A Computational And Spectroscopic Investigation Of The Two Lowest Electronic States Of The I₂⁺

Molecular ions,as transient particles,are widely used in laboratory,plasma,interstellar space and other systems.They are characterized by strong chemical activity,short lifetime and stable physical structure.At present,the study of molecular ions,especially for complex vibration and rotation structures,has attracted extensive attention,which will contribute to comprehensive understanding of the energetic structure of molecules.The cation of molecular iodine（I₂⁺）has significant importance in the field of precision measurement due to its dense spectrum in a broad spectral range.The near-degenerate vibrational level transitions of the two substates X²Π_3/2,_gand X²Π_1/2,_g corresponding to the X²Π_g state of iodine molecule ion will enhance the sensitivity of observing the time variation of the fundamental physical constantμ（m_p/m_e）.I₂⁺ion,similar to other dihalogen cations,is also a promising candidate for detecting temporal and spatial variation of physical fundamental constants.However,there are relatively few studies and reports on I₂⁺,which limits its wide applications.The work of this dissertation is consisted by two parts.In the first part,four lowestΩsubstates(X²Π_3/2,g,X²Π_1/2,g,A²Π_3/2,u and A²Π_1/2,u)of the I₂⁺cation are studied by high-precision ab initio calculations.For the other part,the enhancement factor of the variation of mass ration between the proton and electron was detected by using the transition spectra between nearly degenerate level of X²Π_1/2,g and X²Π_3/2,g states.The calculated results are compared with the previous experimental high-resolution spectra from literatures.The potential energy curves of 24Λ-S states of I₂⁺corresponding to the dissociation of I⁺（³P_g）+I（³P_u）are calculated using the multi-reference configuration interaction（MRCI）method.The calculation is based on w CVTZ-PP basis set.Then,rovibrational levels of these electronic states are derived by solving the radial Schr（?）dinger rovibrational equation.The spectral parameters of each electronic state,including the adiabatic excitation energy T_e,the equilibrium nuclear spacing R_e,the vibration constantω_e,the rotational constant Be,and so on,were fitted by the least square method based on the calculated data.Combining with the transition dipole moment matrix elements,line strengths of vibronic bands in the A²Π_3/2,u-X²Π_3/2,g system,as well as Einstein A coefficients for 45 bands withυ’=11-19 andυ"=1-5,have been derived.In order to verify the reliability of the ab initio calculation results,the calculated relative transition intensity is compared with the experimental transition line obtained by the previous high resolution absorption spectroscopy.The comparison results show a good coincidence.Later,the Einstein A coefficients are employed to compute radiative lifetimes of theυ’=11-19 vibrational levels of the A²Π_3/2,u state,the value of these levels are at the order of 2μs.The calculation results show theΩsubstate of A²Π_1/2,u of I₂⁺potential energy curve with double potential wells structure.Because of the existence of predissociation phenomenon in the electronic states of the double-well structure,its predissociation mechanism was discussed in detail.The predissociation lifetime of higher vibrational levelυ≥49 of the electronic state is calculated.It is found that the pre-dissociation life of the energy level reaches the order of picosecond atυ=58,and the dissociation rate is very high at the same time.The spin forbidden transitions between the X²Π_1/2,g and X²Π_3/2,g states provide narrow transition lines,and the near-degenerate level transitions between the two states offer enhanced sensitivity to detect the change ofμ.Finally,the rotational degenerate transition corresponding to the vibrational transition of v’=17–v"=45,v’=23–v"=52 and v’=29–v"=59 was selected,and the calculated absolute enhancement factor was approximate to5×10³ cm^-1.