Measurement of the Absorption Spectrum of water ion in the Visible   Region
  Together with the 74 lines belonging to (0,9,0)-(0,0,0) band, the high-resolution absorption spectrum of H2O+ was observed in the visible region of 16680 -17300 (cm-1) using optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy for the first time, which verifies the high sensitivity and high signal to noise ratio (S/N) of this technique. 
Hua Zhuang, Yangqin Chen, Wenhai Ji, Shenghai Wu, Zhiyi Bi, Longsheng   Ma