Study of the A²П_i-X²∑⁺ Transition of CN Free Radical

The spectra of the （12, 6） and （7, 2） bands of the A²П_i-X²∑⁺ transition of CN free radical have been measured by Zeeman-modulation magnetic-rotation spectroscopy. The spectra have been labeled, and the molecular constants of the A²П_i state of CN have been obtained. Thethe CN moleular constants of T_v, A_v, B_v, D_v and A-doublet p_v, q_v for both v=7 and v= 12 states in A²П_i can be obtained by fitting more than 200 observed spectral lines using NewtonGaussian least square program, and the fitting errors for these bands are 0.039 and 0.046cm^-1.