A Study On The Spectra And Structures Of Small Molecule Ions Using Zero Kinetic Energy Spectroscopy Combined With Extreme Ultraviolet Radiation

Gaseous molecular ions are closely related to some of the most intriguing problems in modern science and play an important role in diverse research fields such as molecular reaction dynamics,atmosphere physics,plasma physics,and cosmic chemistry.At the center of the experimental studying of gaseous molecular ions is the field of high resolution spectroscopy.The zero kinetic energy?ZEKE?spectroscopy,since its original development in 1984,has become one of the default methods of choice for high resolution spectroscopy of ions.In this dissertation,by employing the ZEKE method and a tunable vacuum ultraviolet / extreme ultraviolet?VUV/XUV?radiation resource,some prototypical molecular ions are studied in detail,including the HCCCl⁺,HCCCN⁺ and AsH₃⁺ cations.The main research results are summarized as follows.?a?The spin-vibronic energy levels of the chloroacetylene cation?HCCCl⁺?up to 4000 cm^-1 above the ground state have been measured using the ZEKE method.The energy levels have also been calculated using a diabatic model,which are in good agreement with the experimental data.The Renner-Teller?R-T?parameters describing the vibronic coupling for the H-C?C bending mode,Cl-C?C bending mode,the cross-mode vibronic coupling of the two bending vibrations have also been determined using an effective Hamiltonian matrix treatment.In comparison with the spin-orbit interaction,the R-T effect in the H-C?C bending mode is strong,while the R-T effect in the Cl-C?C bending mode is weak.There is a strong cross-mode vibronic coupling of the two bending vibrations.?b?The spin-vibronic energy levels of the cyanoacetylene cation?HCCCN⁺?up to 3200 cm^-1 above the ground state have been measured using the ZEKE method.The energy levels of the degenerate vibrational modes have also been calculated using a diabatic model.Theoretical predictions are in good agreement with the experimental data.It is found that the R-T effects for the H-?CC?-CN bending and the C-C?N bending vibrations are weak,whereas it is strong for the H-C?C bending vibration.The cross-mode R-T couplings between any of the two degenerate vibrations are strong.?c?The first rotationally resolved spectrum of the arsine cation?AsH₃⁺?is recorded using the ZEKE method.The first adiabatic ionization energy of AsH₃ is determined accurately.The vibrational energy level splittings of AsH₃⁺???due to the tunneling effect in the symmetric bending?inversion?vibration?V₂⁺?are observed.A 2-D model combined with ab initio potentials is employed to calculate the symmetric bending vibrational energy levels and the results are in good agreement with the experimental data for the first few vibrational levels.The rotational constants for V₂⁺ = 0-15 have been determined,from which the corresponding bond angles and bond lengths are obtained.In addition to the symmetric bending vibration V₂⁺,the degenerate bending vibration V₄⁺ and the symmetric stretching vibration V₁⁺ are also observed.