Optical heterodyne detected velocity modulation molecular ionic spectroscopy

Optical heterodyne detected velocity modulation molecular ionic spectroscopy is presented and employed to observe the rovibrantional spectra of O2^+ and O2^-. That the lineshape of OH-VMS is of the second derivative of Gaussian profile and its sensitivity is 3.5 X 10-s are theoretically analyzed, and they are both in good agreement with our experimental results.