Conformational Isomerization And Rydberg Excited State Dynamics Of Small Amines

As one of the most common phenomena in nature,the interaction between light and matter is the focus of scientists.Conformational dynamics is one of the many nonradiative relaxation processes on the molecular excited states formed by the absorption of light.Isomerization of conformers and other nonadiabatic dynamics play an important role in many biological processes and biotechnology,and the involvement of biological macromolecules makes the dynamics more complicated.In order to further explore the conformational dynamics of such large molecules,starting with the small molecular structures or groups that constitute large molecules is an effective method.Amine is a common group in biological macromolecules,which has very significant physiological and biological characteristics.In this thesis,liquid microjet magnetic bottle photoelectron spectroscopy and quantum-chemical theoretical calculations are used to study the conformational isomerization and ultrafast dynamics of Rydberg excited states of gas-phase triethylamine(TEA)and gas/liquid phase diethylamine(DEA).The main research work of this thesis can be summarized as the following four parts:1.Conformers distribution of TEA ground state.Using density functional theory(DFT)method,12 kinds of ground state conformational isomers are identified.Furthermore,the structures and energies of six conformation isomers with lower energy are optimized by the second order M?ller-Plesset(MP2)method.The results show that G1 and G1’ with symmetry of C3 are the most stable conformers,and two G4 and G4’conformers with unique methyl orientation are identified.The infrared spectrums of G1～G4 conformers show that the position of vibration peaks have shifted,which is mainly caused by the symmetry difference between the conformers.2.The conformational dynamics of gas-phase TEA on Rydberg excited state.The spectral splitting caused by the projection of three angular momentum components of 3p Rydberg state is observed in photoelectron spectrum,and the ultrafast internal conversion process is extracted:The 3p state reaches 3s state through an internal conversion process of 250 fs,and the energy transfer process between different conformations lasting 270 fs is observed on the potential energy surface of 3s state.Finally,the 3s state relaxes to the ground state after 64 ps.As the remaining energy of the excited molecule is deposited into the umbrella vibration mode of TEA,the ethyl chains have enough energy to rotate around the N-C bonds,thus promoting the conversion between the conformers.When higher energy pump pulse is used,the energy tends to be transferred directly to the more stable conformer during the internal conversion.3.The dissociation dynamics of gas-phase DEA on Rydberg excited state.The two main conformers of DEA ground state,TT and TG,were excited to the 3p Rydberg state and then converted to the 3s state in 54 fs.The N-H bond breaks within 90～120 fs on the 3s state.During this process,N-C or C-C bond didn’t break,nor did the transition between TT and TG conformers occur on the 3s state potential energy surface.Theoretically,this reveals the nσ*characteristic of evolution along N-H stretch coordinates on the 3 s state when DEA dissociates.The nonadiabatic relaxation of DEA on the 3 s state is characterized by N-H bond dissociation,which competes with the conformational transition between TT and TG on the 3s state.4.The ultrafast dynamics of liquid-phase DEA on Rydberg excited state.In aqueous solution,the photoelectron kinetic energy(PKE)spectrum is significantly broadened and there is also spectral splitting.Combined with the theoretical calculation,the model of the interaction between DEA and 1～10 water molecules was obtained,and the theoretical value of adiabatic ionization potential(AIP)was estimated to be 6.99 eV,which is in good agreement with 7.05 eV measured in the experiment.There is an internal conversion of 3p→3s state,and the lifetimes of 3pz and 3px,y states are 4.05 ps and 3.11 ps,respectively.It is speculated that the dissociation of N-H bond also exists in the 3s state,and the dissociation time of TT and TG conformers are 4.68 ps and 4.35 ps,respectively.These lifetimes are nearly 40 times longer than that of gas-phase DEA,because the relaxation process centered on the hydrophilic NH-is impeded by a large number of hydrogen bonds in the aqueous environment.