[Investigation of the (6, 1) and (7, 2) bands in the A 2IIi-X 2sigma+ red system of CN radical].

The CN radical was produced by Penning AC discharge of the mixture of trace acetonitrile (36 Pa) and helium (660 Pa) and the ro-vibrational spectra were measured by optical heterodyne magnetic rotation enhanced concentration modulation spectroscopy in the range of 16 850-17 480 cm(-1). 138 lines and 118 lines were assigned to the (6, 1) and (7, 2) bands in red system A 2IIi-X 2sigma+ of CN respectively, while others were due to (8, 3) band in CN red system and C2 Swan band system. More accurate molecular constants of A 2IIi (v = 6, 7) state and perturbation parameters zeta and eta between A and X states were derived based on nonlinear least-square fitting, individually, by diagonalizing the effective Hamiltonian matrix involving the perturbation elements of two electronical states and the standard deviation of fitting was less than the experimental uncertainty 0.007 cm(-1), which implied the accuracy of our results.