Theoretical Studies On The Potential Energy Surfaces And Ro-vibrational Spectra For Van Der Waals Complexes Consisting Of HF Molecule

Van der Waals(vd W)complex has attracted tremendous attention in atmospheric chemistry,interstellar chemistry,and combustion chemistry.A series of vd W complexes,containing hydrogen fluoride(HF)molecule,are of great importance on the HF chemical laser.There are many species in HF chemical laser apparatus.The collision processes between these species have significate influence on the efficiency of laser so it is the key to obtain rate coefficients in the inelastic collision reaction in order to develop the laser technique.At present,it is still difficult to measure state-to-state vibrational relaxation rate coefficients experimentally.Therefore,reliable theoretical simulations based on accurate interaction potentials between these species are highly desirable.The purpose in this work is to study the intermolecular forces of HF interacting with Ar,H2,HF itself,and H2 O,all of which are the species in HF chemical laser,by constructing their high-accuracy intermolecular potential energy surfaces(PESs)and calculating the bound states and spectra.Through the comparison to experiments,we can validate the accuracy of PESs and help to analyze the information of microwave and infrared spectra.Achievements of this work are as follows.1.Ar is the environmental gas in the laser equipment.The interaction between Ar and HF should be described precisely.Besides,Ar–HF is a prototype vd W system that an atom interacts with a nonpolar diatomic molecule.We computed the interaction energies for Ar–HF at CCSD(T)/AV5 Z level.Based on 8748 geometry points with energies,a three-dimensional(3D)PES was fitted in the way of PIP-NN.The complex was found to have a well depth of 208.08 cm-1.Based on the PES,we computed the rovibrational energy levels of Ar–HF by means of Lanczos algorithm.The errors of rotational energy levels J?10 at its vibrational ground state are smaller than 0.1 cm-1,compared with experiments,indicating a well agreement with measured data.2.H2 offers raw material in HF chemical laser,where it drew a lot of attention for H2 interacting with HF.To date,there is still no full-dimensional PES reported for this complex,but only some reduce-dimensional ones with rigid rotors approximation.The vibrational energy transfer for H2–HF can not be simulated consequently.Thus,a sixdimensional(6D)PES was constructed here.For a 6D system,it would be a tough computation task with low efficiency if grid points were used in the sampling procedure.Here,the sampling method was improved,which is to add points for many times but with a small number of points(about few thousands)at each time.In such a way,we could not only control the distribution of ab initio points but also save much computational cost.For H2–HF,there were about 35000 points selected at the level of CCSD((T)/AVQZ.The global minimum of was H2–HF located at a T-shaped configuration,and the interaction potential well depth is 368.91 cm-1.Also,the bound states were calculated.The infrared spectra in HF intramolecular stretching band were determined and compared well with experiments.In addition,infrared transition spectra of H2–DF,D2–HF,and D2–DF were predicted theoretically as well.Quantum dynamic study indicated that the result of state-to-state rate coefficients followed the normal rule of energy transfer in both the processes of pure rotational and vibrational collisional energy transfer.3.HF molecule is the primary working medium in HF chemical laser.The selfvibrational relaxation rete coefficients determine the ro-vibrational population of HF molecule.So far,the PES in literature were all constructed from very limited ab initio points and with empirical treatment.It is of urgency to investigate the shape of PES more accurately.Thus,a 6D PES for HF–HF complex was constructed at a highaccuracy CCSD(T)/AVQZ level.The intermolecular potential well depth of HF dimer is 1573 cm-1,much deeper than previous two vd W systems.To consider the HF exchange symmetry in bound state calculations,we improved the computational program by employing symmetry-adapted Lanczos algorithm.The tunneling splitting was calculated to be 0.665 cm-1,which agrees greatly well with experimental value of0.65869 cm-1,much better than 0.44 and 0.59 cm-1 on previous PESs.The new PES was found to be reliable with high accuracy.Quantum dynamic simulations based on the PES revealed a new mechanism for collisional energy transfer,that the cross section do not follow the normal rule of conservation of internal energy.The reason is found to be the strong interactions and a long life time of this complex.4.We wrote a FORTRAN program to calculate the eigenstates for systems consisting of a nonlinear molecule and a linear one,which was successfully applied to H2O–HF.Based on rigid rotor approximation,we constructed a five-dimensional PES of H2O–HF at the level of CCSD(T)-F12a/AVTZ and then calculated its bound states.The rotational transition frequencies for the ground state of H2O–HF were predicted theoretically for the first time.In future,the program can be directly used for bound state calculations of other vd W complexes containing a nonlinear monomer and a linear one.