES and understanding the molecular dynamics information. Our mean results list below:1. Stating from the physical meaning of intermolecular force, we find the angular function that describe the anisotropy of the intermolecular PES, combine the function and the Morse Long Range(MLR) potential model, and get the new MLR model that can describe the arbitrary molecule-molecule system.2. Reported the effective four-dimensional ab initio PES, which explicitly incorporates dependence on the intramolecular Q1(O-C) stretch normal mode of OCS and is parametrically dependent on its Q3(C-S) stretch coordinate. The resulting vibrational averaged PESs provide good representations of the experimental microwave and infrared data: for 10 microwave transitions, and 51 infrared transitions of the OCS-He dimer, the rms discrepancies are only 93.2 MHz and 0.003 cm-1, respectively, which are more than four times better than previous theoretical predictions on their original potential. The calculated infrared band origin shift associated with the v1 fundamental value of 0.111 cm-1. All of these proved our PES‘s accuracy.3. Reported the four-dimensional PESs of CH3F-He,CH3F-Ne,CH3F-Ar systems that explicitly incorporates dependence on the Q3 stretching normal mode of the CH3 F molecule. We then provided the prediction of the infrared、microwave spectra and spectra transition intensity for these systems. For CH3F-He dimer, the predicted transition frequencies are in good agreement with experimental microwave data, with the root-mean-square deviation of 0.042 cm-1. These two systems are two typical model for van der walls system. The well depth of CH3F-Ar dimer is about five times of the CH3F-He dimer. The intermolecular energy of CH3F-He dimer is very small, the wave function is very diffuse. The CH3 F molecule is like a free rotor. However, the intermolecular energy of CH3F-Ar dimer is very large, the wave function is very convergent, the CH3F-Ar dimer is like a super-molecule. The interaction of molecule-Ne complex is in the middle of molecule-Rg(Rg= He, Ne, Ar). We analysis all the properties of CH3F-Ne and we find that the CH3F-Ne is much more similar with CH3F-Ar complex, comparied with CH3F-He. So we choose the rigid rotor model to label energy levels of this system and predict the rovinbrational spectra under this model. The comparison of the three systems provides an example of studying the intermolecular forces and the effect of the intermolecular energy to the ro-vibrational energy bound state and the transition line strength.4. Report the six dimension of CH3F-H2 PES that explicitly incorporates dependence on the Q3 strength normal mode of the CH3 F molecule at the CCSD(T)-F12/AVTZ level. We report the five-dimension MLR potential analytical function form for this complex. The PES wil provide a base for the next step that spectra resolution.