Transition Dipole Moments and Transition Probabilities of the CN Radical

This paper studies the transition probabilities of electric dipole transitions between 10 low-lying states of the CN radical. These states are X-2 Sigma(+), A(2)Pi, B-2 Sigma(+), a(4)Sigma(+), b(4)Pi, 1(4)Sigma(-), 2(4)Pi, 1(4)Delta, 1(6)Sigma(+), and 1(6)Pi. The potential energy curves are calculated using the CASSCF method, which is followed by the icMRCI approach with the Davidson correction. The transition dipole moments between different states are calculated. To improve the accuracy of potential energy curves, core-valence correlation and scalar relativistic corrections, as well as the extrapolation of potential energies to the complete basis set limit are included. The Franck-Condon factors and Einstein coefficients of emissions are calculated. The radiative lifetimes are determined for the vibrational levels of the A(2)Pi, B-2 Sigma(+), b(4)Pi, 1(4)Sigma(-), 2(4)Pi, 1(4)Delta, and 1(6)Pi states. According to the transition probabilities and radiative lifetimes, some guidelines for detecting these states spectroscopically are proposed. The spin-orbit coupling effect on the spectroscopic and vibrational properties is evaluated. The splitting energy in the A(2)Pi state is determined to be 50.99 cm(-1), which compares well with the experimental ones. The potential energy curves, transition dipole moments, spectroscopic parameters, and transition probabilities reported in this paper can be considered to be very reliable. The results obtained here can be used as guidelines for detecting these transitions, in particular those that have not been measured in previous experiments or have not been observed in the Sun, comets, stellar atmospheres, dark interstellar clouds, and diffuse interstellar clouds.