| The spectra of molecular ions and related microscopic energy structures can serve as the basic evidences for fundamental science in the field of chemical reaction dynamics, plasma physics, combustion physics, interstellar molecule studies, bio-molecule studies, etc., and for applied science in environment monitoring, drugs detection, explosives detection, etc. Recently, the highly sensitive detection of molecular ions spectra, which are relevant to the stellar processes and life origin, is still being a hot topic. For example, H2O+ is an important species in interstellar molecule spectroscopy and bio-science researches; its absorption spectra constitute significant evidences of the existence of H2O in interstellar space indeed due to the pre-dissociation in the excited electronic states of H2O.The rovibronic spectra of H2O+ and N2+ were observed using optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy (OH-MR-VMS) in the visible region. One hundred lines of H2O+ were recorded and assigned in the region between 16600 - 17600 cm"1 with the best S/N of 65:1 and 1061 lines of N2+ in the region between 16800 - 17573 cm"1 with the best S/N of 400:1. As far as known, the absorption spectra of H2O+ were first observed in this region. Those spectra of H2O+ were analyzed and assigned to I(0,11,0)-(0,0,0) and A(0,11,0)-(0,0,0) subbands in the A2A1-X2B1 electronic transition, in which the excited state is subjected to the Renner-Teller effect making the study of those spectra rather a challenge. With the purpose of reducing the fit deviation of H2O+ spectra, this dissertation innovationally introduced a phenomenological correction in the effective Hamiltonian, by taking into account the Renner-Teller effect and the spin-orbital coupling in the upper state. The standard deviation of the fit is 0.18 cm"1, showing an improvement 50 times more better than the deviation of the infrared spectra reproduction in Huet's study [J.Chem.Phys. 107 (1997) 5645-5651]. Thespectra of N2+ were also analyzed and assigned to the (1,5) band of the system and the (12,6), (11,5) and (7,2) bands of the system, the analysis of the (7,2) band is first reported in this dissertation.Also in this dissertation, in order to assist the project of simulatingcometary spectra of H2O+ as proposed by Kawakita and Watanabe [Ap.J. 574(2002) L183-L185], and to facilitate further assignments of the experimentalspectra of H2O+, the vibronic transition moments and line intensities werecomputed for the first time using ab initio calculations results of electronicdipole moments. The multireference double-excitation configuration interaction(MRD-CI) method was utilized to carry out the ab initio calculations of theelectronic dipole moments and electronic transition moments for the A2A1 andX2B1 electronic states. Parameterized analytical functions were fitted throughthe computed ab initio data points, and furthermore the RENNER method wasutilized to calculate the line intensities and vibronic transition moments for theA2A1-X2B1 and X2B1- X2B1 electronic transition system of H2O+. The transitionwavelengths and line intensities of D2O+ were also calculated, and the resultswere used to assist the measurements and assignments of the experimentalspectra.In the experimental aspect, the optimizing of OH-MR-VMS experiment was discussed, and the minimum detectable absorption of 10-9 (1 s integrated) in magnitude has been obtained, i.e., showing an improvement of one order magnitude. The spectral profile of OH-MR-VMS was theoretically studied. As found in this study, the spectral profile of the neutral molecule is Gaussian third derivative profile, while that of the ions molecule is the mixing of Gaussian third and fourth derivative profile. Those theoretical results are consistent with the experimental observations. Meanwhile, a new empirical equation for the spectral profile of molecular ions was derived to facilitate the profile fitting of spectra and further precise determination of the center wavelength of a s...
|
PDF Full Text Request