Mass Resolution Threshold Ionization Spectra Of Two Benzene Derivatives

Organic matter is an important part of the earth,and it is also closely related to the life activities of human beings,animals and plants,and is one of the important basis for judging extraterrestrial life.Ion spectrum is the"fingerprint"of ions and an important basis for identifying the existence of molecules.It is of great significance in the study of combustion,electric discharge,laser-induced plasma,chemical reaction kinetics,atmospheric optics,cosmic optics and other fields.Benzene is a common organic substance.A wide variety of benzene derivatives are formed by replacing the hydrogen atoms on the benzene ring with different groups.The excitation energy,ionization energy,vibration characteristics of excited state and ion state of many derivatives have not been reported in the literature.The characteristic data of these organic molecules has important reference value for related scientific research or industrial production.Cumene and 1,3-dimethoxybenzene are important benzene derivatives,which play an important role in chemical industry and biotechnology.In this work,resonance enhanced two-photon ionization technology was used to obtain their excited state spectra.In order to obtain the cation spectra,we carried out the mass analyzed threshold ionization（MATI）spectroscopy study,and determined the accurate ionization energies and the vibration frequencies of the excited states and the ion states.Theoretical calculations were carried out using Gaussian 09software.Different methods were used to optimize the geometric structures and calculate the vibration frequencies,for the neutral ground states,electronically excited state,and the cationic ground state.The calculation results are compared with the experimental data.The experimentally discovered vibrational spectra of the excited state and ionic state were analyzed and discussed.For the cumene,the resonance enhanced two-photon ionization（REMPI）technique was used to determine the first excitation energy to be（37,668±2）cm^-1,and the vibrational spectrum of the electronic excited state S₁was obtained.Using mass analyzed threshold ionization（MATI）spectroscopy,the precise adiabatic ionization energy of cumene was determined for the first time to be（70,410±5）cm^-1,and the cation vibration spectrum was obtained.Density universal theory calculations were carried out,REMPI and MATI spectra were simulated,and the vibrational spectra of the excited state and the ground state of the cation were assigned.For 1,3-dimethoxybenzene,the precise excitation energy of1,3-diethoxybenzene and the vibrational spectrum of its electronical excited state S₁were measured by REMPI technology.The precise adiabatic ionization energy of 1,3-diethoxybenzene was determined using MATI spectroscopy.Ultraviolet-ultraviolet hole burning technology was used to determine the existence of two rotamers in the supersonic molecular beam.Combined with theoretical calculations,the configuration of the rotamers was determined,and the first electron excitation energies of rotamers I（down-up）and III（down-down）were determined to be（36,091±2）cm^-1and（36,165±2）cm^-1,the ionization energies are（62,421±2）cm^-1and（63,381±2）cm^-1,respectively.The works on 1,3-dimethoxybenzene above are reported for the first time.