Study On The Absorption Spectra Of The (?)A₁-(?)B₁ Electronic Transition Of H₂O～+ And D₂O～+ By Optical Heterodyne Magnetic Rotation Enhanced Velocity Modulation Spectroscopy

The water cation, extensively existing in the nature, interstellar space and interstellar materials, plays a significant role in the fields of astrophysics, environmental science, upper atmosphere and chemistry etc., which makes its investigation essential and important. At the same time, the spectroscopic analysis of H2O+ is also an indirect way to study the neutral H2O. It is well known that theA2A1 -X2B1 electronic transition of H2O+ is a typical Renner-Teller system resultingfrom the interaction of vibrational and electronic angular momenta in a linear molecule, making the Born-Oppenheimer approximation broken down. For this reason, the spectroscopic investigation of H2O+ has become a challenging field for many interested spectroscopists. The analysis of D2O+, the isotopic molecular cation of H2O+ will not only help to study the energy structure of D2O+ but also give valuable complement to the characteristics of H2O+. At the same time, the isotopic effect between H2O+ and D2O+ can be analyzed.In this paper, the technique of optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy (OH-MR-VMS) was employed to measure theabsorption spectra of three subbands of 1(0,7,0) - (0,0,0), A(0,7,0) - (0,0,0) and(0,6,0)-(0,0,0) of A2A1-X2B1 electronic transition of H2O+ including 111 spectral lines in the near infrared region from 12200-14000 cm-1. Additionally four subbands of 2(0,9,0) - (0,0,0) , A(0,9,0) - (0,0,0) , 0(0,8,0) - (0,0,0) and(0,10,0)-(0,0,0) of A2A1-X2B1 electronic transition of D2O+ including 123 spectral lines were observed and analyzed for the first time in this region. Also with this technology three subbands of (0,15,0)- (0,0,0) , (0,15,0) - (0,0,0) and(0,14,0)-(0,0,0) of A2A1-X2B1 electronic transition of D2O+ including 86 spectral lines were measured in the visible region from 16400-17600 cm-1.With the improved theoretical model, the rotational analysis of the experimentalspectra of H2O+ and D2O+ were made in detail, obtaining the precise molecular constants and rotational energy terms of the corresponding vibrational energy ofA2A1 electronic state. The high-order terms added in the Hamiltonian expressionscan somewhat reduce the fitting deviations probably caused by the strong Renner-Teller effect, anharmonicity and Fermi resonance.